In order to improve the accuracy of ocean-land waveform classifications of airborne green lasers in complex ocean-land environments, an ocean-land waveform classification method based on multichannel weighted voting [i.e., multichannel weighted voting convolutional neural network (MWV-CNN)] is proposed. First, the multichannel green laser waveforms collected in the deep and shallow channels are input into the proposed one-dimensional convolutional neural network (1D CNN) module through a multichannel input module. Second, each 1D CNN module processes each channel waveform separately to obtain the predicted scores for each channel waveform belonging to the ocean and land categories. Finally, the predicted score of each channel is treated as weight, and a multichannel fusion module is used to determine the final waveform category via weighted voting. The measured data in the coastal waters of Lianyungang, China are verified by experiment using Optech CZMIL. The results indicate that the overall classification accuracy, Kappa coefficient, and overall accuracy standard deviation of MWV-CNN are 99.45%, 0.982, and 0.02%, respectively, and as compared with traditional ocean-land waveform classification methods, the proposed method exhibits better classification accuracy and robustness, thus providing a new effective way for realizing ocean-land waveform classification of airborne green laser with high accuracy.

Spatial optical couplings in atmospheric turbulence channels are associated with low efficiencies and difficult alignments, hence, in this study, a research scheme for coupling a turbulent signal beam into optical waveguides through a grating was proposed and the influence of atmospheric turbulence on spatial light and optical waveguide coupling parameters was analyzed. Moreover, a highly efficient spatial optical coupling waveguide chip was designed by optimizing the structural parameters of the grating. Additionally, three sets of Si/SiO2 mirrors were introduced to reduce the downward coupling loss and further improve the grating coupling efficiency. Simulation results show that for the spatial light affected by atmospheric turbulence, the coupling efficiency of the incident grating coupler at 1550 nm was 74% (50.5%, without adding the mirrors) when the grating period, etching depth, and lower cladding thickness were 660 nm, 100 nm, and 1.45 μm, respectively, indicating the efficient coupling of spatial light in the atmospheric turbulent channels. The findings of this study will be of great significance in improving the communication efficiency and photoelectric integration in the field of free-space optical communication.

This study aimed to assess the transmission and communication characteristics of an helical Ince-Gaussian (HIG) beams in ocean turbulence channels. First, the relationship between the transmission performance (intensity distribution, phase distribution, scintillation index, centroid drift, and overlap) and the transmission distances of an HIG beams passing through ocean turbulence was simulated based on the random phase screens and the power spectrum inversion method. Next, communication bit error rate was analyzed based on the log-normal intensity probability density function. Further, the performance of the HIG beams under different beam parameters (ellipticity, order, and degree) was analyzed and optimized to achieve optimal transmission and communication performance. The simulation results revealed that the HIG beams exhibit better anti-turbulence ability at different distances compared to the Gaussian beam. In a 100 m ocean turbulence channel (ε = 10-5 m2∕s3, XT = 10-5 K2∕s, ω = -0.15, η = 10-3 m, L0 = 10 m), the scintillation index, the centroid drift and the bit error rate were reduced by 58%, 53%, and 3 orders of magnitude, respectively. Further, the transmission and communication performance of the HIG beams decreased with the increase in turbulence intensity, and the performance improvement ability of the HIG beams also decreased compared with the Gaussian beam. The bit error rate improved by about 4 orders of magnitude under relatively weak turbulence, while it improved by about 1 order of magnitude under relatively strong turbulence. When the outer scale of ocean turbulence increased, the centroid drift of the HIG beams increased slightly, while the other parameters were almost unaffected. After optimization, ellipticity, order, and degree can improve the communication and transmission performance of HIG beams,and the order is the most sensitive parameter. The simulation results may provide a theoretical basis and a technical reference for the application of HIG beams in underwater optical communications.

To further study the application of Gaussian laser beams in underwater communication and information detection and the characteristics of the transmission process in different seawater environments, in this study, the most-common terrestrial suspended sediment particles in seawater were taken as an example. First, Mie scattering theory was combined with the Monte Carlo method to establish a 520-nm Gaussian laser transmission model in seawater containing suspended solids, and the effects of particle groups with specific diameters and densities on laser transmission were studied. Second, the variation in the normalized received power with the initial divergence angle of the laser at different detection distances was analyzed. The research results indicate the following. 1) When the diameter and density of suspended sediment particles in the Mie scattering model are changed, thereby changing the extinction coefficient, scattering coefficient, and asymmetry factor set in the simulation, the received power of the detection target decreases exponentially with increases in scatterer diameter, density, and transmission distance. 2) Within a certain range, the change in the initial divergence angle does not affect the power of the receiving surface, and this range decreases with increases in the scattering coefficient and transmission distance. The research method used lays a theoretical foundation for further analyzing the changes in Gaussian laser transmission characteristics in seawater containing complex particle groups (suspended bubbles, planktonic algae, and suspended sediment) and provides reference for related engineering estimates.

Space-borne Mie lidar is the most widely used instrument to profile aerosols in the global scale. However, due to the variation of atmospheric aerosol types, the retrieval model for aerosol extinction coefficients from lidar signals assumes a prior aerosol model, which impedes the further improvement of retrieval accuracy. As such, an iteration algorithm for aerosol extinction coefficient profiling from space-board dual-wavelength lidar observation is proposed. First, the initial extinction-to-backscatter ratio (i.e., lidar ratio) is obtained based on a prior aerosol mode and the aerosol extinction coefficient and optical depth at two channels are then retrieved. Moreover, with the relationship built between aerosol optical depth and aerosol mass column, the total aerosol mass columns at two channels are estimated. Finally, by applying the constraints that the two-channel observations correspond to the same aerosol mass column, the lidar ratio and the optical parameters are optimized iteratively based on lidar observation extensively. Due to the limitation of the channel number of the dual-wavelength lidar, the method is only applicable to the two-type mixed aerosol model. The accuracy and the applicability of the method are evaluated based on the background information of aerosol profiles in Baotou, Inner Mongolia, China. The retrieval results from the empirically estimated lidar ratio are taken as the control group. The results show that the proposed method yields mean accuracy improvement of extinction coefficient at 532 nm and 1064 nm channels by 21.16% and 3.00%, respectively. The method is also applied to CALIOP data to further validate the application potential of the proposed retrieval model.

The high-precision reconstruction of an underwater neighborhood sound field is crucial for studying and analyzing the structural characteristics of neighborhood sound field and improving the underwater acoustic sensing performance. The deflection effect of the laser beam passing through the acoustic field carries the gradient and pressure information of the acoustic field when the laser beam width is much smaller than the acoustic wave wavelength. This study provides a data sensing basis for sound field reconstruction by employing the Kirchhoff integral theorem. The calculation method of a virtual extended acoustic field aperture is presented herein by using the density of the laser sensing acoustic field, which further approaches the theoretical requirement of the infinite integral interval in the Kirchhoff integral theorem. The results of the proposed sound field reconstruction ideas and methods are verified in an underwater neighborhood space. The results show that, compared with direct acoustic holography, the proposed acoustic field reconstruction method improves the peak signal-to-noise ratio by 5.5 dB, thereby providing a new feasible idea for developing high-precision neighborhood acoustic field sensors.

Existing theoretical models of skylight polarization patterns have problems that only consider the influence of the sun or the moon alone and could not adequately describe the polarization patterns of the sky during the transition between dawn and dusk in clear weather. Therefore, a modelling method of skylight polarization patterns under the influence of dawn and twilight is proposed. The method introduces the influence of the sun and the moon and calculates the Stokes vectors using the position of the sun and the moon. Considering the factors of multiple scattering of atmospheric particles in the actual sky, the influence weights of the sun and the moon are determined by Stokes vector optimization. In addition, the obtained angle of polarization is used to characterize the skylight polarization patterns. The experimental results show that the simulation results of the proposed model and the measured angle of polarization have the same distribution and variation characteristics, and maintain a high degree of similarity, which can effectively characterize the skylight polarization patterns influenced by dawn and twilight.

The content of Bromine was measured by X-ray fluorescence approach in order to study the spatial distribution characteristics of Bromine in seawater and analyze the reasons that affect the distribution of Bromine near the Eastern shore of Leizhou Peninsula. First, the calibration curve of standard solution is obtained by small-focus X-ray fluorescence spectrometer and direct injection method, and the linear fitting equation is derived from the relationship between the fluorescence intensity and the mass concentration of Bromine, to detect the mass concentration of Bromine in coastal waters. Then, we further analyze the influences of the land runoff, tide and the structure of circulation on the distribution of Bromine in seawater in the east of Leizhou Peninsula based on the spatial variation of Bromine mass concentration in water, the spatial distribution of land runoff, tide and the structure of circulation. The Bromine mass concentration of 18 stations in the east of Leizhou Peninsula is in the range of 50.79?62.11 mg/L derived by the X-ray fluorescence spectrometry approach, and the results indicate that the content of Bromine in this area is less than that in the ocean and varies greatly with space. In this area, the Bromine content almost increases with the distance between the sampling site and two-bays-one-island (Zhanjiang bay, Leizhou bay and Naozhou island) increasing. In addition, in the south of this area and the entrance of Qiongzhou Strait, for the complex influences of currents, the Bromine content increases along the flow direction of Qiongzhou Strait. The variation of Bromine mass concentration in coastal waters demonstrates that the distribution of Bromine is uneven, and the uneven distribution fact of Bromine is mainly caused by the land runoff, tide, alongshore current near Western Guangdong, Qiongzhou Strait current, and cyclonic circulation.

Problems such as image color distortion, blurred image details, and image artifacts are prone to occur in the current dehazing algorithm. In order to solve the above problems, an image dehazing algorithm with parallel multi scale attention mapping is proposed. The algorithm achieves image defogging through an end-to-end encoder decoder structure. In the encoder stage, the continuous downsampling layer is used to reduce feature dimension and avoid over-fitting. In the feature transformation stage, a parallel multi scale attention mapping block with a parallel branch structure is designed, so that the model can make full use of multi scale features while focusing on important features of the image, and effective collection of image spatial structure information by connecting selective feature fusion block in parallel. In the decoding stage, the upsampling layer is used to reconstruct the image, and through skip connections of up and down sampling to better preserve image edge information. Experimental results show that the algorithm has better dehazing effects on both synthetic hazy datasets and real hazy images. Compared with traditional dehazing methods, this algorithm better preserves image details and has better color retention.

Real-time detection of aerosol flow field using planar laser-induced fluorescence (PLIF) technology is crucial for studying the motion of aerosol. To enhance the visibility of weak signals in real-time PLIF aerosol signal detection, we propose a method of piecewise intensity transformation in this paper. This method sets constraints based on the characteristics of signal intensity, iteratively divides the signal into several intensity ranges, and then replans the signal intensity in each range. The proposed piecewise intensity transformation is applied to the signal processing of PLIF aerosol flow field detection,compared with the processing results of limited contrast adaptive histogram equalization (CLAHE), this method has good results in weak signal enhancement and noise suppression of large dynamic range fluorescent signals, with an improvement of over 20% in the signal-to-background ratio of weak signals. The proposed method achieves real-time detection at 25 frames per second for different stages of aerosol flow field, meeting the requirements for real-time detection of aerosol flow field fluorescence signal.

Aiming at the problem that the semi-empirical model in the aerosol fine particle retrieval algorithm on the directional polarimetric camera(DPC) platform carried by the GF-5 satellite is not suitable for the estimation of urban surface polarization reflectance. In this paper, based on the empirical orthogonal function method of DPC, the inversion of the optical thickness of aerosol fine particles is carried out. The aerosol radiative contribution is calculated based on Mie scattering, the surface contribution is calculated by the empirical orthogonal function method, and the optical thickness of aerosol fine particles is inverted by using the multi-angle polarization data and the vector radiative transfer equation. The inversion results of this study are consistent with the moderate-resolution imaging spectroradiometer distribution trend of aerosol fine particle optical depth products, quantitatively compared with the measurement results of AERONET Beijing, Xianghe, and Hong Kong stations, the correlation coefficients are 0.97, 0.96, and 0.9, the mean absolute error is 0.08, 0.07, and 0.12, and the root mean square error is 0.12, 0.11, and 0.17, which verifies the high precision and rationality of the algorithm. Finally, the monthly average data of aerosol fine particle optical thickness in some areas of China in 2019 are presented, and the changes of aerosol fine particle optical thickness in Shandong are analyzed. It is found that June is the highest period of the year, with an average value of 0.7. The above results verify the reliability of the algorithm and provide technical support for DPC to effectively monitor the spatiotemporal distribution of aerosols

The diffuse attenuation coefficient of downwelling irradiance (kd) is one of the most critical optical parameters in oceanic optics. The optical parameters of waters around the Dalian port polluted by dispersed oil (oil in water) were measured, and the underwater light field was simulated using the radiative transfer model (Hydrolight) to analyze the influence of oil in water on kd and to establish a semi-analytical model for kd. The simulation results show that the kd spectra of various water depths increase with increasing oil concentrations. Moreover, kd increases with increasing depth, particularly for the waters containing high concentrations of dispersed oil, and the faster it approaches its steady asymptotic value. In addition, this study also shows that the contributions of the absorption coefficient (a) and backscattering coefficient (bb) to kd of water polluted by dispersed oil differ from those of a and bb to kd of natural water body, so that the parameter values of the kd semi-analytical models of water polluted by dispersed oil and natural water body are significantly different. Therefore, the existing kd semi-analytical model for natural water body is unsuitable for accurate calculations of kd of water polluted by dispersed oil. Hence, a semi-analytical model of kd was developed based on the simulation results of Hydrolight. The accurate downwelling irradiance can be further calculated using kd obtained with this developed semi-analytical model to provide a rapid and reliable solution for the underwater light field simulation of waters polluted by dispersed oil.

This paper presents a method for high-dimensional information modulation and demodulation using a vortex beam for underwater wireless optical communication by identifying the superposition state of orbital angular momentum in the vortex beam. The method and process of identifying the superposition states of two vortex beams are described. The topological charge numbers in the superposition states are obtained based on the light intensity distribution diagram of the superposition states after water channel transmission. Based on the results, it is experimentally demonstrated that the superposition state of orbital angular momentum can achieve the modulation and demodulation of 16-dimensional information under low-topological-charge conditions. Thus, this study provides a feasible scheme for applying vortex beams in underwater wireless optical communication.

With the completion and use of BDS-3, this paper proposes two improved methods for retrieving tide surface height from global navigation satellite system reflectometry (GNSS-R) based on the BDS-3/GPS multi-frequency signal to noise ratio data, namely, method of eliminating gross errors based on the relationship between the highest peak and the second peak and the method of optimal frequency band. The effectiveness of the method is verified by the observation data of 333-337 consecutive 5 days of accumulated days (DOY) in 2020 at the MAYG station on Mayotte near the Indian Ocean. The results show that the method of removing gross errors based on the relationship between the highest peak and the second peak can improve the accuracy of tide level inversion. The GPS frequency band is increased by 9.16% and the BDS frequency band is increased by 17.34%, but it will reduce the number of inversion results. The optimal frequency band correction method can improve the accuracy while increasing the number of inversion results. The inversion accuracy of the corrected GPS S1C and S2W frequency bands is increased by 26.54% and 22.89%, respectively. In BDS S1X, S2I, S6I, and S7I, the 5-day tide level inversion root-mean-square error decreased by 61.36%, 34.23%, 47.68%, and 55.38% respectively. The accuracy improvement is higher than the former.

A continuous zoom optical system for underwater that has the characteristics of a large field of view, high resolution, and high zoom ratio at the same time is designed to satisfy the needs of deep-sea exploration and achieve higher quality optical imaging in the deep sea. According to the operating deep sea environment, the image quality degradation caused by the extrusion deformation of the optical window caused by deep water pressure was considered, an integrated optomechanical analysis of the optical window was carried out, and the surface shape change results were substituted into the optical system in the form of a Zernike polynomial for optimization. After studying the characteristics of underwater optical aberration and the design method of zoom system, the optical system adopts the mechanical negative group compensation zoom method and image square telecentric design scheme. The system's working distance is 5 m, the F-number of the whole zoom is constant 3.0, and the system can achieve the full field of view of 5.7°-90°, 10 times continuous zoom. The zoom system uses three aspheric surfaces with a total length of 260 mm. At 208 lp/mm, the maximum distortion of each zoom position of the system is <3% and the modulation transfer function values of the entire field of view in the whole zoom area are >0.3. The zoom system features a compact structure, good imaging quality, and a smooth zoom curve, which can accommodate real application demands.

Sea surface temperature (SST) is an important marine hydrologic parameter, and its accurate prediction is critical in marine-related fields. Deep learning has been widely and increasingly used for SST prediction in recent years because of its strong analytical ability. However, the volatility and randomness of SST time series still constitute a challenge for accurate prediction. In this study, variational mode decomposition (VMD) is first introduced as a denoising module to reduce the influence of SST sequence noise on the prediction results. Then, to solve the lag phenomenon of depth models in SST prediction, the method of transfer learning is adopted to combine the concepts of long-short term memory (LSTM) and broad learning system (BLS). LSTM is used as the feature mapping node of BLS to improve the prediction accuracy. As a result, an SST prediction model based on VMD, LSTM, and BLS is proposed. The SST of the East China Sea is selected as an example for verification. By comparing with benchmark models, support vector regression (SVR), LSTM, gate recurrent unit (GRU), and existing deep models, it is shown that the proposed model is relatively stable and efficient in SST prediction, which provides a new idea for the development of SST prediction.

To address the issue of picture blur and color distortion in underwater images of complex water bodies, an underwater image restoration algorithm based on HSV classification, CIELAB equalization, and minimum convolution region dark channel prior (DCP) is proposed. By the thresholds of H and S, the underwater photos are separated into high saturation distortion, low saturation distortion, and shallow water images. Then, the underwater image is recovered using CIELAB equilibrium and adaptive image enhancement, where the system parameters of the categorized underwater image are estimated by minimum convolutional area DCP. The experimental findings demonstrate that the suggested solution is superior to the comparison algorithms in image restoration effect, evaluation quality, and real-time performance indicators. The average peak signal-to-noise ratio and structural similarity values are increased by 26.88% and 17.3% on average, respectively, and the underwater image quality measurement value is increased by 4.3%.

Building extraction from remote sensing images is of great significance to the construction of smart cities. Aiming to improve the low accuracy of traditional methods in extracting remote sensing images with a complex background, a remote sensing image building extraction method (MA-Unet) based on U-Net is proposed. This method mainly uses an encoder and a decoder. A convolutional block attention module is introduced into the encoder, in which a channel attention module is used to screen more important features and suppress invalid features, and a spatial attention module is used to screen deeper semantic features. An atrous spatial pyramid pooling module is introduced to extract features with different scales. In the decoder, to fuse object features with different scales, feature maps in the decoder are upsampled and connected in series. This information aggregation solves the difficulty of detecting objects with different scales to some extent. The experimental results show that MA-Unet method is superior to the U-Net method in terms of accuracy, precision, and intersection over union (IoU) by 1.7 percentage points, 2.1 percentage points, and 1.6 percentage points on the Massachusetts building dataset and by 1.1 percentage points, 1.4 percentage points, and 2.3 percentage points on the WHU building dataset, respectively. It is a more effective and practical target extraction method.

The resolution of a ground-based large-scale aperture telescope can be severely deteriorated by atmospheric turbulence. Adaptive optics (AO) systems have been widely used thus far to solve this problem. However, correction using AO is a partial solution. Degraded images generated by residual wavefronts can be restored via post-reconstruction. In this paper, a blind deconvolution algorithm to improve the quality of Poisson noise astronomical images acquired after AO correction is proposed. The algorithm uses an adaptive L1 norm term in the gradient domain for an accurate estimation of the point spread function (PSF) as well as the Richardson-Lucy algorithm followed by a low pass denoising filter to solve Poisson deconvolution. Experimental results for simulated and real astronomical images demonstrate that the proposed algorithm can obtain better PSF and reconstruction images than other algorithms and significantly improves the quality of post-AO astronomical images without further information.

Changes in various weather phenomena are accompanied by the movement of clouds. Continuous satellite cloud images obtained by meteorological satellites contain considerable spatio-temporal sequence information; that is, continuous satellite cloud images have significant time sequence characteristics, which can be used as basic information for cloud image prediction. Cloud image prediction is essentially a video prediction problem in which the spatio-temporal sequence characteristics of cloud images are analyzed and processed. To accurately predict the change in the position of clouds, by focusing on the unstable and nonlinear motion characteristics of clouds, a video prediction algorithm called SmartCrevNet for cloud image prediction based on the CrevNet video prediction model is proposed. In this algorithm, a spatiotemporal attention gated recurrent unit (STA-GRU), along with the lightweight attention module spatial group-wise enhance (SGE), is introduced into the original two-way autoencoder module of CrevNet to enhance the ability of feature extraction without increasing the amount of calculation. The algorithm was tested on the public dataset MovingMNIST and the FY-4A satellite cloud image dataset. The results show that, on the FY-4A satellite cloud image dataset and MovingMNIST dataset, the mean square error (MSE) of SmartCrevNet is, respectively, 7.3% and 6.1% lower than that of CrevNet, and the structural similarity (SSIM) is increased by 7.9% and 1.2%, respectively. The prediction effect is better than that of CrevNet and traditional video prediction algorithms.

The refractive index structure constant Cn2 is an important atmospheric parameter reflecting turbulence intensity. Herein, a new Cn2 inversion method is proposed based on the coherence length r0 and isoplanatic angle θ0 data of the entire atmospheric layer to address the problem related to the fact that many initial input data are needed for inversion and inversion without single type data. Based on the generalized Hufnagel-Valley (HV) turbulence model, the theoretical relationship between r0 and θ0 is deduced. Based on the measured data of r0 and θ0 in Nanshan, Xinjiang, the seven parameters of the generalized HV model are obtained using inverse calculations followed by the determination of the Cn2 profile. These seven parameter values are substituted into the deduced theoretical relationship of r0 and θ0 to calculate the value of θ0 on any single day. The simulation results show that the variation trend of the fitted average Cn2 and single-day Cn2 profiles are in good agreement with the Xianghe model, and the coincidence degree is high. The average value of the daily correlation coefficient between the calculated and the measured θ0 profiles reaches 81.95%, and the highest value is 87%. The results verify the feasibility of the proposed method and provide a reference for the inversion of the Cn2 profile.

In order to study the optical properties of different modes of marine atmospheric aerosols, coarse and fine modal classification and complex refractive index inversions are carried out and studied based on the Mie scattering theory of spherical particles. This is done using tools such as a visibility meter, automatic weather station, optical particle counter (OPC), and cavity attenuated phase shift (CAPS) single scattering albedo monitor. The inversions are carried out for atmospheric aerosols in the coastal waters of Maoming, Guangdong. The results show that the refractive index of fine-modal aerosol at 530 nm is approximately 1.35 (±0.01)?0.019 (±0.003)i when the relative humidity is greater than 55%, and it is 1.37 (±0.02)?0.020 (±0.003)i when the relative humidity is less than 55%. The refractive index of coarse-modal aerosol is approximately 1.40?0.002 (±0.002)i when the relative humidity is greater than 55%, and it is 1.48 (±0.02)?0.005(±0.002)i when the relative humidity is less than 55%. There is a clear difference in the refractive indexes of aerosol particles in different modals, which has a reference value for studies of the marine aerosol climate effect and the establishment of aerosol models in the Maoming sea area.

In this study, the polarization properties of light scattered by aerosols are investigated in actual atmospheric conditions at different visibilities considering the multiple scattering effects and the Earth's surface reflection. The vector radiation transfer equation is solved using the successive order scattering method. First, the visibilities of all the days in 2019 are evaluated. Representative high- and low-visibility atmospheres are then used as the transmission media. The macroscopic information and the microphysical properties of the aerosols provided by AERONET are used in the numerical simulations of the polarization properties of the scattered light. The coupled-surface reflection model is subsequently used to determine the properties of light scattered by the Earth's surface. The Stokes vectors are obtained as the simulation results, and the polarization degrees of the scattered light are derived. Our simulation results show that the aerosol scattering properties tend to be different in high-visibility weather conditions compared to low-visibility ones. As the solar zenith angle increases in low-visibility weather, the I, Q, and U elements of the first-order downward scattered light vary irregularly. However, these elements increase at all the orders of upward scattered light and at the high-order downward scattered light. Conversely, for high-visibility weather, the values of the I, Q, and U elements of all the scattered light orders that possess similar variation characteristics, increase with the solar zenith angle. The corresponding polarization degrees exhibit similar trends. The results of our study can be useful for the remote sensing of the polarization properties of aerosol scattered light and for determining the microphysical properties of aerosols.

The sun glint observation mode is adopted when a satellite payload detects greenhouse gases over the ocean to obtain high-precision gas concentration data. Therefore, accurately calculating the real-time sun glint position is a prerequisite for obtaining high-precision data. An improved sun glint calculation model based on an optimal line search is proposed. According to the WGS-84 ellipsoid model, on the basis of dichotomy searching to meet the requirements of specular reflective speckles, the algorithm is improved by using the idea of optimal line search to better meet the coplanar condition of the sun glint. Compared with the simulation results of the Satellite Tool Kit (STK), the sun glint position distance error calculated by the improved model is significantly reduced to 90 m.

In the supersonic flight state of 3 Ma (1 Ma≈340.3 m/s), the temperature of the optical window heated by aerodynamics rises sharply, resulting in a large amount of infrared thermal radiation, which interferes with the imaging quality of the detector. In order to study the influence of aerodynamic thermal radiation on infrared imaging, this paper used ANSYS software to perform 3D modeling, finite element meshing and temperature field simulation on the seeker model; by using Planck's blackbody radiation formula and TracePro software, the irradiance generated by the target source and the optical window at different temperatures were calculated and simulated, and the signal-to-noise ratio model was established to analyze the influence of the temperature of the optical window and the relative distance of the target on the infrared imaging quality of the seeker. The results showed that the signal-to-noise ratio of the infrared imaging system decreased by 91.8%, 50.1%, and 20.7%, respectively after the seeker flew at an altitude of 2 km, 11 km, and 20 km for 10 seconds. The decrease of signal-to-noise ratio will seriously affect the imaging quality of the infrared system, and the cooling measures must be used to cool the optical window for reducing the interference. This paper will provide data reference for the design of the optical window of the seeker and the optical detection system, and will provide theoretical basis for the research on overcoming the interference of aerodynamic heat radiation.

Generative adversarial network (GAN), a deep learning technique, is widely applied in the field of remote sensing because of its ability to extract features from large input data and generate more realistic forecasts of meteorological images. At present, however, the application of GANs in atmospheric motion vector (AMV) retrieval is rare, although AMVs are important data source for numerical weather prediction (NWP), especially in data assimilation. Based on this, a method for retrieving AMVs from geostationary satellite images using pix2pix, a type of GAN, is proposed. The pix2pix model is used to convert remote sensing images into wind vector fields at 850 hPa and 200 hPa. With the best data and model architecture, the AMVs obtained by this method are comparable to the AMVs retrieved using traditional algorithms. This method avoids the drawbacks of traditional algorithms, such as the inability to obtain complete wind fields at a certain level, difficulty of height assignment, and sparse AMVs at lower atmospheric levels. Case analysis shows that this method also performs well for specific weather systems.

Vortex optical multiplexing communication technology can effectively improve the channel capacity of a communication system in an underwater channel. However, ocean turbulence causes the inter modal crosstalk of the vortex beam, degrading the performance of the communication system. To alleviate the modal crosstalk problem, this study presents a blind equalization algorithm based on a back propagation (BP) neural network. Four channels of vortex light are used for multiplexing transmission, and the random phase screen method is used to simulate ocean turbulence. After the BP blind equalization algorithm is implemented, the improvement in the system bit error rate is simulated and analyzed under conditions of varying ocean turbulence intensities, transmission distances, and vortex light multiplexing modes. The simulation results show that the blind equalization algorithm using the BP neural network can effectively reduce the impact of ocean turbulence on the bit error rate of the system, and the system performance significantly improves when the multiplexing mode interval is 2.

The aerosol optical depth (AOD), Angstrom exponent (AE), single scattering albedo (SSA), and fine mode fraction (FMF) were extracted through six AERONET long-term observation sites, including Beijing-RADI, Beijing-CAMS, Xuzhou-CUMT, Taihu, Hong_Kong_PolyU, and Hong_Kong_Sheung locating along the coastline of eastern China, and were processed using the Terra/Aqua MODIS level2 C6 AOD products to study the aerosol variation characteristics and type characteristics of aerosols in eastern China. It is found that 1) the annual average value of AOD decreases from Xuzhou to Taihu, Beijing, and Hong Kong in the order 0.805±0.129、0.775±0.069、0.664±0.197, and 0.519±0.125, respectively; 2) at the AERONET site location, the annual average value of MODIS AOD decreases from Taihu to Xuzhou, Hong Kong, and Beijing in the order 0.902±0.227, 0.772±0.082, 0.547±0.064, and 0.517±0.234 and the ground detection differences are 22.2%, 4.1%, 5.5%, and 16.3%, respectively; 3) the annual average AE value decreases from Hong Kong to Taihu, Xuzhou, and Beijing in the order 1.314±0.054、1.213±0.084、1.198±0.104、and 1.118±0.078, respectively, indicating that the average size of air pollutant particulates in eastern China decreases from north to south; 4) the proportions of weakly absorbable fine particles are 38.29%, 44.99%, 44.30%, and 48.14% in the four regions of Beijing, Xuzhou, Taihu, and Hong Kong, respectively, followed by moderate absorption fine particles and strong scattering fine particles. Other types of particles are found in lower concentrations.

Air pollution greatly impacts the productivity and life of people. Aerosol is an important pollutant and cannot be ignored. It is significant to improve the detection accuracy of atmospheric aerosol concentrations, especially low-concentration aerosols. In this study, filament-induced fluorescence spectrum (FIFS) of NaCl aerosol is preprocessed and combined with partial least squares (PLSR) to establish a prediction model and explore the impact of different preprocessing methods on the detection accuracy of the model. To choose the preprocessing method, this study divides the preprocessing methods into three aspects according to their effects: scattering correction, smoothing and denoising, and baseline correction, and the significance of peak algorithm is proposed. The optimal preprocessing method is selected after comparing no preprocessing, single preprocessing, and combined preprocessing and analyzing the influence of different preprocessing methods on the accuracy of FIFS spectral prediction model. The experimental results show that the combined preprocessing of multiple methods reduces the root mean square error to 0.03 compared with no preprocessing, and the relative prediction error is reduced by 60%. Compared with the direct observation of spectral signal selection preprocessing method, the best preprocessing method can be selected more accurately according to the improvement of spectral signal-to-noise ratio and the modeling effect of predicted components. The present study provides a reference for the analysis and research of low-concentration air pollutants.

Herein, the prediction accuracy of three tropospheric refractive index profile models commonly used at home and abroad was analyzed using the measured data of the tropospheric zenith delay and meteorological environment obtained from 11 international global positioning system service stations in China. Moreover, the applicability of the models was evaluated in high altitude areas and with seasonal changes. Results show that the exponential and segmented models achieve a higher accuracy at high altitude areas, while the Hopfield model shows greater advantages in areas other than high altitudes. Generally, the accuracy of the segmented and Hopfield models is higher in spring and winter and lower in summer and autumn. The accuracy of the exponential model shows a negligible relation with the season. The findings of this study have important reference values for the application research of the tropospheric refraction error correction model.

This work improves and applies the adaptive particle swarm optimization algorithm to the study of statistical model fitting of atmospheric turbulence profiles. First, an improved adaptive particle swarm optimization algorithm is proposed to improve the speed of particle swarm optimization and avoid falling into the local optimum. The distance between the current particle and the global optimal position is used to adjust the inertia weight coefficient and make nonlinear adaptive changes. The self-learning and social learning factors are based on the concept of symmetrical linear change to realize the adaptive change of the optimization focus in each stage. Second, the improved adaptive particle swarm optimization algorithm is introduced to solve the generalized Hufnagel-Valley turbulence model in Ali region, and the turbulence model profiles of morning, evening, and four seasons in the region are fitted. The simulation results show that all the decision coefficients are greater than 0.997, which agrees well with those of the statistical average profiles obtained by radiosonde. The proposed method has similar convergence accuracy to other adaptive particle swarm optimization algorithms, but the speed is faster. This paper introduces a new method for fitting Hufnagel-Valley turbulence profile models.

The modified Gamma distribution and Mie scattering theory were used to examine the light scattering attributes of water cloud particles to investigate the effect of water cloud on quantum interferometric radar (QIR) performance parameters, and a relationship was developed between water content and extinction coefficient of four common water cloud particles. For the polarization state of light quantum, the polarization change law of QIR detected photon under the background of water cloud particles is researched, and the mathematical model of the effect of water cloud particles on the transmission distance, resolution, bit error rate, and the survival performance of QIR detected photon is established. The theoretical analysis and experimental simulation results show that the extinction coefficient linearly increases with the increase of water content in the water cloud, causing the increase of attenuation coefficient, thus increasing the energy dissipation of the detected photon and decreasing the transmission distance of the detected photon. When the number of emitted photons remains constant, the resolution of QIR decreases with the increase in the optical thickness of water cloud particles. When the concentration of water cloud particles remains constant, the bit error rate of the system decreases with the increase of the depolarization ratio. When the number of detectable points of the target is constant, the greater the interference intensity of the water cloud to the QIR system is, the lower the survival performance of the radar is. To improve the detection performance of the system, each index parameter of the QIR system should be adjusted adaptively according to the relevant parameters of the water cloud in the design, debugging, and use of QIR.

For the current inspection mode of high-voltage transmission lines in power grid of China, it is mainly through manual hand-held instruments or naked eyes to inspect facility defects,which is not only difficult and intense, but also inefficient, and cannot adapt to the safe operation and development of modern power grid. In recent years, with the rapid development of unmanned aerial vehicle technology and related sensor technology, unmanned aerial vehicle has been widely used in electric inspection. Therefore, a real-time localization and map construction (SLAM) scheme based on lidar and unmanned aerial vehicle near high voltage tower is proposed. In this scheme, lidar is used as the sensor to sense the environment, different matching algorithms are used to match the secondary point cloud, and loopback detection technology is used to achieve the precise positioning of unmanned aerial vehicle and the map construction around the tower. Experimental results show that this scheme can greatly improve the positioning accuracy of unmanned aerial vehicle around the pylons, thus improving the efficiency and flight safety of unmanned aerial vehicle.

Terahertz (0.1-10 THz) band communication is envisioned as a key technology of future wireless communication because of its technical characteristics, such as super large bandwidth resources and super high communication rates. Herein, ray-tracing techniques and Beckman-Kirchhoff scattering theory are used to modify a unified multi-ray channel model in the terahertz band. The model combines direct, reflection, and scattering, and is supported by experimental data from the literatures. Furthermore, the wideband channel capacity usage is characterized using equal power and water-filling power allocation strategies. The simulation results show that the importance of resource allocation in exploiting the terahertz spectrum due to its extremely high frequency-selectivity. The study will provide some guidance for future research and design of the terahertz communication systems.

This study proposes a generative adversarial network (GAN) based on bidirectional multi-scale feature fusion to reconstruct target celestial images captured by various ground-based telescopes, which are influenced by atmospheric turbulence. This approach first constructs a dataset for network training by convolving a long-exposure atmospheric turbulence degradation model with clear images and then validates the network's performance on a simulated turbulence image dataset. Furthermore, images of the International Space Station collected by the Munin ground-based telescope (Cassegrain-type telescope) that were influenced by atmospheric turbulence are included in this study. These images were sent to the proposed neural network model for testing. Different image restoration assessment shows that the proposed network has a good real-time performance and can produce restoration results within 0.5 s, which is more than 10 times faster than standard nonneural network restoration approaches; the peak signal to noise ratio (PSNR) is improved by 2 dB?3 dB, and structural similarity (SSIM) is enhanced by 9.3%. Simultaneously, the proposed network has a pretty good restoration impact on degraded images that are influenced by real turbulence.

Underwater visible light communication (UVLC) technology based on a light-emitting diode is a type of underwater wireless communication approach that simultaneously realizes the functions of illumination and communication. UVLC can effectively solve many disadvantages of underwater acoustic communication, such as large delay, small bandwidth, and high energy consumption. However, it reduces the signal-to-noise ratio (SNR) of the receiving plane due to the attenuation of light propagation caused via various media in seawater, degrading the communication quality of the system. Additionally, the concentration of the underwater medium changes as the depth varies, causing the change in the light propagation absorption and scattering coefficient, which affects the parameter setting of the error-correcting coding. In this paper, we use the Monte Carlo approach to implement vertical UVLC channel modeling by operating on the Matlab simulation platform to obtain SNR that contributes to the design of an error-correcting coding scheme based on the polar codes, ensuring that the data transmission is reliable at different channel conditions by adjusting coding parameters. The simulation result shows that the proposed scheme can achieve error-free transmission at different SNRs by adjusting the code rate. Therefore, the proposed scheme can ensure the reliability of the UVLC system by adjusting the coding parameters obtained from the actual channel environment.

Piston aberration in isoplanatic error does not affect imaging quality and requires no calibration; therefore, effective anisoplanatic error should eliminate piston aberration. The approach to compute the piston-removed isoplanatic angle is proposed in this study, which involves measuring double star wavefront error with Shack-Hartmann wavefront sensor. First, the value of the anisoplanatic error in various atmospheric environments is computed using Sasiela and Van Dam analytical expression for angle anisoplanatic error. Thereafter, the process of wavefront error measurement in an actual adaptive optics system with different atmospheric conditions is simulated and the anisoplanatic error is computed using phase screen method. The numerical simulation findings and theoretical calculations are similar. Meanwhile, the correspondence between wavefront error and piston-removed isoplanatic angle is computed. Finally, the anisoplanatic error of double stars is estimated and the piston-removed value of the isoplanatic angle is computed in Lijing 1.8-m astronomical telescope. The finding is confirmed using the approaches of differential image motion and stellar scintillation. The experimental findings exhibit that the piston-removed isoplanatic angle differs slowly in the temporal dimension and rapidly in the spatial dimension, and the importance of the piston-removed isoplanatic angle will be lost with long distance. Based on the approach, the correspondence between wavefront error and piston-removed isoplanatic angle in other atmospheric models and telescopes could be computed and it offers a basis for the location of the beacon.

Observation data of aerosol vertical distribution, particle number concentration, mass concentration, scattering characteristics, and visibility were captured using three-wavelength polarization lidar and online aerosol-monitoring instruments during a dust episode at Shouxian National Climate Observatory from January 14 to 16, 2021. These data, combined with the conventional surface meteorological observation data, were then used for analyzing the stageful evolution characteristics of aerosol microphysics, optical properties, and vertical distribution during the dust episode. The results show that the peak value of the total number concentration of aerosol particles in the transit of dust is 5431 cm-3, the mass fraction peak value of PM10 is 447.2 μg/m3, and the mass fraction ratio between PM2.5 and PM10 is 0.43±0.10. Furthermore, the aerosol spectrum distribution in the dust, haze, and clear-sky stages could be expressed as the superposition of two fine-grained modes and one coarse-grained mode. The number concentration of aerosol particles in the dust stage is significantly higher than that in the haze and clear-sky stages, and the geometric average radius of particles in the two fine-grained modes is basically the same. In the coarse-grained mode, the geometric average radius of particles in the dust stage is 2.24 μm, which is significantly higher than 1.74 μm in the clear-sky stage and 1.79 μm in the haze stage. The average value of the total scattering coefficient in the dust stage is greater than those in the haze and clear-sky stages. In the dust stage, the backscattering ratio of the aerosol particles is found to be smaller, indicating that the air is dominated by larger dust particles. The vertical distribution trend of the aerosol-extinction coefficient at three wavelengths is found to be basically the same, and the extinction coefficient in the dust stage is greater than those in the haze and clear-sky stages. The height of the aerosol layer in the dust stage extends to 3 km near the ground, the depolarization ratio is basically greater than 0.1, and the Angstr?m index is in the range 0.1?0.4.

A parallel simulation method for underwater wireless optical channel simulation is proposed based on open multi-processing (Open MP) and compute unified device architecture (CUDA) to address the computational complexity and low computational efficiency of the Monte Carlo-based model. The simulation calculation efficiency is improved by transplanting computationally intensive parts to threaded parallel computing. Three optimization schemes are introduced to accelerate merging by eliminating invalid photons, limiting high-scattering events, and reducing the amount of data exchange between main and video memories, further improving the simulation efficiency. The acceleration effects in various water types, computing environments, and photon numbers and distances are evaluated. The parallel calculation efficiency of graphics processing units has an acceleration effect of up to 300 times, whereas that of central processing units has an acceleration effect of 90 times compared with traditional serial simulation.

Online monitoring and fault identification of submarine cable are fundamental technology for ensuring the normal operation of cross-sea transmission and communication transmission. To avoid signal distortion due to direct denoising, which affects the extraction of target features, in this paper, the variational mode decomposition (VMD) algorithm is applied to extract features directly from noisy vibration signals. Using the Brillouin optical time domain analysis experimental system for monitoring the submarine cable vibration, the vibration signals of submarine cable under the conditions of anchoring, scouring, and friction are obtained. Three types of vibration signals are divided into 200 groups, and the intrinsic mode function components are obtained using the VMD algorithm. Furthermore, the energy, energy entropy, and kurtosis combinations of each component are obtained as eigenvectors. Using 80% and 20% of the feature vectors as the training and test sets, respectively, the data are classified by inputting them into the support vector machine (SVM) based on the bird swarm algorithm (BSA). The experimental results show that compared with other SVMs, the classification accuracy of BSA-SVM is higher, reaching 99.17%, and the running time is shorter.

Scattering and an uneven distribution of reflected light owing to the target surface texture are the main issues in extracting the structured light strip center in underwater. Herein, we proposed a new approach for underwater information acquisition. In this method, the targets are scanned using structured light for the convolution process, thereby solving the nonuniform distribution of a backscattered background because of nonuniform illumination. Furthermore, the uncertainty of noise fluctuations is reduced from a statistical viewpoint. A virtual aperture method is proposed to eliminate backscattering using this system. Moreover, a method for improving the accuracy of the center extraction is proposed using the restored image to remove the target surface texture, by using the method, conventional center extraction methods can be applied to the underwater targets containing texture, thus widening their application range. Underwater experiments were performed to verify the feasibility and effectiveness of the proposed method.

The applicability of wind profiler radar products in Chengdu is investigated using L-band sounding radar data from the Wenjiang District Weather Station, Chengdu, from January 2020 to July 2020, based on the wind field and atmospheric refractive index structure constant (Cn2). At all levels, there is a significant positive correlation (p-1 smaller than the L-band sounding radar at the low level (-1 smaller than the L-band sounding radar at the high level (>2.5 km), and the effective sample rate of the horizontal wind speed fluctuates between 70% and 90%. Additionally, the effective sample rate of the horizontal wind direction of the wind profiler radar fluctuates growth with increasing altitude. When the atmosphere is moderately unstable, weakly unstable, neutral, or weakly stable, the Cn2 profiles retrieved by the wind profiler radar and L-band sounding radar agree well with each other at the same time. When the atmosphere is severely unstable or moderately stable, the Cn2 profiles retrieved by the wind profiler radar and L-band sounding radar show a significant positive correlation (p<0.05), but the two profiles have a large value difference. Precipitation is another important factor that affects the accuracy of the wind profile radar inversion, resulting in a significant increase in the horizontal wind speed inaccuracy.

Aiming at the phenomenon of color attenuation, surface blur, and uneven illumination in underwater optical images, we proposed an underwater optical image enhancement algorithm based on color constancy and multiscale wavelet. First, we adopt the gray world assumption to compensate the attenuation channel and use the color constancy to adaptively adjust the global brightness and contrast of the image to effectively correct the color shift. Second, combined with the characteristics of multiscale wavelet decomposition, we adopt morphological open operation to improve the dark channel transmittance to remove the low-frequency haze phenomenon, and the soft threshold reduces the high-frequency noise. Then, a two-dimensional gamma function is used to adaptively correct the uneven illumination, and sharpening is used to improve the edge detail. Finally, the weight map of the fused input image is defined: gamma correction and sharpening images, and the enhanced image is obtained by multiscale fusion. The experimental results show that the proposed algorithm can effectively balance the chromaticity and brightness of underwater optical images and significantly improve image clarity and detail information. Additionally, application tests show that the algorithm performs well in feature matching, low-light conditions, and edge detection.

The simultaneous observation of ozone and aerosol in Wangdu County, Hebei Province was conducted using an ultraviolet multi-wavelength lidar to obtain vertical distribution information of ozone and aerosol under combined atmospheric pollution. The results show that atmospheric backscattering causes the largest ozone mass concentration error in the dual-wavelength differential absorption inversion algorithm, with a maximum average mass concentration error of 16 μg/m³. The three-wavelength differential absorption algorithm can reduce the influence of some aerosols. The extinction coefficients of the three lidar wavelengths are eliminated by ozone absorption based on the inversion of ozone mass concentration, and the aerosol extinction coefficients of each wavelength are obtained. Moreover, the aerosol parameter inversion results agree well with the AERONET aerosol optical depth (AOD) data. Finally, UV multi-wavelength lidar inversion results, HYSPLIT backward trajectory analysis, and MERRA-2 reanalysis data were used to examine the typical pollution weather in Wangdu County. By the inversion of ozone mass concentration at 300 m and AOD above 300 m, the changing trend of the two is opposite, and the inhibition effect of AOD on UV radiation is most obvious during midday. During the observation period, air pollution in Wangdu County may be affected by pollutants transported from the northwest.

The mass-specific backscattering coefficient (bbp*) of suspended particles is mainly affected by their composition and sizes. Studying the variation characteristics of bbp* is of great significance to revealing the types and temporal and spatial distribution of such particles in waters and improving the quantitative accuracy of ocean color remote sensing. In this paper, the Mie theory is applied to calculate the bbp* of various common algae and inorganic mineral particles in seawater with different particle size distributions, relative refractive indexes, and apparent densities by simulation. It is found that the average bbp* of inorganic mineral particles is about twice that of algae particles when their particle size distribution slop ξ is the same. When ξ is 4.0, the bbp* of inorganic mineral particles and algae particles at 532 nm are (9.12±3.18)×10-3 m2·g-1 and (4.09±0.48)×10-3 m2·g-1 respectively. The lower bbp* value of algae particles can be explained by the lower real part of their refractive index. Research results of the measured data on the Yellow and East China Seas show that the spatial variability of bbp* is lower than that of the backscattering coefficient. When the mass concentration of inorganic particles is dominant in the total particles, the average bbp*(532) is 8.46×10-3 m2·g-1, which is 2.3 times that, 3.63×10-3 m2·g-1 to be specific, when organic particles dominate. The measured bbp* decreases in the form of power-law function as the mass concentration proportion of organic particles increases. In view of the simulation results, it is concluded that the variation range of the particle size distribution slope ξ of particles in the study waters is 3.6?4.2. In offshore waters dominated by organic particles, ξ is about 3.9. In the vicinity of the Yangtze River Estuary, the bbp* of the suspended particles varies greatly under the influence of the change in the particle size distribution.

To improve the performance of underwater wireless optical communication, a scheme is proposed to increase the bandwidth of underwater optical communication through the multiplexing of vortex beams, and at the same time improve the attenuation length supported by the underwater optical communication by using photon-counting detection. The examination results show that information transmission was achieved in the coastal seawater channel with a slight error rate below the forward error correction threshold, thus verifying the feasibility of the scheme. The transmission power of the communication system is only 3.21 nW after the photon-counting scheme is adopted. Considering only the attenuation of light intensity by the water channel, the supported attenuation length reaches 20.21 in the underwater optical communication system with vortex beam when the transmission power is increased to 1 W. This experiment provides a solution for underwater optical communication that can simultaneously increase the information transfer rate and attenuation length.

We used a microtemperature sensor to measure the atmospheric refractive index structure constant Cn2 of near sea-surface and combined ensemble empirical mode decomposition (EEMD) to obtain the intrinsic mode function (IMF) component with different time scales. Furthermore, the analysis of the IMFs’ periods indicates that their mean periods have a high correlation of natural exponential function. Thus, we can derive the space characters based on the ergodicity property of atmospheric turbulence. The result of the Hilbert transform for the IMF component shows the different scale fluctuations near the center frequency of each IMF. Additionally, we can obtain the Hilbert-Huang transform marginal spectrum of conventional meteorological elements and Cn2, and the results indicate that it is superior to the traditional fast-Fourier transform (FFT) in reflecting spectral distribution characteristics of optical turbulence. Further, we analyze the relationship between the Cn2 and conventional meteorological elements under different atmospheric stratification. From above, we can learn more about the space-time characters of near sea-surface optical turbulence, and the study results will provide some references for laser propagation in the marine atmosphere.

To overcome low detection accuracy, false and leak detections for medium- and small-scale targets, rough segmentation for building boundary of traditional semantic segmentation network, we propose a high-resolution remote-sensing image building change detection method based on deep learning. The proposed method adopts the coding-decoding structure. At the coding stage, the residual network is used to extract the image features. The dilated convolution and pyramid pooling module are introduced in the deepest features of the encoder to enlarge the receptive field and extract the multiscale image features. At the decoding stage, the attention module highlights the useful features, and the features with different scales and resolutions are aggregated. We performed experiments on large-scale remote-sensing building change detection datasets. The results show that the proposed method can obtain deep-layer semantic information and pay attention to detailed information. It also has a considerable improvement in precision, recall, and F1 score. Additionally, the proposed method performs better than other semantic segmentation networks in multiscale target detection and building boundary extraction.

Vehicle-based laser scanning is extensively used for urban three-dimensional data acquisition because of its advantages of fast, high accuracy, and high density. However, it is not easy to accurately and efficiently extract urban road point clouds because of the large amount of data and multiple targets in urban scenarios. Based on the progressive morphological filtering algorithm, this study proposes an algorithm using grid approximation rather than three-dimensional space point operation and adaptive calculation of filtering parameters. As per the spatial distribution characteristics of urban roads, using the driving track information of scanning vehicles, the road boundary points are extracted using normal vector clustering, distance constraint, and continuity distribution constraint methods. Moreover, the accurate road boundary is generated by result clustering and fitting to achieve fast and accurate extraction of the road point cloud. The experimental results demonstrate that the accuracy, integrity, and overall quality of the road boundary extracted using the proposed algorithm are >90%. This shows that the difference between the boundary position and detected value is <3 cm.

Herein, a method of post-processing filtering based on space vector projection is proposed to eliminate the near-ground points that have a considerable impact on the accuracy of digital elevation model (DEM) construction to address the problem of difficulty in generating a high-quality DEM via single progressive morphological filtering for airborne light detection and airborne ranging (LiDAR) data. Initially, the proposed method takes each laser point as starting point and then constructs vectors with the lowest laser point of each of the nine grids closest to it at the end. Thereafter the method accumulates the projection of each of the nine vectors in the Z direction, compares the results to the preset threshold, and identifies as well as classifies the laser point. To validate the effectiveness of the proposed method, this study selects six groups of test data from the international society for photogrammetry and remote sensing (ISPRS) under different terrain conditions and generates 1 m × 1 m resolution DEM using ground points extracted before and after the post-processing filtering as well as performs linear fitting with reference DEM in the same research area. The results show that when compared with a single progressive morphological filtering algorithm, the combined algorithm of progressive morphological filtering and post-processing filtering based on space vector projection can achieve higher precision of point cloud filtering and DEM construction in urban area and rural area with continuous terrain as well as has good applicability and reliability.

Input with the effects of the ocean's actual atmosphere, such as temperature, humidity, and wind, on the distribution characteristics of transmittance between 3-5 μm and 8-12 μm are quantitatively discussed using the radiative transfer model. The effects of different paths and the cloud type cover on the results of transmittance are also investigated. Results show that the regional and seasonal changes of atmospheric temperature, humidity, and other parameters are obvious, thereby directly affecting the calculation result of radiative transmittance. The establishment of a local atmospheric parameter model plays an important role in the calculation of atmospheric radiative transfer for photoelectric engineering.

One of the gases responsible for the greenhouse effect is carbon dioxide (CO2). For climate prediction, human production, and human life, the spatial distribution of CO2 concentrations must be considered. Controlling the spatial and temporal distribution of CO2 worldwide requires an accurate inversion of CO2 concentrations. However, in the near-infrared band, surface reflectance uncertainty affects the inversion of CO2 concentration. The ratio method is introduced to process the satellite ground-to-ground radiation spectrum, and it is verified that the absorption band radiance ratio and CO2 concentration are related; moreover, inverting the CO2 concentration using the relationship is feasible. The data source was the MODTRAN4-simulated radiation spectrum, and the four absorption peaks' spectral radiance ratio and CO2 concentrations were selected for analysis. The results show that the spectral radiance ratio and CO2 concentration have an approximately linear relationship, and the linear relationship is evident at 6310 cm-1, with an error of only 1.15%. The ratio of radiance ratio to concentration is further investigated using various atmospheric and aerosol models. The results show the radiance ratio and concentration are highly correlated in the range of 0.1-0.9 reflectivities, the correlation coefficient is up to 0.98, and the average error is less than 2%. The measured data is subjected to the same processing as the simulation data, and the results are compared with simulated data. The linear relationship at 6334 cm-1 is the best among the four bands, and the linear relationship reaches 0.99. It shows that the spectral radiance ratio and CO2 concentrations have a linear relationship, and this relationship can be effectively applied to the inversion of CO2 concentration, effectively eliminating surface reflectance.

This study retrieves the aerosol extinction coefficient, the height of the boundary layer, and the mass concentration of ozone based on differential absorption lidar. Through the atmospheric temperature profile, ground meteorological elements, and air quality data, backward trajectory and naval aerosol analysis and prediction system, a heavy pollution process in Wangdu County is analyzed. Experiment results show that during the observation period, Wangdu County is under the control of the East Asian trough system, and there is always a temperature inversion layer within 100?200 m of the surface layer. When particulate pollution is severe, the relative humidity on the ground is high, the wind speed is low, and there is a weak downdraft at high altitude, which is conducive to the moisture absorption growth and long-term accumulation of particles. The boundary layer height is always low, which is not conducive to the diffusion of pollutants. In addition, the boundary layer height has no obvious correlation with the particle mass concentration, but it is negatively correlated with visibility, and the correlation coefficient is -0.344. The mass concentration of ozone is positively correlated with temperature and visibility and negatively correlated with relative humidity, boundary layer height, and wind speed. The local quiet and stable weather and the transmission of pollution sources from other places are the major causes of air pollution in Wangdu County.

Based on the generalized Huygens-Fresnel principle, the spectral density, degree of coherence, and the coherent vortex of partially coherent elliptical vortex beam propagation through anisotropic non-Kolmogorov turbulence are studied. Among them, we focus on the important properties of coherent vortex beams as partially coherent vortex beams. It is found that the elliptic rate, coherence length, and turbulence parameters all have influences on the conservation distance. Moreover, it is easier to separate the newly generated coherent vortex points of partially coherent elliptical vortex beams than that of partially coherent circular vortex beams.

In view of the high complexity and low detection accuracy of the existing visibility detection methods, a road visibility detection method based on monitoring images is proposed in this work. First, the transmittance of dark and bright primary colors is obtained by using the prior theory of dark and bright primary colors; then, the atmospheric light value and atmospheric transmittance are optimized by using adaptive defogging weight and adaptive filtering window, and the transmittance of the front and rear ends of the lane line is one-to-one corresponding to that of the optimized transmittance of dark and bright primary colors; finally, the atmospheric extinction coefficient and visibility are calculated by combining the distance between the front and rear ends of the lane line. Experimental results show that the method can achieve high precision detection within 100--600 m, and the relative error is less than 10%. Compared with other methods, the method has faster detection efficiency, higher accuracy and easier implementation.

Using atmospheric turbulence transmission theory and partially coherent light cross spectral density function， the coupling efficiency of partially coherent light-fiber array is studied， and the influences of light source coherence， lens array sub-aperture number N， transmission distance， turbulence intensity， and wavelength on coupling efficiency are analyzed in this paper. Simulation results show that the lens array can well restrain the decrease of the coherence degree of the light source and the influence of atmospheric turbulence on the coupling efficiency of partially coherent light-fiber array. When the equivalent receiving aperture is the same， the increase of the N of the lens array can effectively improve the coupling efficiency of partially coherent light-fiber array. When N=37 and the transmission distance is greater than 3 km， the coupling efficiency curve tends to be stable. For a light source with a wavelength of 1550 nm and a coherence of 0.04 m， compared with single-lens reception， the lens array with N=37 can increase the coupling efficiency from 40% and 8% to 60% and 53% respectively in the case of moderate and strong turbulence. Compared with the long-wavelength light source， the coupling efficiency of the lens array to the short-wavelength light source is improved more obvious. For light sources with wavelengths of 850 nm and 1550 nm and a coherence of 0.04 m， compared with single-lens reception， the lens array with N=37 can increase the coupling efficiency from 18% and 41% to 57% and 60%， respectively.

The existence of atmospheric turbulence and platform micro-vibration will cause the random channel attenuation of the satellite-to-ground laser communication links， which leads to the unstable communication quality. To further analyzes the performance of satellite-to-ground laser communications with the influence of atmospheric turbulence and platform micro-vibration， a random attenuation model of joint satellite-to-ground laser link is established. Based on binary phase shift keying modulation and heterodyne coherent reception， the closed form expression of system average bit error rate under the model is given. The influence of different satellite-to-ground laser communication system parameters on the bit error rate performance is analyzed by simulation. The research results can provide a theoretical reference for the design of practical satellite-to-ground laser communication system.

The inversion method of temperature and pressure from the upper and middle troposphere to the lower stratosphere is studied and simulated. An absorption line is selected， which is not sensitive to temperature but sensitive to pressure， and the relationship among the absorption cross section， pressure and the absorption coefficient is used to determine the pressure by using the iterative method. An absorption line is selected near the weak absorption peak and the relationship among the absorption coefficient， pressure and temperature is used according to the retrieved pressure value to determine the temperature by using the iterative method. In order to reduce the influence of other absorption and scattering factors on the inversion results， the simulation process adopts the method of differential wavelength. In the oxygen absorption band， the appropriate absorption line is selected， and the profile of the differential absorption coefficient at the tangent altitude of each laser track is obtained by retrieving the simulated data of the laser occultation differential transmittance from the Abel integral inverse transformation， and then the pressure and temperature at each tangent altitude are retrieved using the differential absorption coefficient. The simulation results show that the inversion error of pressure is primarily affected by the inversion error of the differential absorption coefficient， which increases with altitude decreasing， and the maximum error is approximately 6%； the inversion error of temperature is affected at the same time by the inversion error of pressure and the differential absorption coefficient； the two influences are partially offset， and the maximum error is 1.5 K near an altitude of 5 km. Through analysis of the error model， some change trends and influence factors in the inversion error are explained. Under the condition of eliminating the inversion error of the differential absorption coefficient， the pressure and temperature are solved once in a cycle， the maximum inversion error of pressure is approximately 0.3%， and the temperature is approximately 1 K. The comparison between this inversion error and the inversion error of the differential absorption coefficient highlights the importance of reducing the latter.

Aerosol optical depth （AOD） is a key factor for characterizing aerosol content and atmospheric pollution. In this study， level 2 aerosol profile products of the CALIPSO satellite were used to analyze the temporal and spatial variation characteristics and trends of AOD in specific regions worldwide from 2009 to 2018. Results show that AOD has a certain temporal and spatial difference in different areas. On the spatial scale， high AOD value centers are mainly distributed in India， Saudi Arabia， and other regions； moreover， on the temporal scale， noticeable seasonal differences exist. Specific regions such as India， Saudi Arabia， and northern China show peak AOD during the MAM and DJF periods， while Brazil peak during the JJA period. Moreover， significant AOD trend differences exist in each typical region， with the strongest upward trend in India.

In road network extraction using airborne LiDAR point clouds, the road intensity inconsistency issue results in more points similar to road intensity when using intensity to extract roads, and some real road points are also filtered out. In this paper, we propose a grid segmentation method for extracting road point clouds based on local intensity. The method first uses skewness balance to obtain the road-intensity threshold of the filtered ground points, divides the ground points into a grid, and calculates the grid’s average intensity value. The number of grids for intensity values of the central grid and its neighboring grids within the road-intensity threshold is used to calculate the road point cloud. Experiments conducted with actual data in a complex environment show that the method can effectively reduce the abnormal points around the road while obtaining a more complete road, providing reference for future road network extraction. Data1 in the extracted initial road has a completeness rate of 84.1%, and data2 has a completeness rate of 67.1%, which has obvious benefits compared with the traditional method.

The sun glint on the water surface leads to flares in the optical images and loss of ship target detail information. This paper presents a method of suppressing sun glint on water surface by combining polarization filtering and polynomial fitting. In an imaging optical path, a polarizer is used to filter the glint based on the polarization characteristics of sun glint reflected from the water surface, and the glint areas in the polarization filtering images are estimated through polynomial fitting estimation. The water surface glint polarization imaging experimental device lint is constructed, and the polarization filtered image of the water surface glint is acquired. Polynomial column direction curve, row direction curve, surface, and line-by-line polynomial curve fitting methods based on the least square method are used to process the polarization filtered image. The experimental results show that using a polarization filter in conjunction with a line-by-line polynomial fitting method can effectively remove the sun glint while also making the processed image brightness more natural, not including saturated pixels and highlighting the details of the ship targets.

The detection of nearshore wave period is crucial for fine nearshore wave forecast. Thus, we propose a novel method to realize automatic detection of nearshore wave period by learning spatiotemporal features from nearshore wave surveillance videos. The method takes continuous ocean wave video frames as inputs. First, a two-dimensional convolutional neural network (2D-CNN) is used to extract spatial features of the video frame images, and the extracted spatial features are spliced into sequences in the time dimension. Then a one-dimensional convolutional neural network (1D-CNN) is used to extract temporal features. The composite convolutional neural network (CNN-2D1D) can realize the effective fusion of wave space-time information. Finally, the attention mechanism is used to adjust the weight of the fusion features and linearly maps the fusion features to wave period. The method in this paper is compared with the detection method only extracting spatial features based on VGG16 network and the detection method for spatiotemporal feature fusion based on the ConvLSTM and three-dimensional convolutional (C3D) network. The results of experiments show that C3D and CNN-2D1D achieve the best detection results, with an average absolute error of 0.47 s and 0.48 s, respectively, but CNN-2D1D is more stable than C3D, with a lower root-mean-square error (0.66) than C3D (0.81). And CNN-2D1D requires fewer training parameters. These results show that the proposed method is more effective in wave period detection.

In this paper, the light intensity scintillations of plane wave and spherical wave are analyzed and compared for providing references for engineering design and performance evaluation of the optics system employed in turbulence medium. First, based on the classic weakly fluctuating turbulence theory, the analytical expression of the light intensity scintillation at aperture reception is derived. Then, based on the extended Rytov theory, the light intensity scintillation under nonweak fluctuation conditions is calculated. Finally, the light intensity scintillation of plane and spherical waves is simulated under various turbulence intensities and Fresnel numbers. The results show that when the Rytov variance is less than 4.8, an intersection point is present between the light intensity scintillation curves of the plane and spherical waves. The intensities of the plane and spherical wave scintillations under the Fresnel number corresponding to the intersection point are equal. When the Rytov variance is greater than 4.8, the light intensity scintillation of the plane wave is always less than that of the spherical wave. This research is of great significance for designing optical transceiver antennas and selecting beam wavelengths and waveforms in wireless optical communication systems.

The Qingcaosha reservoir at the Yangtze River estuary is an important source of drinking water, and its water quality must be assessed. This paper takes suspended solids in the water body as a key parameter to evaluate water quality and conducts related research using high spatial resources data of Landsat-8 Operation Land Imager (OLI) to objectively and scientifically evaluate the water quality of Qingcaosha reservoir. An inversion algorithm for suspended particulate matter (SPM) in Qingcaosha reservoir was developed using satellite data and field observations. Field observations were used to verify the accuracy of the developed algorithm. The results showed that the correlation coefficient was high and the root mean square error was low, indicating that the algorithm is effective. In addition, the inversion accuracy is high and the inversion result is credible. The Landsat-8 OLI data from 2013 to 2019 were processed using the proposed algorithm to obtain the average spatial distribution and time distribution characteristics of SPM. The SPM concentration in Qingcaosha reservoir was found to be the lowest in the estuary. The difference of SPM concentration in the reservoir’s upper part is the largest in winter and the smallest in spring. The concentration of SPM in the reservoir’s middle and lower parts is low, and the change is small. According to the research results, the Qingcaosha reservoir at the Yangtze River estuary is clean and has good water quality.

Atmospheric optical turbulence is the fundamental parameter closely related to the design and application of optoelectronic systems. The field measurements of atmospheric optical turbulence profiles by instruments are limited by labor, materials, financial resources, and other conditions. Therefore, it is of great significance to estimate the intensity of atmospheric optical turbulence according to the conventional meteorological parameters. A back propagation combined with genetic algorithm (GA-BP) neural network is proposed.First, based on Tatarski atmospheric optical turbulence parameterization scheme, the HMNSP99 outer-scale model is used to estimate the optical turbulence profiles; second, attempting to construct BP artificial neural network combined with genetic algorithm, which are trained by measured data to predict atmospheric optical turbulence profiles. The atmospheric optical turbulence profiles estimated by the two methods are compared with the measured profiles. The results show that the root mean square error (RMSE) between the estimated values of GA-BP neural network and measured values is smaller than that of HMNSP99 model, which proves that it is a feasible method to use GA-BP artificial neural network model to estimate the optical turbulence profiles.

In order to better suppress the influence of solar flare on sea surface target detection, a sea surface solar flare suppression method is proposed based on polarization detection technology and the difference of polarization characteristics among background water body in this paper, solar flare and typical marine targets. The effects of observation zenith angle and solar zenith angle on the polarization of sea surface targets under the background of the solar flare and the contrast between sea surface targets and solar flare background are analyzed. The results show that when detecting sea surface targets in sunny weather, the background radiation is mainly affected by the irradiance caused by the direct reflection of solar radiation from the sea surface. There is no significant difference between the visible light wavelengths of 550 nm and 670 nm in the inhibition effect of solar flare. The inhibition effect of solar flare is better when the observation zenith angle is near 53°, 50°--60° solar zenith angle direction and the sum of solar zenith angle and observation zenith angle is about 106°. This research is of great significance to improve the contrast between the sea surface target and the solar flare background image and the target detection effect under the sea surface solar flare background.

Scene classification of high-resolution remote sensing image is one of the important tasks in interpreting remote sensing image information. In order to extract the target information accurately, we propose a high-resolution remote sensing image scene classification method based on salient features combined with deep convolutional neural network (DCNN) to solve the problems of complex background, diverse targets, and difficult to distinguish between target information and background information in the classification of high-scoring remote sensing image scenes. First, K-means clustering algorithm and super-pixel segmentation algorithm are used to generate the color spatial distribution map and color contrast map of the image, and the different contrast maps are fused to get the saliency map. Then, the features in the saliency map are enhanced through logarithmic transformation, and the adaptive threshold segmentation method is used to improve the discrimination of the target and divide the target area and the background area, and extract the area of interest. Finally, a DCNN model is constructed to extract deep semantic features and classification, and the obtained features are input into the network model for training and classification. Experimental results show that the method can effectively distinguish the main target information from the background information and reduce the interference of irrelevant information. The classification accuracy of the method on the UC-Merced data set and WHU-RS data set are 96.10% and 95.84%, respectively.

Aiming at the inversion of suspended particulate matter (SPM) concentration using hyperspectral data, this paper proposes a supervised band selection method based on pre-trained neural networks (PNNs), and employs the random forest and neural network to establish an inversion model of SPM concentration. The PNN method needs to perform multiple repeated experiments to obtain sufficient and low-noise expression of band importance. In each experiment, an appropriate number of bands is selected as the features of input data of neural networks. Then, we train a neural network and obtain weights of the first layer in the last training epoch. Finally, we use the L1 norm, L2 norm, and ReLU (Rectified Linear Unit) function of the weights to represent the importance of the bands. The experiment results show that the PNN method using L1 norm and L2 norm can obtain a more informative band set, and perform better when used for SPM concentration inversion.

Humidity correction on atmospheric extinction coefficient is an important component of aerosol hygroscopicity research, which is also a key technical link for determining the mass concentration of near-ground particulate matter retrieved by satellite aerosol optical depth(AOD). Based on hourly PM2.5 mass concentration, atmospheric visibility, and relative humidity (RH) data collected in Chengdu from January to December 2016, the statistical relationship between the atmospheric extinction coefficient and particulate matter mass concentration, as well as its response characteristics with RH variation, are discussed in detail. The atmospheric extinction coefficient per unit mass follows a log-normal distribution when RH is less than 90%, and the shape and scale parameters of the distribution function exhibit a fluctuating growth as RH increases. Second, based on the log-normal distribution parameter of atmospheric extinction coefficient per unit mass under dry environmental conditions (RH ≤ 40%), the effect of humidity change on the probability distribution parameter of atmospheric extinction coefficient per unit mass is eliminated via mathematical transformation. Consequently, the principle and flow chart of humidity correction are proposed for the atmospheric extinction coefficient. Finally, the applicability based on the principle demonstrates that the correlation coefficient of PM2.5 mass concentration calculated by corrected atmospheric extinction coefficient and actual PM2.5 mass concentration is up to 0.90, significantly improving the corresponding humidity correction result using aerosol scattering hygroscopic growth factor method.

In this study, using the extended Huygens-Fresnel principle and the improved Rytov method, a turbulence channel model based on the Gamma-Gamma intensity probability distribution is used to obtain the analytical expression of outage probability. On this basis, the outage probability characteristics of the heterodyne differential phase-shift keying (DPSK) modulation of Gaussian beam waves are studied in anisotropic turbulence. A performance study under different anisotropic ocean turbulence conditions is conducted. The effects of various turbulence parameters, i.e., the contributions of temperature and salinity to the power spectrum, the dissipation rate of kinetic energy per unit mass fluid, and the dissipation rate of mean-squared temperature, are investigated, and the transmission distance and data transmission rate on outage probability are analyzed. The analysis provides a theoretical basis for reducing the outage probability of Gaussian beam DPSK modulation and improving communication quality and reliability.

Cirrus optical thickness is one of the cloud optical parameters that have great influence on global climate and earth radiation budget. In military, atmospheric science and other fields, there is a wide demand for cirrus optical parameter solving algorithm. Moderate-resolution imaging spectroradiometer (MODIS) data is used to solve cirrus parameters, and satellite multi-channel data is mostly used, so the data processing process is relatively complex. The RT3 model combined with MODIS cloud parameters was proposed to simulate and calculate cirrus reflectance, and a cirrus optical thickness lookup table was established. A simple algorithm was designed to achieve effective inversion of cirrus optical thickness. The correlation coefficient between the inversion results of cirrus optical thickness and the actual data measured by MODIS is 0.97, which verifies the reliability of cirrus optical thickness inversion. By selecting MODIS data at different time periods, the variation of cirrus optical thickness in different time and space ranges is analyzed, and the average error is less than 0.16, which further verifies the effectiveness of the RT3 model-based lookup table for inversion of cirrus optical thickness. The results are helpful to realize simple and effective inversion of cirrus optical properties worldwide.

Based on an in-depth investigation on the randomness of the time series of the atmospheric extinction coefficient, this paper uses the monitoring data of atmospheric visibility, relative humidity (RH), the mass concentrations of particulate matter (PM10 and PM2.5), and NO2 content during autumn and winter in Chengdu from 2015 to 2017. In addition, the time series of the aerosol extinction coefficient in the corresponding period in Chengdu is obtained. The detection of nonstationarity in the aerosol extinction coefficient time series is conducted using generalized additive models for location, scale, and shape, followed by the covariate analysis of the aerosol extinction coefficient time series. The experimental results show that the aerosol extinction coefficient time series in Chengdu during autumn and winter are nonstationary, with nonlinear changes in their mean and variance. The mass concentration of fine particulate matter (PM2.5), RH, and aerosol component structure (PM2.5/PM10) are significant covariates of nonstationarity in the aerosol extinction coefficient series. Among them, PM2.5 contributes the most to the nonstationarity of the aerosol extinction coefficient series, followed by RH, and PM2.5/PM10 contributes the least. The explosive growth of aerosol extinction coefficient is closely related to the synergies of PM2.5, RH, and PM2.5/PM10.

To evaluate the effects of aerosol radiation forcing and laser atmospheric transport, it is necessary to know the parameters of aerosol light absorption characteristics and its vertical distribution. Thus, this paper presents a method based on a combination of field measurements and models to estimate the aerosol absorption coefficient distribution at vertical height. With the proposed method, the aerosol optical depth (AOD) and extinction profile at the entire layer are obtained via inversion with data observed using a sun-photometer and a LiDAR. Then, the aerosol absorption profile is obtained via selecting the corresponding aerosol modes as constraints from the moderate spectral resolution atmospheric transmittance algorithm and computer model (MODTRAN) and santa barbara DISORT atmospheric radiative transfer (SBDART) model. An inversion test is performed using data measured in a field experiment, and the results demonstrate that the proposed method is feasible and can be employed to obtain the vertical distribution of the aerosol absorption coefficient.

Cloud pollution can easily decrease the accuracy of satellite infrared hyperspectral observation data, leading to the loss of a large amount of observation information. In this study, a method for retrieval of temperature profile on the cloud is proposed based on observation data of FY-4A/GIIRS with cloud conditions. The radiative transfer model is used to carry out simulation experiments of observation brightness temperature under conditions of clear sky and cloud, respectively. We statistically analyze the characteristics of simulated brightness temperature changes under different channels, determine the channel selection scheme according to the cloud top pressure, and realize the retrieval of the temperature profile on the cloud through the neural network algorithm. The ERA5 reanalysis data is used as the reference standard in the accuracy evaluation of the temperature profile retrieval. The experimental results show that the overall root mean square error is better than 1.5 K, and the retrieval temperature profile has a high accuracy, which effectively improves observation data usage rate of the FY-4A/GIIRS in the cloud under pollution.

Many organisms have developed the ability to navigate using polarized ultraviolet light of the sky. The energy and polarization of the ultraviolet (UV) band of skylight are much lower than those of the visible light, yet organisms utilize the UV band for navigation; this phenomenon is known as the "ultraviolet paradox of biological polarized light navigation". To explore the advantages of skylight polarization in the UV band, we first analyzed the single-particle scattering law based on the Mie scattering theory, studied the light transmission characteristics of clouds using the Monte-Carlo method, and finally completed the simulation of the full-sky polarization mode. The simulation results show that the UV band has a higher polarization retention after penetrating the cloud layer, and can still be used to complete navigation in unfavorable weather conditions such as cloudy and overcast skies. In this study, we demonstrate why the UV band in skylight polarization navigation is advantageous. Furthermore, the analysis of our hypothesis and study results provide guidance for the selection of the target waveband for bionic polarization navigation.

The traditional YOLOv3 model uses ImageNet and COCO datasets for training, in which the scene target characteristics are significantly different from those in test datasets, and leads to low detection accuracy of complex scene targets in high-resolution remote-sensing images. This paper optimizes the training process of the traditional YOLOv3 network using the idea of transfer learning. During the training of the YOLOv3 network, the model is pre-trained by generating an augmented dataset similar to the target domain. The training-optimized method improves the accuracy of the object boundary of target prediction. Also, the parameters of the pre-training model are fine-tuned using a training dataset from the target domain, thus, completing the whole training process of the network. The experiment on the detection of three types of object, including aircraft, playground, overpass, was carried out based on a subset of RSOD & DIOR dataset for remote sensing image object detection. The results show that the proposed YOLOv3 model effectively improves the detection accuracy of the three types of targets in complex urban scenes. The mean average precision of object detection using our model improved by 2% or more, compared with the traditional YOLOv3 model.

To ensure the real-time performance of the nonuniformity correction of the complementary metal-oxide-semiconductor (CMOS) image sensor in aerospace remote sensing cameras and reduce the photo response non-uniformity (PRNU) of the image, according to the structural characteristics of the CMOS image sensor, a CMOS image non-uniformity correction method based on an adaptive moving window is proposed in this study. First, from the perspective of engineering applications, a movable variable-step window is used to block the image so that multiple columns of pixels in the same window shared a set of correction parameters. Then, to solve the problem of insufficient linear fitting correction accuracy in existing methods, based on the nonlinear response characteristics of the CMOS sensor, the response curve is second-ordered by the least squares method. Experimental results show that the method can not only improve the quality of CMOS images but also reduce the number of correction parameters of the hardware system. The PRNU of the image corrected by the method is less than 1%. Compared with the linear fitting correction method, the number of correction parameters of the method is reduced by 23.7%.

In order to solve the problem that the detection of thin clouds and broken clouds is very difficult due to the changeable cloud shapes in the research of cloud detection in RGB color remote sensing images, a U-shaped network based on multi-scale feature extraction (MS-UNet) is proposed. Firstly, a multi-scale module is proposed in order to obtain a larger receptive field while retaining more semantic information of the image. Secondly, the FReLU (Funnel Rectified Linear Unit) activation function is introduced in the first group of convolutions to obtain more spatial information. Finally, further feature extraction is performed after down-sampling, and in the up-sampling pixel recovery, the missing information is completed by jump layers, and the deep semantic features of the cloud are combined with the shallow detail features to achieve better cloud segmentation. Experimental results show that this method can effectively segment thin clouds and broken clouds. Compared with UNet, MF-CNN, SegNet, DeepLabV3_ResNet50, and DeepLabV3_ResNet101 networks, the overall accuracy is increased by 0.075, 0.065, 0.070, 0.013, and 0.005, respectively.

To improve the ability of ResNet50 to extract target object features of remote sensing scene images and interpretability of scene classification, a Resnet50-CBAM-FCAM(RCF) network-based method of remote sensing image scene classification is proposed in this paper. This method increases the convolution attention module and full convolution-class activation mapping branch in the ResNet50 network. With the help of an attention mechanism, the branch features are fused with the extracted channel attention features and spatial attention features, respectively, and the class activation maps of various scenes are generated. The experimental results show that the overall classification accuracy of the proposed method in AID and NWPU-REISC45 datasets is more than 96% and 93%, respectively, and the visual results of the class activation maps can focus the target objects of remote sensing scene image accurately.

Water depths are the basic data for surveying and mapping seabed topography, which is of great significance for marine scientific research. A diffractive optical system has the advantages of small size and light weight, and a conformal design can reduce the impact of the load on the aerodynamic performance of an aircraft, which is conducive to the formation of a large optical aperture. This paper introduces the system scheme and parameters of airborne bathymetry lidar based on a large-aperture receiving conformal diffractive optical system. The narrow bandwidth characteristic of the diffractive optical system is used to suppress the received background light noise. To realize both direct and coherent detection methods, the seawater depth detection of airborne lidar is analyzed based on the minimum detectable signal-to-noise ratio. The results demonstrate that when the receiving aperture is 0.6 m, the instantaneous receiving field of view is 50 mrad, the average transmitting power is 50 W, the detection depth of the system in the direct detection mode during the day is 69 m, and the detection depth in the coherent detection mode is 86 m.

This study investigates the performance of the hybrid free space optical/radio frequency (FSO/RF) communication system based on the selective combination technology under the conditions of the Málaga turbulent channel and the Nakagami-m fading channel. Considering the pointing errors, we deduce the expressions of the average bit error rate and the outage probability of the hybrid FSO/RF system that adopts the subcarrier modulation and intensity modulation direct detection scheme. Their closed-form solutions are then obtained using the Meijer G function and the extended generalized bivariate Meijer G function. The bit error rate and the outage probability performances of the hybrid FSO/RF and only-FSO systems are investigated under different subcarrier modulation schemes, turbulence intensities, pointing errors, and RF channel fading parameters. The simulation results show that compared with the only-FSO system, the hybrid FSO/RF communication system can effectively improve the communication system performance.

The sound wave movement can change the surrounding atmospheric pressure and further affect the atmospheric refractive index distribution. Based on the wave equation and superposition principle of acoustic waves and the calculation formula of atmospheric refractive index, this paper solves the spatial distribution of artificial atmospheric refractive index heterogeneous body excited by point-array coherent sound source. Based on the Rytov approximation, the numerical relationship between the pressure excited by the point-array coherent sound source and the light wave flicker index is given, and the influence of the change of the point-array coherent sound source parameters on the light wave scintillation index is analyzed. The results show that the sound source can excite the uneven refractive index of the atmosphere, causing light intensity fluctuations. Changes in various parameters of the sound source can cause fluctuations in the light wave flicker index to varying degrees. The research results in this paper have preliminary explored the influence of array coherent acoustic waves on the laser transmission characteristics under the condition of artificial atmospheric refractive index heterogeneous body.

Based on the references of average aerosol extinction coefficient per unit mass concentration in dry environment and baked aerosol scattering extinction coefficient in wet environment respectively, corresponding the two kinds of aerosol extinction hygroscopic growth factor, i.e. f1(RH) and f2(RH), had been proposed. By utilizing the hourly data from nephelometer and aethalometer, as well as the coincidental environmental and meteorological data, including atmospheric visibility, relative humidity, NO2 mass concentration, and PM10 mass concentration, in Chengdu from October 2017 to December 2017, the comparative study on the two kinds of aerosol extinction hygroscopic growth factors was systematically carried out. The results showed that both f1(RH) and f2(RH) could well characterize the optical effect of aerosol hygroscopicity, and their coefficient of determination was 0.90 (passed the significance test of α=0.01). By multi-model comparison, the quadratic polynomial function was proved to best fit the variation of both f1(RH) and f2(RH) with relative humidity. The ratio of average f1(RH) to average f2(RH) increased with the increase of relative humidity. Further research indicated that the significant response of baked aerosol scattering extinction coefficient to the variation of relative humidity was fundamental for the above inconsistency between f1(RH) and f2(RH).

In this work, an automatic power line extraction method based on airborne LiDAR point cloud data is proposed. First, spatial partitioning of LiDAR data was performed. Second, according to the horizontal distribution characteristics of power lines in three-dimensional space, an improved Euclidean clustering algorithm was used to realize rough extraction of the power lines. Third, using the connection between a power line and a power tower, the spatial coordinate position at the top of the power tower was estimated. Then, the improved Euclidean clustering algorithm was used to realize single power line extraction, and the model was used to combine a straight line and parabola to obtain the centerline equation of a single power line and its radius. Finally, a power line adapter was developed at the insulator according to the power line equation and radius, and the complete point cloud of a single power line was obtained. Experiment results show that compared with the classification effect of support vector machines combined with the geometric feature method, the proposed method can extract complete power lines automatically, quickly, and accurately from power line inspection data, which has application value in power patrol.

Atmospheric coherence length is an important parameter for evaluating the effect of adaptive phase correction in a laser transmission system, so there is a high research value to measure and analyze the atmospheric coherence length. In this paper, a system for measuring atmospheric coherence length by differential image motion method is designed and built to carry out field experiments in Xi'an area, and the variation trend of atmospheric coherence length within the whole day in Xi'an area is analyzed. Results show that although the values of atmospheric coherence length measured in different directions are different, the overall variation trend is the same, and the variation is more stable at night than at day. These results have a reference value for the construction of urban wireless optical transmission systems.

The atmospheric environment seriously affects performance of the free space optical communication system. Considering the influence of weather environment, atmospheric turbulence and directivity error on laser communication, we establish a joint channel statistical model, and derive the performance parameters of free space optical communication system based on on-off keying modulation, such as average bit error rate, average channel capacity and outage probability and their closed expressions, using Meijer-G function. The performance parameters of the system are simulated and analyzed under different M turbulences, different normalized pointing errors and visibilities of 5 km and 20 km. The results show that the smaller the directivity error, the greater the influence of turbulence on the performance parameters of the communication systems; the bigger the directivity error, the more likely for a best beam divergence angle existing to make the communication system achieve the best performance.

Combined with Sahu-Shanmugam and Fournier-Forand volume scattering functions, a simulated model of underwater laser transmission channel is built with Monte Carlo method, and the model is used to analyze the beam extension characteristics at the receiving end. The effects of received field of view and the diameter of receiver on the power density of the beam, and the distribution characteristics of beam power density under different receiving distances are studied under three typical waters. The results show: with the increase of scattering coefficient in the water area and the increase of transmission distance, the beam distribution expansion is intensified; with the increase of diameter of receiving surface, the variation trend of the beam power density decreases gradually, and the amplitude of the beam power density increases as the increasing receiving field angle; with the increase of transmission distance, the distribution of beam power density becomes more discrete. The results provide a reference for underwater positioning or underwater receiver design.

Lidar and stereo cameras are important environmental sensors for unmanned driving. Calibrating external parameters between these two sensors is an important basis for their combination; however, combining two types of information requires a complex calibration process. This paper proposes a method based on feature point pair matching. Two rectangular planks are used to extract the 3D point cloud of the edge of the board in stereo vision and lidar coordinate systems, which is then used to obtain the corner coordinates. Finally, the Kabsch algorithm is used to solve the coordinate transformation between the paired feature points, and a clustering method is used to remove outliers from the multiple measurements and obtain the average value. By setting up an experiment, this method can be implemented on the Nvidia Jetson Tx2 embedded development board, and accurate registration parameters can be obtained, thus verifying the theoretical method’s feasibility. This registration method is simple and easy to execute, can automatically perform multiple measurements, and is improved compared with similar methods.

Fine mode aerosol optical depth in Xianghe was calculated, using data from the onboard multi-angle polarization sensor POLDER-3 in the PARASOL satellite. The retrieval results were compared with the operational products of POLDER, MODIS, and AERONET data. The results show that the accuracy of POLDER using polarization remote sensing is significantly better than that of unpolarized MODIS. The correlation coefficient is increased from 0.67 to 0.93, and the average error is reduced from 0.32 to 0.15. As combined with the neural network (NN) method, the method gave correlation coefficient of 0.94 and standard deviation of only 0.11. Then, NN was applied to Hangzhou and Hong Kong, respectively. The verification results show that it has similar accuracy in Hangzhou but poor applicability in Hong Kong. The research shows it is feasible to use the NN to extract fine mode aerosol information from polarized signals.

In order to make the resolution of segmented telescopes close to the diffraction limit of equivalent aperture, each sub-mirror must have extra high coplanar precision. In this paper, aiming at the co-phasing problem of segmented telescopes, first, the principle of co-phasing detection technology of pupil plane and focal plane in segmented telescopes optical co-phasing detection technology is studied. Then, the advantages and disadvantages, application fields and future development trends are summarized. Finally, solutions are provided on the detection problems of large piston error and large tip-tilt error respectively.

When using linear quadratic Gaussian (LQG) control on each mode, the higher-order disturbance model not only requires non-negligible identification effort but also leads to the calculations of high-order control matrix, which greatly increases the computational burden of the real-time processor. To address this problem, we propose a hybrid control method for adaptive optics (AO) system, which is feasible from an implementation viewpoint. This method combines the optimal modal gain integral control (OMGI) and LQG control algorithm, and designs the control strategy of the corresponding mode according to whether the mode is affected by narrow-band disturbances. The performances of the proposed control method are evaluated using the on-sky measurement data recorded by the 1-m New Vacuum Solar Telescope (NVST) at Fuxian Solar Observatory (FSO). The results show that 95.85% of disturbances are effectively filtered by the hybrid control method. Compared with the full-OMGI, the narrow-band disturbances at different frequencies are significantly suppressed. And compared with the full-LQG, the execution time of identification procedure is reduced by 37.77% and the control calculation time is reduced by 73.8%, which is more beneficial for the real-time mitigation of disturbance.

In order to solve the problems of traditional atmospheric transmissometer, such as fixed transmitting-receiving baseline, limited sampling space, and poor applicability of transmittance model, a variable baseline atmospheric visibility measurement system is designed in this work. The laser emission unit of the system is fixed, while the optical receiving unit is movable, so the atmospheric transmittance can be obtained at different baseline lengths. By measuring the multi-point atmospheric transmittance and using the least square fitting, the atmospheric extinction coefficient and the atmospheric visibility can be obtained. Simulation experiments of the proposed system and the traditional transmissometer are carried out under the atmospheric visibility conditions of 200, 800, and 2000 m. The results show that the root mean square error of atmospheric extinction coefficient measured by the proposed system is less than that of the traditional transmissometer, which effectively reduces the influence of system error and random error on the measurement results. The effectiveness and reliability of the system are verified by the external field experiment in the atmosphere environment simulation chamber.

Contour targets are affected by turbulence clutters in near-ground remote imaging scenes, leading to large matching errors. To address this problem, we propose a shape point set matching recognition method based on an oriented shape context and an edge continuity constraint. In the proposed method, directional features are embedded into a traditional shape context to construct a feature operator with a scale and rotation invariance. Further, inspired by the priori of edge continuity between the template and target shapes, we add the edge continuity constraint condition of the contour shape into the target matching energy cost function to improve the accuracy of shape matching. The experimental results of shape matching in a synthetic turbulence clutter scene and a real remote imaging scene show that compared with the traditional method, the proposed method can reduce the target matching error by about 6% in clutter scenes and reduce computational complexity.

In a laser transmission system that uses an adaptive optical system, the polarization effect of optical thin films will cause the polarization chromatic aberration, decreasing the correction ability of the system. In this study, the polarization chromatic aberration analysis of the Cassegrain system is performed. First, we employ the Jones Matrix to describe the impact of the polarization aberration caused by optical thin films on the amplitude and phase. Then, the scalar wavefront is extracted from the Jones pupil using the singular value decomposition method, and is used to the wavefront detector and aberration analysis of a Hartmann wavefront detector. The wavefront fitting is performed using Zernike polynomials. Finally, we analyze the reduction of the correction ability of the adaptive optical system.

Airborne light laser detection and ranging (LiDAR) can obtain three-dimensional point cloud data with high accuracy, can reach the ground surface through forest leaves, and reflect the continuous terrain features of the study area quickly and accurately, which is conducive to the establishment of a high-resolution digital elevation model (DEM). In this paper, cloth simulation filtering (CSF) algorithm is applied to filter the airborne LiDAR data. By setting the number of particles generated in the algorithm and the threshold of ground point classification, the ground point cloud is extracted from six groups of point cloud data under different terrain conditions, and the Kappa coefficient of classification is between 0.851 and 0.954. The DEM of 1 m×1 m is generated from the ground points extracted by the CSF algorithm, and the DEM provided by the research area is linearly fitted. Experimental results show that the regression line fitting goodness factor R2 is larger than 0.99 and the root mean square error is between 0.10451 and 0.30387. The cloth simulation algorithm has few parameters for extracting ground points of the point cloud and is suitable for a wide range of terrain. The high-resolution DEM generated by the proposed algorithm can well express the continuous undulating surface changes and terrain features of the region.

Atmospheric refraction is one of the important factors affecting the optical measurement of the target's external trajectory parameters. Atmospheric refraction correction is necessary under the condition of higher measurement accuracy for optical equipment. aiming at the problem that the theoretical derivation process of standard method is not precise enough and repeated iterations are needed in the calculation process, based on atmospheric sphere sublayer and optical equipment features, an atmospheric refraction correction method based on angular intersection is proposed. Simulations and unmanned aerial vehicle flight test show that proposed method is faster and more accurate than the standard method.

In order to study the influence of ice crystal particles on the performance parameters of quantum interference radar, based on the Van de Hulst approximation theory of ice crystal particles, standard gamma distribution, and Henyey-Greenstein phase function, the polarization changes of radar detection photons in the background of ice crystal particles are studied. The influence model of different parameters of ice particles on transmission distance, resolution, and bit error rate of quantum interference radar detection photons is established. Simulation results show that increasing the effective scale of ice crystal particles will increase the energy dissipation of the detected photons, resulting in a decrease in the transmission distance of the detected photons. The resolution of the quantum interference radar decreases as the optical thickness of the ice crystal grains increases when the number of transmitted beam photons is fixed. Particularly, when the concentration of ice crystal particles is constant, the quantum bit error rate of the link increases with the increase of effective size of the ice crystal particles and the asymmetric factor. In addition, different types of ice crystal particles have different effects on the quantum bit error rate. Meanwhile, in the case of high polarization ratio, reducing the ellipticity angle within a certain range will accordingly bring down the quantum bit error rate.

The 241-element deformable mirror model is built using COMSOL Multiphysics, and the influence function data of the driver of the deformable mirror are acquired by calculation. Based on the sub-aperture slope method, a procedure is compiled, by which the optical aberration of the 241-element adaptive optics system is corrected. By taking the root mean square value of the residual fitting error of a 3-60 order Zernike polynomial, the optimal parameter is determined by analyzing the influence of the structural parameters of the deformable mirror on the correction capability. Under this optimal parameter, the coupling factor of the deformable mirror is calculated as 11%. The influence of the system on the fitting ability of the Zernike polynomial is analyzed considering that there exist different translation and rotation errors between the Hartmann sensor and the deformable mirror in the 241-element adaptive optics system. The results show that the translation and rotation errors are not greater than 3 mm and 6°, respectively.

As for the wave-front sensorless adaptive wave-front correction system based on the stochastic parallel gradient descent (SPGD) algorithm, its convergence speed is too slow to satisfy the real-time requirement of a wireless optical coherent communication system. The parallel processing base on the SPGD algorithm is introduced and the graphics processing unit (GPU) parallel computing is used to improve the convergence speed of the correction system. The average gray value of the surrounding 400 pixels centered on the centroid of the real-time spot detected by CCD camera is employed as the value of system performance index. GPU multithreading operation is used to accelerate the solving process of the performance index and the updating process of the deformable mirror control voltage vector. The results from the indoor experiments and the external coherent light experiments show that the Strehl ratio is larger than 0.8 and the maximum time acceleration ratio is up to 8.6. Moreover, the convergence speed of the GPU accelerated wave-front correction system is improved and simultaneously the correction effect is ensured.

The link transmission performance of the unmanned aerial vehicle (UAV) retro-modulating optical communication system under the weak turbulence condition is studied and verified by simulation. The influence of pointing error on the system is considered, and the Gauss-Hermite integral method is used to derive the bidirectional channel fading probability density function and the closed expression of its cumulative distribution function for this system. The closed expressions of system average bit error rate and the outage probability are further derived. The research results show that under the joint influences of weak turbulence and pointing error, and the incident angle, modulation order and refractive index of the corner cube retro-reflector have great influences on the error performance of this system. When the divergence angle is 3-10 μrad, the system error rate reaches an optimal value. When the divergence angles are 6, 8 and 10 μrad, respectively, the outage probability is reduced to 10 -9 orders of magnitude under the condition of relatively high signal-to-noise ratio threshold.

The cluster-cluster aggregation model of soot and the discrete dipole approximation method are used to analyze the single and multiple scattering channel characteristics of ultraviolet (UV) light under different soot concentrations and particles sizes as well as the influence of scattering angle on the scattering intensity. The research results show that with the UV line-of-sight communication method, the path loss increases with the increase of the soot concentration when the particle radius is the same, meanwhile when the soot concentration is constant, the path loss also increases with the increase of particle size. With the UV non-line-of-sight communication method, the larger the soot concentration and the original radius, the less the path loss of the scattering channels at a short distance. In contrast, at a long distance, the higher the soot concentration,the larger the path loss, however, the difference among path losses for different concentrations is small. In the case of multiple scattering, the scattering light intensity decreases with the increase of scattering angle, while when the scattering angles are the same, the higher the soot concentration, the greater the scattering UV light intensity.

By exploring the range errors from the target specular reflection, and analyzing the relationship between range errors and intensity data, a range error model from the target specular reflection based on original intensity data is established. Experimental results show that the original intensity data can be used to establish a range error correction model, which is independent of target material and surface geometry. According to the original intensity, the distance data can be accurately corrected, which is of great significance to improve the accuracy and quality of terrestrial laser scanning.

By using the sun photometer, nephelometer and particle matter monitor of national climatology observatory in Shouxian, the atmospheric optical characteristics in Shouxian are observed and analyzed in winter. The daily variation rules of optical depth of aerosol, scattering and absorption coefficient, and single scattering albedo are obtained. Results show that, with the increasing of aerosol content, particle matter content also increases, the optical depth of aerosol, scattering coefficient and single scattering albedo increase, and the aerosol's wavelength index and atmospheric turbidity coefficient also increase. The size changing of aerosol particles can be characterized by asymmetric factors, backscattering ratio, scattering coefficient, single scattering albedo and wavelength index together.

The single-light-source dual-optical path visibility meter is a kind of camera type visibility meters, and its light source and optical path system directly affect the accuracy of visibility inversion. In view of the error caused by the instability of the light source and the split light path in the original system, the integrating sphere is used as the improved source of the single-light-source dual-optical path visibility meter, and the near and far reflection end is used to split an integrating sphere light source. The near and far light spots captured by the camera are extracted and brought into Koschmieder's law. The experimental results show that compared with the LED light source, the integrating sphere light source proposed in this paper reduces the uniformity error by 5%. Compared with the transmission type visibility meter LT-31 and the scattering type visibility meter VPF-730 under different visibility conditions, the root-mean-square (RMS) relative error and relative average error of this scheme are much less than 20%, which is in line with the WMO's error requirement of the visibility meters.

This study presents a stochastic parallel gradient descent (SPGD) algorithm based on the optimization of square of wavefront aberration gradient to improve the convergence speed of the SPGD algorithm for correcting the wavefront aberrations. Based on the principle of the SPGD algorithm, this study analyzes the constrained factors of the convergence speed in the algorithm iteration. Further, the linear relation between the square of wavefront aberration gradient and disturbances from random aberration is analyzed by deriving the theoretical formula; subsequently, the square of wavefront aberration gradient is approximately calculated by using the far-field spot's normalized second moment, and the optical correction of wavefront aberrations is finally realized. The convergence speed and correction effect of the proposed SPGD algorithm are then analyzed using numeric simulations and compared with those of the previous SPGD algorithms. Finally, a wavefront sensorless adaptive optics correction experiment for Fresnel zone plate wavefront aberrations is performed to validate the performance of the proposed SPGD algorithm. The numeric simulation and results of correction experiments consistently denote that the proposed method has a high convergence speed and a robust corresponding adaptability.

During the inversion of atmospheric extinction coefficient, choosing the boundary value of the extinction coefficient is critical. In this study, a new method based on lateral Steffensen-like third-order method is proposed for determining the boundary value of atmospheric aerosol extinction coefficient. To confirm the method reliability, the proposed method is applied to both simulated and actual measured echo signals. Results show that the proposed method has high iterative speed and converges to the boundary value of extinction coefficient after a few iterations, which can invert atmospheric extinction coefficient more accurately.

The extinction coefficient, depolarization ratio, and haze height of atmospheric aerosols during hazy weather are used to realize real-time atmospheric monitoring and study the optical characteristics of aerosols in hazy weather conditions. These characteristics are retrieved based on the observation data obtained from a multi-wavelength aerosol lidar at the Haidian Meteorological Bureau in Beijing, China, from November 4 to 7, 2017. Combining these characteristics with the meteorological parameters obtained from the sounding data, the air mass source and direction during hazy weather conditions are analyzed using the hybrid single particle Lagrangian integrated trajectory (HYSPLIT) model. The analysis concludes that increased relative humidity, low wind speeds, and the presence of an inversion layer are important factors for the formation of hazy weather conditions. The transportation of pollutants through the Hebei Province influences the formation of the haze in Beijing's Haidian District, and haze dissipation is affected by the northwest wind, which provides main conditions for the upward diffusion and disappearance of pollutants.

An atmospheric delay correction model based on a ray-tracing algorithm and a surface pressure model are proposed in this paper. As atmospheric parameters for the models, atmospheric data from the National Centers for Environmental Prediction (NCEP) are introduced in the models for the numerical simulations of atmospheric delay corrections of satellite-borne laser altimeters. The result shows that the atmospheric correction along the zenith direction is approximately 2.30 m. By applying sensitivity factors, such as the temperature, precipitable water, station height, and altitude angle, to analyze the sensitivity of the atmospheric delay correction, it is found that the atmospheric delay effect has a low sensitivity to the temperature and precipitable water, while has a strong sensitivity to the satellite altitude angle and station height. The results of this work can be used as a reference for determining the operable conditions for subsequent satellite-borne laser ranging research.

An adaptive bit loading algorithm is proposed based on visible-light pixelated multiple-input and multiple-output (MIMO) systems to deal with the problem of high number of bit errors for some subcarriers caused by the high-frequency attenuation, which is attributed to the absorption and scattering of channels and lens blur in underwater visible-light pixelated MIMO systems. By ensuring that the total number of bits allocated across all the subcarriers remains constant, the proposed algorithm dynamically selects the optimal subcarrier modulation order according to the signal-to-noise ratios of the subcarriers to reduce the number of bit errors for each subcarrier and improve the system reliability. The simulation results denote that the bit error rate can be considerably reduced when the transmission rate of the pixelated MIMO system is maintained constant.

An automatic spot location and extraction algorithm based on the combination of the Otsu method and the centroid method is proposed herein for the grating wavefront curvature sensor and verified through experiments. The original intensity distribution image is first binarized by using Otsu method. Then, the binary image is then segmented into two binary images according to the centroid coordinates such that each binary image contains one spot. Finally, the centroid coordinates of the two images are calculated as two spot centers in the original intensity image, while the two spots in the original image are extracted from the original intensity image. An experimental setup of the grating wavefront curvature sensor is built based on an off-axis Fresnel zone plate to verify the effectiveness of the proposed algorithm. In the experiment, the spots are extracted automatically by using the above algorithm; then, the wavefront is restored by using Laplacian eigenfunctions. The results are compared with those of the Hartmann wavefront sensor. The experimental results demonstrate that the proposed algorithm can extract spots automatically with an error less than 4 pixel.

The performance of a multi-aperture coherent optical receiver based on the equal gain combining algorithm is analyzed for the satellite-to-ground downlink. Atmospheric turbulence, weather conditions, and aperture averaging effect are considered. The analytical model of bit error rate is deduced. Then the effects of the atmospheric turbulence, weather conditions, and aperture size on the sensitivity of the receiver are analyzed, which provides effective guidance for practical applications.

In order to enhance the perception for the multi-scale image variation and improve the scale invariance of convolutional neural networks,this study proposes a typhoon classification model based on multi-scale convolutional feature fusion. A multi-scale perception layer is added to convolutional neural networks; then, convolutional features are multi-scale perceived and cascaded. A multi-scale regularization term is then incorporated into the loss function. The residual error of hidden layer weight is minimized and the feature extraction ability is optimized with backpropagation. Finally, multi-scale high-level semantic features are normalized to the probability value of each category using Softmax. The maximum probability value is used as the final classification result of the image. Infrared satellite cloud images are used as the dataset in our experiments to validate the multi-scale perception ability of the model. Experimental results show that the model can effectively perceive and extract the local features of the typhoon cloud map. The generalization ability of the model is verified using two general datasets, i.e., MNIST and CIFAR-10.

In this study, the intensity and phase distributions of a ring Airy-Gaussian vortex beam propagating in atmospheric turbulence are numerically studied based on the split-step Fourier method. The propagation characteristics of the ring Airy-Gaussian vortex beam in atmospheric turbulence are discussed and compared to those in a free space. The impacts of propagation distance and distribution factor on the average intensity of ring Airy-Gaussian vortex beam in atmospheric turbulence are revealed. Results demonstrate that the phase wavefronts of the beam during the propagation process are distorted due to the random disturbance of the atmospheric refractive index. The equiphase line of the beam turns into an arc due to the orbital angular momentum, and the arc becomes non-smooth gradually with the increase of the propagation distance. In addition, the variation of the average intensity of ring Airy-Gaussian vortex beam with the propagation distance in atmospheric turbulence follows the Airy function distribution. The smaller the distribution factor is, the more obvious the variation of the phase wavefronts with the propagation distance is. The stability and propagation quality of the beam are affected by the distribution factor.

Based on lidar observational data of atmospheric particulate matter, ground monitoring station data, and wind field data measured by an ultrasonic anemometer on a tower (later referred to as tower wind field data), a pollution process that occurred from January 16 to 18, 2018 in the northern Zhejiang Province and its characteristics were comprehensively analyzed. The results show that the pollution process is primarily caused by regional pollutant transport. The lidar results show that pollutants in northwest cities begin to be transported to Ningbo via a northwest wind at 12:00 on January 16, causing the concentration of particulate matter to increase rapidly. The wind direction switches to a weaker southern wind at 18:00 on January 17, resulting in the dissipation of the pollutants. The 532 nm range-square-corrected signal is in agreement with the variation trend of the near-ground pollutant concentration; the depolarization ratio and wavelength dependence show that the pollutants at a height of 0.5-1 km and those near the ground are of two different types. The results of the HYSPLIT backward trajectory model show that the polluted air mass comes from the northwest city of Ningbo and is transported at a high speed, consistent with results analyzed from the tower wind field data. Therefore, the lidar observational results can effectively characterize the spatial distribution and evolution of the particulate matter concentration and provide a theoretical basis for air pollution monitoring and early warning systems.

The technology of computationally adaptive plenoptic imaging system (CAPIS) can simultaneously record the position and direction of a signal, obtain the distorted wavefront slope from the light field information, and thus perform the wavefront reconstruction. This study investigates the optical wavefront distortion detected by the CAPIS technology, and provides a numerical calculation model for simulation analysis. The results denote that the CAPIS technology can accurately detect a low-order aberration wavefront. Furthermore, the root mean square value of the wavefront residual is less than 0.1λ. The experimental light path is established, and the detection of the low-order aberration wavefront is realized and the root mean square value of the wavefront residual is less than 0.5λ. The simulation and experimental results denote that the CAPIS technology can effectively detect a low-order aberration wavefront, which is considerably significant for exploring one large-field wavefront detection method.

Herein, the effect of laser pulse time delay induced by seawater scattering is studied using the Monte Carlo numerical simulation method. Further, we analyze the effects of seawater types, transmission distance, and transceiver parameters on laser pulse time delay. The numerical simulation results indicate that in clear seas, the laser pulse time delay broadening does not obviously change with the increase of transmission distance. Furthermore, when the transmission distance is less than 50 m, the channel time delay is smaller than 0.5 ns, indicating the transceiver parameters exhibit only small impact on the channel delay. However, in turbid seas, the receiving power and the channel time delay increase with the increase of receiving aperture under the multipath effect induced by channel scattering. When the receiving angular field of view (AFOV) is less than 90°, its influence on the receiving power and the time delay broadening is observed to be significant. However, when the AFOV is between 90° and 180°, the receiving power and the time delay broadening demonstrate no obvious changes with AFOV.

On the basis of our study of 55 samples collected during four cruises in the Yellow and Bohai Seas off the east coast of China (November 2014, August 2015, July 2016, and January 2017), we developed an algorithm for estimating the sea-surface density (SSD) using remote-sensing reflectance. Our results show that the multivariate linear regression model performs the best, with a determination coefficient of 0.70 and a mean absolute percentage error of SMAPE=3.49%. We used an independent dataset (27 in situ observations) to assess the performance of the model, yielding a validation result of SMAPE=3.27%. In addition, the sensitivity experiment of the model show that the observed fluctuation in the SMAPE values is <3%, indicating that our proposed model is relatively stable. Meanwhile, we applied our developed model to the geostationary ocean color imager (GOCI) satellite data recorded in July 2016 and successfully produced the SSD distribution pattern. The spatial characteristics show that the coastal waters, the central parts of the Bohai and Yellow Seas, and the waters off the northern Shandong Peninsula have relatively high SSD values, while relatively low values are distributed along the Qingdao coast.

To study the regions of spreading of truncated beams propagating through non-Kolmogorov turbulence, the expressions for turbulence distance and Rayleigh range are derived, the transport path is divided into three regions, and the relevant numerical analysis of the three regions is given. Results show that the lengths of the first region and the second region decreases with increase of coherence and truncation parameter, and the starting point of the third region reduces with increase of coherence and truncation parameter. The smaller coherence and truncation parameter are, the more likely it is to ignore the effect of turbulence on the beam propagation in Rayleigh range. In the three regions, the turbulent distance increases with the change of the generalized exponential. The corresponding physical explanations are given for the main results.

With the increasing usage frequency of airborne photoelectric radar, its detection distance seriously deviates from the factory indicators. Thus, the working principle of airborne photoelectric radar and the influences of the radiation intensity of the target, atmospheric condition and optical system on the maximum detection distance are analyzed. According to the detection principle of photoelectric radar, the design idea of a new type of portable test system is put forward. The blackbody and parallel light pipes are used to simulate the infrared radiation intensity of targets at infinity and the attenuation feet, stepping motor and transmission gear are combined to simulate different atmospheric conditions. Thus its prototype is ultimately determined and the infrared attenuation measurement test is finished. In addition, the application method and test results of the novel portable photoelectric radar test system are described. As for this test system, it is easy to carry, its test efficiency is high, it is suitable for extremely harsh environmental conditions, and it can be extended to various types of infrared detection system performance tests.

Terahertz wave at frequency range from 0.1 THz to 10 THz has advantages such as large transmission capacity, good direction, high transmission efficiency and so on. Studying the application to the communication field plays a very important role in satisfying the demand of higher transmission rate for users. The terahertz time-domain spectroscopy (THz-TDS) system is used to measure the terahertz wave transmission data from 0.1 THz to 2.4 THz in atmosphere with different humidities for a 0.6 meters transmission distance. And based on the classical model of extracting optical constants proposed by Dorney et. al., the data such as delay time, power spectrum, amplitude spectrum and absorption coefficient are obtained. The results show that the water vapor in the atmosphere has obvious absorption and attenuation effects on terahertz, and the attenuation rises with the increase of humidity, especially in absorption peak. At the same time, there is transparent window of weak attenuation which can be applied to terahertz communication.

In order to obtain the optical concealment depth of underwater submersible by satellite remote sensing data inversion and realize large scale measurement in time and space, we propose an optical concealment depth remote sensing inversion method based on the quasi analytical algorithm (QAA). At the same time, it is a new way for underwater vehicle equipped with the optical concealment depth measuring device. According to the optical depth concealment model, Aqua-MODIS and Terra-MODIS satellite remote sensing reflectance data is used on the grid. After preprocessing the data, the remote sensing reflectance cross calibration data quality control is completed, and the Terra and Aqua satellite data is cross-corrected. According to quasi analytical algorithm and Doron algorithm, the optical concealment depth remote sensing inversion model is established. The optical depth concealment fusion product for specific sea area is made. Three bands remote sensing reflectance data of 443 nm, 488 nm, and 555 nm is inputted for the model. The data level is L3m, and spatial resolution is 4 km. The longitude range of data is from 100°E to 125°E, and the latitude range is from 10°N to 38°N. The results show that, based on quasi analytical algorithm, optical concealment depth remote sensing inversion technology is a feasible path. A new method to obtain optical depth concealment is developed. The method provides a calibration method for underwater vehicle equipped with the optical concealment depth measuring device, and it also provides important technical support for underwater optical depth detection and anti-detection and other military applications.

In order to study the aerosol multiple scattering effect on the transmission characteristics of polarized light in the region, we retrieve the microphysical optical parameters of the aerosol, including optical thickness, complex refractive index, particle spectrum distribution, through the inversion of the measured data from the CE318 solar spectrometer. The influence of the complex refractive index of particles, the effective radius of particle swarm and the polarization state of incident light on the transmission characteristics is analyzed through the Monte Carlo vector radiative transfer model. The results show that the transmission characteristics of the smaller particles are more sensitive to the real part change of the complex refractive index. In addition, with the increase of the imaginary part of the complex refractive index, as an important factor affecting the characteristics of radiation transmission, the absorption is stronger and the transmission characteristics is worse. If the effective radius of the particle group is larger, the transmittance of the light wave will be lower and the reflection rate will be higher. The polarization state of the incident light has little influence on the transmission characteristics. Compare to the other types of polarized light, the transmission and reflection rate of horizontally polarized light are greatly affected by the incident angle.

Based on the comprehensive observation data observed in the Beijing southern suburbs observatory, such as aerosol extinction coefficient and particle depolarization ratio obtained from aerosol lidar detection, wind field obtained from Doppler wind lidar, PM10 and ground meteorological elements, we analyse strong sand and dust weather process on May 4-5, 2017. The results show that on the afternoon of May 3, the horizontal wind speed begins to decrease, and the vertical downward airflow appears in the upper air, which are conducive to the dust falling from high altitude to the ground. During 12:00 to 20:00 of May 4, the vertical air flow occurs in the entire height layer from 40 m to 1350 m, and the maximum speed reaches 2 m/s, leading to the spread of low-level dust to high altitude. The three-dimensional distribution of dust is obtained from the lidar product: the initial dust layer height is about 1 km, the mid-term dust height is about 2 km, and the later dust height gets over to be about 1 km. The related coefficient of variation between the extinction coefficient of the lowest observation height of lidar and the variation of ground PM10 concentration is 0.8308. The study shows that the combination of aerosol lidar and wind-measuring lidar can effectively monitor and predict the distribution and diffusion of atmospheric aerosol.

A fast atmospheric correction method is used to eliminate the effects of the atmosphere on electromagnetic wave transmission. Aerosol retrieval and atmospheric correction look-up tables are constructed based on the atmospheric radiation transmission model. Aerosol optical depth (AOD) is derived by the dark target algorithm. The atmospheric correction parameters are calculated by the pixels. Using the visible infrared imaging radiometer suite (VIIRS) data on a new polar-orbiting operational environmental satellite, we analyze the difference of vegetation reflectance and water reflectance, and the change of normalized difference vegetation index before and after atmospheric correction. In addition, the results of the fast atmospheric correction are also verified by the measured spectral data and moderate resolution imaging spectroradiometer （MODIS）surface albedo data. The verified results show that the spectral curve of ground object after the atmospheric correction is closer to the measured spectral curve. Compared with MODIS surface reflectance products, the fast atmospheric correction is of high accuracy, and the error is less than ±0.04, so it has more quantitative applications of remote sensing data.

Accuracy of the upward longwave radiation data of GEWEX-SRB (Global Energy and Water Exchanges Project-Surface Radiation Budget), ISCCP-FD (International Satellite Cloud Climatology Project-Flux Data) and CERES-SYN (Clouds and the Earth′s Radiant Energy System-Synoptic Radiative Fluxes and Clouds) in polar regions is studied. In the experiment, two kinds of ground observation data of BSRN (Baseline Surface Radiation Network) and CEOP (Coordinated Energy and Water Cycle Observations Project) in polar regions are used as reference data, and the downscaling method is used to deal with them. Finally, accuracy of the radiation products is evaluated. Research results show that the overall accuracies of the three kinds of commonly used upward longwave radiation data are lower in polar regions. Absolute values of the root mean square error (RMSE) and the mean absolute error (MAE) are more than 15 W·m-2. The mean RMSEs of GEWEX-SRB, ISCCP-FD and CERES-SYN are 23.70 W·m-2 (8.69%), 25.14 W·m-2 (9.62%) and 22.98 W·m-2 (8.80%), respectively, and the mean MAEs are 18.53 W·m2 (6.96%), 20.09 W·m2 (7.70%), and 17.73 W·m2 (6.79%), respectively. Through the analysis of accuracy, the factors that affect the accuracy of the upward longwave radiation products include spatial heterogeneity, input parameter errors, cloud influence and low spatial resolution of radiation products and so on.

A vortex beam can effectively improve the channel capacity of the communication system, however in the atmospheric environment, the optical communication channel is influenced obviously by the atmospheric turbulence. Thus it is of great significance to study the transmission characteristics of a vortex beam in the atmospheric turbulence. The Kolmogorov spectral model is widely used to describe the atmospheric turbulence previously, but the further researches show that the atmospheric turbulence also has the non-Kolmogorov spectral characteristics. Therefore, the investigation of the non-Kolmogorov spectral transmission characteristics for a vortex beam is conducted. Based on the numerical methods, the influence of outer- and inner-scale of turbulence, generalized exponential factor, refractive-index structure constant on the spiral spectral distributions, topological detection probabilities and others of a Laguerre-Gaussian beam after different transmission distances is investigated. The simulation results show that the topological detection probability is closely related with the above parameters. Finally, a numerical method for calculating the scintillation index is proposed, and the influence of turbulence on bit-error-rate (BER) is figured out. The results show that when the beam is propagated up to 1000 m even in a weak turbulence, the BER is still difficult to meet the communication requirements, and thus a further phase correction is quite necessary.

In order to explore the extinction characteristics of different types of aerosols and effect of multiple scattering on the transmission performance of visible light, four wavelengths of 400, 488, 550, 694 nm and four common aerosols of oceanic, dust-like, water-soluble and soot are selected. Based on the Mie scattering theory and the steady-state Monte Carlo model, the transmission attenuation characteristics of visible light in atmosphere are studied. The results show that the scattering intensity of single particle decreases with the increase of incident wavelength. The extinction efficiency factors of oceanic, water-soluble and soot particles decrease with the increase of wavelength, whereas dust-like particles have opposite effect. The extinction characteristics of oceanic, dust-like and water-soluble particles are dominated by scattering, while soot particles are dominated by absorption. The results of simulation of multiple scattering by steady-state Monte Carlo method show that the transmission rates of light wave in oceanic aerosols, dust-like aerosols, water-soluble aerosols and soot aerosols decrease in turn. The transmission rate increases gradually with the increase of visibility. The absorption effect can be neglected in multiple scattering processes when the visibility reaches a certain degree. This conclusion is helpful to construct a more accurate image degradation model in a imaging path of specific aerosol optical thick.

The tropospheric aerosols in the northern suburb of Nanjing is observed and analyzed with the Rayleigh-Raman-Mie lidar in Nanjing comprehensive observation base of the China Meteorological Administration. The Raman scattering signals with the wavelength of 607 nm are smoothed by the wavelet denoising method on the basis of soft threshold filtering. The extinction coefficient of upper tropospheric aerosols is retrieved based on the data from Raman channel of the lidar. The backscattering coefficient and the lidar ratio of upper tropospheric aerosols are retrieved with the Mie scattering signal with the wavelength of 532 nm. The experimental results show that the wavelet denoising method on the basis of soft threshold filtering can remove the signal noise well and improve the accuracy of the retrieval results. In sunny and cloud-free day, the extinction coefficient of upper tropospheric aerosols is from 0.03 km-1 to 0.07 km-1, the aerosol backscattering coefficient is from 0.011 km-1·sr-1 to 0.024 km-1·sr-1, and the lidar ratio is from 22 sr to 52 sr. It is indicated that there are still some aerosol particles in upper tropospheric of the northern suburb of Nanjing. Cirrus clouds have been measured many times during the experiment. The lidar ratio cirrus clouds is 17 sr±10 sr.

Based on the ranging principle of satellite laser ranging (SLR) system, the distribution of echo photon reflected back from the angle reflector is simulated numerically, and the relationship between the shape effect of the satellite angle reflector and the ranging precision of SLR system is analyzed and discussed. In addition, in order to verify the applicability of the shape effect of the satellite angle reflector, the satellites at different orbits are observed by the SLR system in Changchun Observatory, National Astronomical Observatories, Chinese Academy of Sciences. The results show that the shape effect of the satellite angle reflector has significantly changed the distribution of the echo photons reflected from the satellites, and the laser pulse width is broadened. For Starlette, the laser pulse width is extended from 50 ps to 72 ps, and the ranging error caused by the shape effect of the satellite angle reflector is about 5.4 mm. For the high-orbit Etalon-1 satellite, the middle-orbit Lageos-1 satellite and the low-orbit LARES satellite, the ranging errors are about 15.4, 7.4, 5.0 mm, respectively. Therefore, for the development of the measurement accuracy of SLR system to the mm level, the influence of the shape effect of the satellite angle reflector on the ranging precision should be considered, which also provides new ideas and approaches for the evaluation performance and structure design of SLR system.

One-dimensional lidar signal is achieved by the simulation combining an atmospheric model and the design of parameters of imaging lidar. A two-dimensional light cross image is recovered based on measured beam widths and features of the Gauss distribution. The noised images similar to the real signals detected by imaging lidar are obtained when we add Gauss white noise with different intensities and certain intensity of average background to the original image. The good de-noising effect is obtained when we denoise the noised lidar light cross image by the two-dimensional wavelet transform method. The relative error between echo signal after denoising and original echo signal is in the range of ±12%. The extinction coefficients of aerosol are retrieved with de-noising lidar signals. Comparing extinction coefficients under the input aerosol atmospheric model with retrieved extinction coefficients of aerosol, we find that the relative error is in the range of ±15% and their variation trends are coincident, which verifies the feasibility of the proposed method using wavelet transform in the de-noising for the noised images of lidar.

The observation of solar activity has problems of small field of view and low resolution. The field of view corrected by a single-conjugated adaptive optics system is small, and a multi-conjugated adaptive optics system based on the method of three-dimensional reconstruction is time-consuming and complex. However, a solar ground-layer adaptive optics system, which corrects ground-layer turbulence, can achieve high efficiency and large field of view, and obtain high-resolution images. In the case of the distribution of four star array and with the average algorithm, the YAO software is used to the numerical simulation of the solar ground-layer adaptive optical system with 40″ and 60″ optimized field of view in J and H bands, and the simulation results are compared with that of single-conjugated adaptive optics system simulation under the same conditions. The results show that Strehl ratio of the ground-layer adaptive optics system increases 130%-210% compared with that of single-conjugated adaptive optics system within imaging field of view of 60″-120″, which is consistent with the results obtained by other softwares in solar adaptive optics.

Background noise from SO2, NO2 and other interfering gases in flue gas is corrected by the transverse Zeeman effect. The mercury concentration in flue gas is determined by Zeeman atomic absorption spectrometry. The average concentrations of element Hg (Hg0) in flue gas before and after wet flue gas desulfurization (WFGD) are 0.36 μg·m-3 and 11.08 μg·m-3. The concentration of Hg0 in flue gas increases significantly after desulfurization system. The monitoring results show that about 99% of SO2 in the flue gas is absorbed by the desulfurization slurry, and produces enough sulphite which reacts chemically with Hg2+ to release Hg0. The change of pH value in the desulfurization slurry also accelerates reduction reaction and release of Hg0. The use of WFGD system to remove mercury can lead to the increase of element mercury concentration. The monitoring results of element mercury have certain correlations with concentrations of other components in the flue gas, which is consistent with the theoretical analysis. The monitoring results show that transverse Zeeman atomic absorption spectrometry can effectively overcome interference caused by SO2, NOx and other gases. The results confirm the accuracy and feasibility of transverse Zeeman atomic absorption spectrometry applied in the detection of mercury content in flue gas.

Atmospheric temperature profile is an important parameter for climate, meteorology and atmospheric radiative transfer calculation. Temperature profile data of products inversed from data measured by moderate resolution imaging spectroradiometer (MODIS) exists on scanning strip per 500 m×500 m with the vertical resolution of 1 km. Based on the optimal interpolation method, the monthly averaging data of ground sounding site is used to correct the MODIS-inversed atmospheric profiles. In the area with ground sounding sites, the corrected results are compared with the profiles obtained by real-time ground sounding detection of a day, and it is shown that the average error and the root mean square error decrease more than 10%. In the area without ground sounding sites, we use the weighted average data of several sites around the target area to correct the MODIS data, and compare the correction results with real-time balloons data of the day. We find that the average error and the root mean square error greatly decrease.

Based on the non-Kolmogorov turbulence spectrum and the theory of second moments, a general analytical expression of beam wander model in non-Kolmogorov turbulence is derived. The results indicate that the beam wander depends on turbulence parameters including the generalized exponent parameter α, refractive index structure parameter C2n, turbulence outer scale L0, turbulence inner scale l0 and initial second moments of laser beam at the input plane. Taking the partially coherent anomalous elliptical hollow Gaussion beam (PCAEHGB) as an example, we simulate the root-mean-square (RMS) beam wander Bw and the relative beam wander Br numerically. It shows that Bw and Br increase with the increasing generalized exponent parameter, refractive index structure parameter, turbulence inner scale, turbulence outer scale, coherence length and beam waist radius. The results also indicate that Bw≈0.22 m when C2n=10-14 m3-α and the total propagation path length L=10 km, and Br reaches the maximum value when L≈5 km. Furthermore, PCAEHGB is less affected by turbulence than Gaussian-Schell model beam under the condition of the same parameters.

The source apportionment of carbonaceous aerosol in Hangzhou is carried out with aethalometer model, and the study is based on different light absorption properties of aerosols from different origins. Combined with aerosol time-of-flight mass spectrometer and data measured by aethalometer, the parameters of aethalometer model are corrected. The aethalometer data from Zhaohui environmental monitoring site of Hangzhou in 2015 is analyzed, and the contribution rates of biomass and fossil fuel burning to carbonaceous aerosol in Zhaohui are analyzed. The results show that the annual concentration of carbonaceous aerosol originating from fossil fuel in 2015 is 15.4 μg/m3, and the annual concentration rate is 71.8%. The monthly contribution rate of biomass burning to carbonaceous aerosol is 20%-38%. The minimum concentration rate appears in July while the maximum concentration rate appears in December, and the monthly data shows a gradient transformation. Traffic rush hours exhibit no effect on the mean diurnal pattern of absorption exponent, which means the carbonaceous aerosol may be introduced by long-range transport. The above results build the foundation for identification of Hangzhou energy consumption structure and alleviating air pollution.

Based on the introduction of the characteristics of Fengyun-3 E star (FY3E) day/night orbit meteorological satellite and low-light imager and according to FY3E orbit parameters, the Satellite Tool Kit (STK) simulation technology is used to simulate and analyze the external stray light, which comes from the sun and the moon and enters into the remote sensor (low-light imager) loaded in FY3E. The method of light shield is proposed to suppress the stray light. The results indicate that the stray light has the greatest impact on the remote sensor on 2016-12-18 when the angle between the sun vector and the normal vector of remote sensor bottom window is minimal. The effect of stray light caused by the moon on remote sensor is further analyzed, and it can be avoided when the sun shade condition is satisfied. Therefore, when we design the shade, the angle between the sun vector and the normal vector of remote sensor bottom window is only needed to consider. At present, the field-of-view of the remote sensor is 55°, and the efficiency of shading stray light is low. To improve the shading efficiency of stray light and not affact application, the field-of-view of the remote sensor should be reduced to 50° and the size of the light shield should be decreased.

The optical property of atmospheric aerosol in Nangjing is inversed, and the different factors which can influence the inversion accuracy of extinction coefficient of atmospheric aerosol are studied. The de-noising processing for signal is carried out by different methods，and the suitable de-noising method is found. The reprocessing for de-noised signal is carried out with five-point triple smoothing, wavelet de-noising and eleven-point smoothing respectively, and the method which can obtain accurate inversion result is chosen. The effects of logarithmic ratio of backscatter extinction and extinction coefficient at the reference height on the inversion result of Klett method are analyzed. The inversion results when k ranges from 0.67 to 1.0 and σm is about 1×10-5 km-1 are analyzed. The influence of the lidar ratio on the inversion result of Fernald method is analyzed when the lidar ratio ranges from 20 to 70. The results of Klett method are compared with that of Fernald method. It is found that in the region with low atmospheric aerosol content, the results of the two methods are different, but the results of the two methods are almost same in the region with high aerosol content.

Fuzzy control is used in wavefront correction and its feasibility has been confirmed because it does not depend on the response model of deformable mirror. The wavefront correction effect of fuzzy proportion integration differentiation (PID) control in adaptive optical system is assessed, including testing fuzzy correction bandwidth, selecting fuzzy input and output domains, and optimizing fuzzy rule base and wavefront weighted template. Experimental results show that the selection of fuzzy domain is reasonable, and the better results are obtained with a 3×3 wavefront weighted template. When the initial values of KP、KI and KD of PID controller are 0, the rule base with membership degree positive distribution is more suitable for the fuzzy output domain. When the refresh rate of the Hartmann-Shack sensor is 120 Hz, the system correction bandwidth is 5-6 Hz, which is consistent with the conventional PID.

Both the mathematical principle of the maximum probability (MP) method and the process of iterative equations are introduced. Then we use the real satellite data as an example to demonstrate the calculation of MP method and obtain the volume scattering ratio profiles and scattering coefficient profiles of polar mesospheric clouds (PMCs). We compare the inversion results of the MP method with those of the traditional onion peeling (OP) method, and find that the former hardly have any distortion, while the latter show serious distortion. The fundamental reason for this difference is that the OP method assumes that the volume scattering intensity has a uniform distribution in the same atmospheric layer, while the MP method assumes that the volume scattering intensity can exhibit a non-uniform distribution within a certain varied range of the layer. This assumption of MP method is more suitable for the natural characteristics of PMCs, because the spatial distribution of PMCs often changes greatly in a short time.

A light intensity expression of the partially coherent beam with spherical aberration propagating in the oceanic turbulence is obtained by the extended Huygens-Fresnel diffraction integral formula. Light intensity characteristics of the partially coherent beams with spherical aberration propagating in the seawater are investigated by means of numerical calculation. Results show that the larger the mean square temperature dissipation rate χT is, the smaller the dissipation rate of turbulence kinetic energy of unit mass liquid ε is, or the larger the relative intensity of temperature and salinity fluctuations w is, the more obvious the effect of oceanic turbulence on the expansion of the beam is. The smaller the χT is, the larger the ε is, or the smaller the w is, the smaller impact of oceanic turbulence on the beam expansion is. At the same time, the smaller the coherence length of the beam is, or the greater the spherical aberration is, the more the beam spread is. However, the influences of the spherical aberration parameters on the diffusion of the laser are significantly weaker than that of the oceanic parameters when the beam propagates in the seawater.

The molecules and aerosols in atmosphere have a strong scattering effect on ultraviolet light, so the ultraviolet light can propagate in atmosphere in the condition of non-line-of-sight. In the ultraviolet detection, the transmitter is close to the receiver. In order to study the propagation characteristics of ultraviolet light, a multiple-scattering model is established based on the Monte Carlo method, and the model is optimized by the point probability method. The pulse response and the energy density received by the detector in different atmosphere conditions are analyzed through simulation when the axes of transmitter and receiver are coplanar and non-coplanar. The simulation results show that the ultraviolet laser detection is different from remote target detection, and the deflection angle has a great influence on proximate target detection. When the scattering coefficient and absorption coefficient are large and the distance between the transmitter and the receiver is short, the echo signal is strong. The simulation results are helpful to understand the propagation characteristics of ultraviolet light in the atmosphere, and provide the theoretical foundation for the design of ultraviolet laser detection in the future.

Transferring of quantization noise in algorithm implementation is tracked, which is caused by the finite sampling width of far field photodetector. The effect of quantization noise on wavefront aberration correction effect and convergence speed is analyzed. According to the changing of Strehl ratio (SR), a modal reconstruction algorithm based on dynamic region extraction is presented. Numerical calculations are carried out with the wavefront which fits the Kolmogrove atmospheric turbulence power spectrum and is obtained by the simulation of 18- and 33-order Zernike terms. The results show that, under the condition of the camera sampling width of 12 bits and 33-order initial aberration, the SR is larger than 0.9, the root-mean-square value of wavefront recuperative residual is 0.058λ (λ is wavelength), and the algorithm is converged after iteration for 31 times. The proposed algorithm greatly improves the correction performance and convergence speed of the wavefront sensorless adaptive optics system and reduces the effect of the quantization noise.

In order to monitor the working status of marine ecological monitoring instruments, a three-gear zoom optical system with large relative aperture is designed. This system is designed with Zemax software and its total length is 200 mm. The system uses a 6.4 mm×4.8 mm CCD camera, and the three-gear zoom focal lengths are 8, 14, and 28 mm, respectively. The relative aperture remains at 1/1.4 during zoom process. The maximum field of view is 52° with short focus. At maximum field angle, when the Nyquist frequency is 42 lp/mm, the modulation transfer function (MTF) of the system at 0 field of view is 0.8, the average MTF is 0.7 at 0.707 field of view, and the average MTF value at 1 field of view reaches 0.6. In 10 μm range, the diffraction encircled energy is 90%, and distortion control is in a reasonable range. The system has high zoom ratio, simple structure and large relative aperture. It is suitable for monitoring the marine ecological monitoring instruments and can timely feedback their working status information. Therefore it greatly reduces the maintenance cost of marine ecological monitoring equipment.

The action range of airborne infrared search and track (IRST) system is affected by the large humidity of atmosphere in low latitude areas. Aiming at this problem, the main factors affecting the atmospheric transmittance are analyzed based on the atmospheric data in low latitude areas in recent years. The mathematical model of atmospheric transmittance is established. The impact of height and oblique distance are also revised. Atmosphere transmittance at the wave band from 3 μm to 5 μm is analyzed by using Matlab under different seasons, weather conditions, pitching angles, heights and distances. Comparing with the simulation results of LOWTRAN7, the error is about 5%, which verifies the effectiveness of the model. The conclusion has significant reference value on guiding the practical operation of IRST system.

The atmospheric boundary layer height has important influence on particulate air pollution. A statistical investigation of atmospheric boundary layer height based on a large amount of Lidar data from multiple sites is used to analysis the characteristic in the Jing-Jin-Ji area. The atmospheric boundary layer height retrieved from the Lidar data is compared with the national weather service national centers for environmental prediction global data assimilation system forecast model result. Statistical results show that the atmospheric boundary layer of the Jing-Jin-Ji area has obvious characteristics of diurnal and seasonal variations, and the atmospheric boundary layer height is higher in the daytime than at night, and the peak value of the atmospheric boundary layer height occurs at 14:00. The atmospheric boundary layer height during the summer and autumn is higher than spring and winter, the atmospheric boundary layer height in winter also has a decreasing tendency. In addition, the statistical result of November 2014 based on all Lidar sites of atmospheric boundary layer height shows that the boundary layer height of the Jing-Jin-Ji area is between 300~900 m and higher in the southeast.

The use of satellite images to quickly and accurately extract the distribution of the earth′s surface water body has been an important research topic all the time, which has important significance for water disaster monitoring, water resource utilization, etc. The operational land imager (OLI) remote sensing imagery is used to obtain the surface reflectance values of the images by radiometric calibration and atmospheric correction. Then principal components water index (PCWI) is constructed by analyzing the construction method of the typical water index and the principal component space features of ground objects. Taking Poyang Lake as the research area, two different time OLI images are selected during the dry season to extract water body information by using PCWI. The overall accuracy is 95.92% and 95.52% respectively. Compared with the water body extraction effects of other existing five typical water index, the overall effect of water extraction based on PCWI for the two different time OLI images is the best. In conclusion, PCWI of water extraction is feasible and effective.

For the real-time wavefront reconstruction method with the eigenfunctions of Laplacian in adaptive optics based on grating wavefront curvature sensor, three basic parameters including the selected light spot size and the position deviation on photoelectric detector, and the influence of the number of eigenfunctions modes on the precision of wavefront reconstruction are analyzed. The results show that the selected light spot size on the photoelectric detector has an obvious effect on the wavefront reconstruction accuracy, which can be obtained by the ring energy ratio. Because of other diffraction orders light on photoelectric detector, the position deviations of the light spot induce not only the wavefront tilt error but also other wavefront errors. The mode coupling due to the limited resolution can significantly affect the accuracy of the wavefront reconstruction when using too many modes, and the optimal mode number can be estimated via the correlation coefficient between modes.

Beam wander and beam spreading are two important effects for beam propagation in the atmospheric turbulence. Collimated Gaussian beam propagation experiments by means of CCD technique are conducted under the sea, the beach and the road surface environments in the region of Yantai. Beam wander, beam spreading and refractive index structure parameters are measured, and the characteristics of beam wander and beam spreading are analyzed based on measured data. The results show that the fluctuating amplitude of beam spreading and beam wander is the largest on the sea when the refractive index structure parameter changes a little. The fluctuating amplitude of them is 0~1.5 cm and 0~0.6 cm, respectively. The relative error of beam spreading on the beach surface is the least, and it is less than 10%. The refractive index structure parameter on the road can be one order larger than those on the sea and on the beach. The variation tendency of beam spreading and beam wander is the same as that of refractive index structure parameter.

Beam spreading near the sea surface environment is measured in the experiment by dynamically-tested atmospheric beam system. Comparative analyses are then conducted between the experimental data and the theoretical value of both the marine power spectrum and the traditional Kolmogorov power spectrum. Results show that the measured ampltude fluctuation of beam spreading is lager than those of the marine power spectrum and Kolmogorov power spectrum, and the theoritical value of beam spreading for marine power spectrum is small when the measured inner scale is used to calculate. The beam spreading model for the marine power spectrum is closer to the experimental data than that for the Kolmogorov power spectrum with the increase of the refractive index structure constant of atmosphere. The difference between the theoretical value of the marine power spectrum and the experimental data is about 0.1~1.5 cm at 1 km link distance and 0.1~1.8 km at 2 km link distance. Both the relative errors are within 0.1% ~11.4%.

In order to obtain the detailed distribution information of background radial brightness, the measuring method of ground-based whole sky background radiance spectra is developed based on the fiber optical spectrometer and two-dimensional turntable. It can realize the fixed point observation and scanning all the sky. Structure of system, scheme of data detection, principle and method of calibration are introduced in detail. After one scanning, 649 samples of radiance can be obtained. Spectral resolution of each sample is 0.5 nm. Measuring position of each sample is used as pixel and each wavelength radiance of the position is used as gray level. The distribution of whole sky background radiation spectrum band is obtained. The proposed method provides more detailed information for further scientific research.

The influence of sky background radiation on bit error rate (BER) under on-off keying (OOK) modulation is studied, and the simulation method of sky background radiation received by the communication terminal is introduced. Simulation results show that when the communication BER is constant, the upper threshold of sky background radiation is related to the received signal optical power and the electrical noise of avalanche photodiode (APD). Direct solar radiation is the major background radiation received by atmospheric laser communication system, and atmospheric scattering,relative to the direct solar radiation, is very weak. When the solar zenith angle is small, the optic axis of the communication terminal can be adopted to avoid certain sun radiation angle, and it is ensured that the BER of the communication system is less than 10-9.

The error caused by aerosol is simulated when ozone is detected with three wavelength dual difference absorption lidar (D-DIAL) and two werelength difference absorption lidar (DIAL). The effects of the aerosol parameters on ozone detection are analyzed, including wavelength exponent and aerosol content. The impact of the factor C, which is introduced by the elimination to the scattering and extinction errors, on the detection results is discussed by using the three wavelength dual differential method. It shows that C optimal values make the error close to zero, and the optimal value of C is simulated. Different wavelengths are used respectively to simulate the error in multi wavelength difference absorption lidar on ozone detection. In the troposphere, the wavelengths of 266 nm and 308 nm (in DIAL), and 266, 289, 308 nm(in D-DIAL) are used, and in the stratosphere, the wavelengths of 308 nm and 351 nm, and 308, 339, 351 nm are used. The simulated results show that when aerosol scattering ratio R is 2, the error of D-DIAL method is less than 1%, and the error of DIAL method is 10%~45%. In the same aerosol content, the error of stratospheric ozone is significantly less than the error of tropospheric ozone. When the aerosol content is high, the error of D-DIAL detecting tropospheric ozone can reach 6%, and in the stratosphere the maximum error is only 3.5%.

Dark channel prior has a good effect on haze removing. A visibility measurement method based on dark channel prior is proposed, which can overcome the disadvantages of high cost and difficulty in building up of the meteorological visibility meter. The proper target region is selected by analyzing different regions of the image so as to estimate transmittance. A more accurate transmittance is obtained by haze removal parameter optimization and guided filtering refinement, and then the atmospheric extinction coefficient and visibility are inferred. Comparing the results of dark channel prior with the data measured by forward scattering meter (CJY-1G), the error is within ±15%, which meets the application requirement of World Meteorological Orgnization.

In order to study the differences of attenuated backscatter characters of global clouds and aerosols obtained from the cloud-aerosol lidar with orthogonal polarization (CALIOP) the latest version of Version 4(V4) and Version 3(V3) products separately, and the potential impacts on previous studies. The CALIOP two vertical products in January, April, July and October of 2011 are used to gather probability distribution statistic of clouds or aerosols 532 nm total attenuated backscatters, 1064 nm attenuated backscatters and total attenuated color ratios respectively below the altitude of 20.2 km all over the world. And the relative deviation of two different versions of the corresponding data is made statistical analysis. The results show that the relative deviations of the attenuated backscatters between V4 and V3 products for clouds and aerosols tend to be positive values, and the changes from V3 to V4 data are more obvious at nighttime than those at daytime for both clouds and aerosols. The mean relative deviations from V4 and V3 of clouds daytime 532 nm total attenuated backscatters, 1064 nm attenuated backscatters and total attenuated color ratios are 3.40%, 4.66% and 1.18% separately, and those of clouds nighttime data are 2.80%,8.00% and 5.33% separately. The mean relative deviations of aerosols daytime 532 nm total attenuated backscatters, 1064 nm attenuated backscatters and total attenuated color ratios are 1.14%,6.94% and 5.62% separately, those of aerosols nighttime data are 3.33%, 10.92% and 7.64% separately.

The anti-jamming capability of seekers has been one of the most important performance indexes to appraise the missile. Anti-jamming strategies of ladar/infrared (IR) composite seeker are proposed for the common smoke-screen jamming. Based on the analysis of interference mechanism, the impact on transmittance and range is calculated with respect to IR channel and ladar channel, respectively. The anti-jamming strategies and available problems of IR seekers are analyzed, then the composite anti-jamming strategy with target range information is proposed.

The fundamental structure of all-optical dual-hop free-space optical communication (FSO) system is presented and the composite fading channel model which includes atmospheric loss, atmospheric turbulence and pointing errors is established. In the full channel state information relaying, subcarrier intensity modulation is adopted. The closed-form expressions for outage probability and bit-error rate (BER) of dual-hop FSO systems are derived, based on the effects of background noise and amplified spontaneous emission noise. Then the outage probability of dual-hop FSO system is compared with that of the direct link. The effects of the parameters, such as signal-to-noise ratio, the average transmitted photon count of the source node (SN) and optical degree-of-freedom, on the outage probability and bit-error rate are also researched. The results show that all-optical dual-hop relaying can significantly improve the performance of the systems.

Based on the radiative transfer theory, the polarized light scattering characteristics of sea spray in an atmosphere-ocean system by sunlight is studied based on the matrix operator method. The whole atmosphere layer is divided into many sub-layers in the vertical direction, and the vertical distributions of the atmosphere molecular, clouds and aerosol are considered. The ocean surface is dealt as the wind-generated rough ocean surface, and the wave slope distribution and the shadowing effect of the ocean wave are considered. The ocean body is divided into many plane parallel sub-layers, and the absorption and scattering characteristics of sea water and the chlorophyll are considered by an empirical model. The reflection and transmission matrices and source vectors are obtained for each atmospheric or oceanic layer though the discrete ordinate solution. The scattering characteristics of the whole atmosphere- ocean system are constructed using the matrix operated method, which combines the radiative interaction between the layers. The sensitivity studies for the reflected solar radiation by the whole atmosphere-ocean system are conducted for various solar wavelength, incidence solar zenith angle, observation angle, ocean-surface wind speed, the optical thickness of the clouds and aerosols, and the absorption of the gas. The simulation results show that the multi- wavelength and multi- angular polarization information are sensitive to the varies of the atmosphere and ocean surface conditions. The reflected solar radiative intensity and the polarization degree can be combined to retrieve the aerosol information.

The Aerosol extinction coefficient is of crucial importance for atmospheric visibility and climate change.The aerosol extinction coefficient is measured based on the cavity ring down spectrometer using 532 nm pulsed laser.The detection limit of the aerosol extinction spectrometer is 0.3 Mm-1. Pure CO2, pure Freon R134, and different concentration NO2 are used for full scale calibration. Comparative field measurement of aerosol extinction using aerosol extinction spectrometer, nephelometer and aethalometer are carried out, and the data are in good agreement.

Laser beam shaping system based on deformable mirror has the advantages of control flexibility, good adaptability and high damage threshold. In order to enhance performance of the laser beam shaping system with a deformable mirror as the phase modulation element, a stochastic parallel gradient descent algorithm is proposed to further optimize control voltage, which takes the least square fitting control voltage as the initial value. Laser beam can be transformed to square and circular flat topped beam with different sizes by a 37 element deformable mirror. Numerical simulation results show that, for the far field intensity, both the uniformity of target area and the similarity to the theoretical intensity are improved, after the introduction of optimization algorithm, on the basis of the least square method. So the performance of the laser beam shaping system is also improved.descent algorithm

Because the signal attenuation is great in sea channel so as to seriously impact on the performance of communication system, an excellent error correcting code is necessary to reduce the error rate of data transmission in underwater optical communication. A system model of underwater optical communication is established by combining low density parity-check code with pulse position modulation. A simplified soft demodulation based on the general PPM soft demodulation is used to reduce the complexity of the algorithm, which is convenient for hardware implementation. What's more, the simplified soft demodulation method is very suitable for the extraction of soft information in sea channel because it does not need the detailed features of channel. The error performance between the general method and simplified method is analyzed by using Matlab software. According to the simulation results, the system code gain by using simplified method is decreased because of the simplified extraction of soft information, but it is still higher than code gain of the uncoded system. When PPM order is lower, the performance by using simplified method is even superior to that by Solomon Reed code. On the whole, the scheme of the simplified soft demodulation based on the combination of LDPC and PPM is very suitable for underwater optical communication in huge ranges of applications.

Solar spatial position is a very important navigation information in the field of navigation by using atmospheric polarization pattern. And how to get the solar spatial position is very important in navigation. A method based on Rayleigh atmosphere polarization pattern and K-means clustering algorithm is introduced to calculate the solar spatial position. The atmospheric polarized model of skylight is established on the basis of the Rayleigh scattering theory of atmosphere. According to the basic regularities of atmospheric polarization pattern, data of the polarization (DOP) are analyzed by the method of K-means clustering algorithm. The problem of solving position of the sun is transformed into the problem of solving the center of K-means cluster. Finally, the simulation experiment and practical experiment are carried out to verify the algorithm. The experiment shows that, at different times of the same day under clear weather, the errors of the solar position and altitude angle are all less than 0.01°. The algorithm error is smooth, and the relative error can reach higher precision. The solar spatial space can be effectively solved by atmospheric polarization pattern.

Laser communication is a new hot spot in underwater wireless communication. It′s the key in channel research to evaluate the laser transmission attenuation under seawater environment accurately. A new remote sensing inversion algorithm is proposed by synthesizing the existed QAA-RGR (Quasi-Analytical Algorithm Red-Green-Bands-Ratio) remote sensing inversion algorithm and the national satellite ocean application service (NSOAS) model, which can evaluate the attenuation coefficient spectra based on moderate-resolution imaging spectroradiometer (MODIS) land bands data directly. Compared the absorption coefficient spectrum and scattering coefficient spectrum, which is estimated by inversion algorithm with MODIS L2 level data, the feasibility of the inversion algorithm is verified. It is important to analysis and understand the optical properties of seawater at coastal areas dynamically.

Continuous faceplate discrete actuator deformable mirror (CFDA-DM) is the most important device in adaptive optics. In high power laser systems, this kind of deformable mirror (DM) is apt to produce thermal deformation, which can seriously affect the compensation ability of DM and the output beam quality. Experimental platform is set up to study DM thermal deformation. In the experiment, when DM is continuously irradiated by 2.5 kW laser for 130 s, the peak-to-valley value (dPV) of wavefront increases from 0.0806λ (before irradiation) to 0.5423λ, the higher order aberration of faceplate is 0.1220λ, and the low order aberration is mainly defocus and astigmatism. After dPV of a zero degree astigmatism is compensated from 0.4853λ to 0.0707λ, DM is irradiated by 2.5 kW laser for 180 s again. In consequence, the dPV of wavefront increases from 0.0707λ to 0.7548λ, and the higher order aberration of wavefront is 0.2487λ. The above results show that the thermal deformation does not only lead to lower order aberration, but also produce higher order aberration, which cannot be compensated by DM itself. The higher order aberration is the key factor that influences the output beam quality of high power laser systems.

The traditional wavefront retrieval method uses wavefront slope or curvature calculated from the obtained light intensity information to reconstruct wavefront. More light field information is contained in the light intensity information obtained from the structure based on micro lens array. Based on micro lens array structure, the four-dimensional parametric characterization and the space-space frequency information acquisition and reconstruction of light field are analyzed. The corresponding relationship between the joint distribution of the light field space-space frequency and the Wigner distribution function is established. A Hartmann phase retrieval method based on the light field information is proposed. A numerical calculation model is established and a simulation is carried out. The simulation results show that the proposed phase retrieval method, which uses the light field space-space frequency joint distribution based on light intensity information, can reconstruct phase for low-order aberration effectively and quickly, and the error is small. The proposed method has wide application prospect in aberration compensation of optical imaging system.

The adaptive optics (AO) system involves many fields like optics, electronic control and so on, so it is necessary to improve the reliability of the electronic control system. The fault tree analysis (FTA) method introduced, and the key modules, such as the wavefront detection unit, wavefront processing unit, are analyzed.A fault tree model of the system is established. The minimum cut sets of system are got through qualitative analysis. Similarly, the probability of failure of the system and the order of the importance of bottom incident are got through quantitative analysis. According to the result, the stability of system can be improved and the design of system can be optimized effectively.

The restraining of water backscattering and increasing target resolution are the key technologies in underwater lidar detection. An adaptive filtering method of target echo based on recursive least- squares (RLS) algorithm is proposed. Through the feature analysis of underwater lidar detected signal, the forgetting factor in traditional RLS algorithm is improved to distinguish the target echo and water backscattering signal. The improved forgetting factor can also adapt the echo amplitude changes in different target distances. To estimate the effect of the method, the underwater detection experiments are carried out in water basin under different target distances. The results show that the backscattering signals are suppressed and the target echo are extracted with high tracking and convergence speed by using the proposed variable forgetting factor RLS algorithm. Compared with the traditional methods, the resolution of the processed target echo signal is increased and the proposed method has great advantage in the weak target echo extraction. Finally, the impact of filter order on algorithm processing results is discussed.

As one of most important simulation methods,hot air convection atmospheric turbulence simulator has been widely used in many area.However,there is rarely study on the spectral characteristics and probability density characteristics of the simulated turbulence.A long-term measurement is made in a real link under 1 km and 6 km atmospheric environment,and a simulate link by using the same laser emission device and measuring device.The detailed analysis of the spectral characteristics and the probability density fluctuations characteristics of the simulator are done.The experimental results show that compared with the real atmosphere,the spectral characteristics and the probability density fluctuations characteristics of scintillation generated by the convection atmospheric turbulence simulator are well agreed to the real atmosphere.For angle-of-arrival,the spectral characteristics and the probability density fluctuations characteristics are well agreed to the real atmosphere on y axis.But on x axis,because of the lack of crosswind,the spectral characteristics is different from real atmosphere.For probability density fluctuations characteristics,there is no obvious pattern.

Based on the extend Huygens-Fresnel principle,the analytical expressions for cross-spectral density matrix elements of random electromagnetic Sinh-Gaussian (ShG) beams as typical stochastic electromagnetic beams propagating through atmospheric turbulence are derived,and used to study change in the transverse degree of polarization of random electromagnetic ShG beams propagating in atmospheric turbulence.It is shown that distribution of transverse degree of polarization varies with location when random electromagnetic ShG is propagating in atmospheric turbulence.The smaller the structure constant C2 n ,the larger the Sh-part parameter Ω0 ,or the bigger the spatial correlation length σxy (σyx ) ,the longer the propagation distance of distribution of polarization into bimodal shape,flat shape,unimodal shape.

Based on the theory of generalized Huygens theory and the unified theory of coherence and polarization, distribution of the intensity of partially coherent radially polarized beams influenced by source wavelength, and degree of polarization (DOP) influenced by coherence, atmosphere turbulence intensity, spot size and source wavelength, are investigated while propagating in turbulent atmosphere. It is shown that while the partially coherent radially polarized beams propagate in turbulent atmosphere, the distribution of intensity is affected by source wavelength obviously. With the increase of propagation distance, the doughnut beam spot of the partially coherent radially polarized beam becomes a solid beam, which is related to source wavelength. The shorter the source wavelength is, the longer distance the partially coherent radially polarized beam propagates to form a solid beam shape. In addition, distribution of DOP is also affected by coherence, atmosphere turbulence intensity, spot size and source wavelength. At a certain propagation distance, the rate of DOP with radius increases with the larger original coherence, the weaker atmosphere turbulence intensity, the bigger spot size and the shorter source wavelength. Such tendency becomes more obvious with longer propagation distance.

The propagation characteristics of terahertz (THz) wave in the turbulent atmosphere are very important to the space applications of THz wave. The horizontal propagation characteristics of THz wave in atmospheric turbulence have been studied by the random phase screen method. Through ignoring the scattering and absorption of THz atmospheric conditions and focusing on the atmospheric refractive index fluctuation, the average intensity distribution and scintillation indexes on the receiver plane were studied under different propagation distances in the atmospheric turbulence. For comparison, the visible light waves were also carried out through numerical simulation and analysis under the same conditions. The results show that under the same conditions, the influence of atmospheric turbulence on THz wave is much smaller than it on the visible light wave. Furthermore, atmospheric turbulence has little impact on the short-range application of THz wave.

Based on the theory of generalized Huygens-Fresnel and the cross-spectral density matrix,the analytic expressions of mean-squared beam width of partially coherent radially polarized (PCRP) beam and Gaussian Schellmode (GSM) beam in atmospheric communication are derived.By comparing the influence of turbulence,coherence length and source wavelength on the spreading of width and angular between the two kinds of beams,it shows that the PCRP beam has superiority in atmospheric communication than GSM beam.The result shows that the propagations of the PCRP beam and the GSM beam in turbulence follow the same rules.The larger the turbulence is,the larger the spreading of width and angular is.The larger the coherence length is,then the more the effect of turbulence on the PCRP beam is,the smaller the angular spreading is.The larger the source wavelength is,then the less the effect of turbulence on the PCRP beam is,the larger the angular spreading is.But the PCRP beam is far less affected by turbulence,coherence length and source wavelength than the GSM beam,which means the spreading of width of the GSM beam is larger than that of the PCRP beam.In addition,the spreading of angular of the GSM beam not only relates to the three parameters above,but also is affected by the width of the source beam which is nothing to do with the spreading of angular of the PCRP beam.The above conclusions show that the PCRP beam is more beneficial to atmospheric communication than the GSM beam,and the study about turbulence,coherence length and source wavelength has a guiding role for the application of PCRP beam in atmospheric communication.

Adaptive optics (AO) technology is an effective way to alleviate the effect of turbulence on free space optical communication (FSO). A new adaptive compensation method can be used to optimize the communication performance without a wave-front sensor. The application process of the wavefront sensorless adaptive optics on FSO is simulated using the application of differential evolution (DE) algorithm, stochastic parallel gradient descent (SPGD) algorithm and simulated annealing (SA) algorithm. Meanwhile, the wavefront correction capabilities are analyzed by comparison of the coupling efficiency, the error rate and the intensity fluctuation under different turbulence intensities before and after the correction in FSO system. The simulation results show that the three algorithms can effectively improve the communication performance of FSO systems, especially the DE algorithm with lower iteration rate but optimal effects. Therefore, DE is suitable for strong turbulence conditions.

Using high-speed,multi-cell Shack-Hartman wave-front sensor,the measurement of temporal and spatial feature to a rolling phase screen laboratory atmospheric turbulence generator is presented.In terms of spatial feature,coherence length of the atmospheric turbulence and phase spatial structure function of the wave-front are calculated,and the variance distribution of the wave-front Zernike coefficient is compared to the theory as well.In addition,on the temporal feature,the Greenwood frequency and time power spectrum of the simulated turbulence are analyzed.A new method that is called residual variance algorithm to calculate the time constant is proposed.The result shows that the atmospheric turbulence generated by the rolling phase screen is consistent with the Kolmogorov turbulence.

The aerosol measurement by micro-pulse lidar(MPL) system is taken in Nanjing Comprehensive Observation Base of China Meteorological Administration in the north suburb of Nanjing. The variation of aerosol extinction coefficient profiles and depolarization ratio profiles indicate that the depolarization ratio of aerosols in clear atmosphere, mist and water cloud have similar values, but the value of ice cloud depolarization ratio is larger than all of them. Nearly 50 times inversion results of experimental data during January to June in 2009 show that the depolarization ratio is concentrated between 0 to 0.05 when the height of cloud base is below 4 km. While the height is above 4 km, this value is almost between 0.05 to 0.15. The higher of height cloud base is, the higher of the probability of larger depolarization ratio values is appeared. Comparing the inversion results of summer mist and winter dust in 2012, the results show that dust appears obvious boundary, while the characteristics of mist boundary is blurred. Dust's outbreak and dissipate can be monitored by combining spatial distribution and temporal distribution of extinction coefficient with change of depolarization ratio. Comparing the results of MPL and CE-318 sun photometer, the optical thickness of both instruments measured is consistent with the trends of time.

Based on the extended Huygens-Fresnel principle, the propagation properties of electromagnetic Gaussian multi-Schell model beams through atmospheric turbulence in a slanted path are investigated in detail. Results indicate that the changing of transverse coherence length has an effect on the far-field intensity distribution and the beam width induced by atmospheric turbulence of the laser beam. Besides, the degree of polarization of the electromagnetic Gaussian multi-Schell model beams can change with the propagation distance, and it can reach a certain value when the laser beam propagates through atmospheric turbulence in a slant path. This result indicates potential applications for satellite-to-ground or ground-to-satellite laser communications.

The expression for the Rayleigh range of partially coherent annular beams propagating through non-Kolmogorov turbulence is derived, and the influence of turbulence parameters (generalized exponent parameterα , inner scale l0 , outer scale L0 ) and the beam parameters on the Rayleigh range is studied. It is shown thatRayleigh range zR| turb in turbulence decreases with increasing intensity of turbulence, and is always smaller than Rayleigh range zR| free in free space; zR| turb decreases with increasing L0 (just for 3.6 < α < 4 ) and increases with increasing l0 ; zR| turb does not monotonically vary with the increase of α , namely, it decreases firstly and then increases due to increasing α . When α = 3.11 , zR| turb reaches its minima. Additionally, the influence of turbulence on the Rayleigh range increases with increasing coherence parameter β , beam width w0 and decreasing obscure ratio ε , beam orders M(N ).

By analyzing the ultra fine atmospheric CO2 absorption spectrum, the infrared laser wavelength can be choiced for detecting the atmosphere CO2 concentration. It can provide the basis for a wide spectrum infrared lidar. The spectrum of wide spectrum infrared laser is much wider than the differential absorption lidar, and it has no use for high frequency locking technology. Also, this technology can avoid differential absorption lidar measurement error by the on wavelength shift. By analyzing the water vapour absorption spectrum, super luminescent diode (SLED)′s luminescent spectrum and InGaAs infrared detector′s response spectrum, the wide spectrum laser center wavelength is 1572 nm and the spectral range is 1568~1575 nm in theory. By the experimental laser source,the results show that the center wavelength is 1571 nm, the spectral range is 1564~1578 nm, the output power is 0.01 mW. This laser can avoid the influence by the water vapour absorption, and it is simple, low cost and easy to build. It can help for the development of the atmosphere CO2 concentration detecting by the wide spectrum infrared lidar.

The infrared radiation characteristics of the environment for spacecraft play a significant role in the infrared characteristics of the spacecraft. Thus the study on infrared radiation of aircraft background is essential. The regime which only consists of the regional atmospheric climate system in the field is called limb background in the view of the atmosphere system of the earth. Based on moderate spectral resolution atmospheric radiation transmittance algorithm (MODTRAN) atmospheric radiation model, the atmospheric radiation transmission theory is used to establish the limb infrared radiation model. Limb background infrared radiations are calculated at all latitudes in the typical wavelength ranges of 3~5 μm and 8~14 μm , including the seasons of winter and summer. The results show that the main factors affecting the limb background infrared radiation are tangent altitude, latitude, season, aerosol and wavelength range. These provide theoretical supports for the detection of limb background infrared radiation.

To study the relative spreading of truncated Gaussian Shell-model (GSM) beam propagating through non-Kolmogorov turbulence, the extended Huygens-Fresnel principle and integral transform technique are used to derive the expressions for the mean-squared width and relative width of truncated GSM beam propagating through non-Kolmogorov turbulence. The variation of the mean-squared width and relative width versus waist width w0, coherence parameter α , truncation parameter δ and generalized exponent parameter γ are analyzed numerically. The results show the beam spreading is less affected by turbulence with the smaller α and δ , and the influence of non-Kolmogorov turbulence on beam spreading increases first and then decreases due to increasing waist width w0 and γ . The results obtained above are explained physically.

The relationship between aerosol extinction coefficient and PM2.5 mass concentration is analyzed, it is proposed that the PM2.5 mass concentration profile can be retrieved by combining the side-scatter lidar system based on charge-coupled device (CCD) and PM2.5 detector. From case study, when the variation of relative humidity is small, PM2.5 mass concentration is proportional to aerosol extinction coefficient at ground. The characteristic of PM2.5 mass concentration profile of near-ground on April 13, and December 16, 2014 at Dongpu island of western suburb of Hefei city is analyzed as changing with time, changing with altitude, and air pollutant concentration is comparatively large in close surface. The experimental results show that the side-scatter lidar system based on CCD combined PM2.5 detector is an effective new method of exploring pollutant mass concentration profile in near-ground.

HCl gas is one of the waste incineration emissions. It does not only corrode the incineration equipment and monitoring instrument, but also harms human health. Effective online monitoring of the HCl gas concentration ensures normal use of the incineration equipment and function of the monitoring instrument. An online HCl concentration analyzer based on tunable diode laser absorption spectroscopy (TDLAS) is presented. The laboratory tests show that the linearity error of the analyzer is not higher than ±1% F.S and the stability of the analyzer is good. The analyzer has been successfully applied to the exhaust vent of a waste incineration equipment for continuous monitoring. The results show that the 1.742 μm absorption spectrum can be used to measure HCl concentration. The analyzer has the advantages of short response time, high reliability and the measurement does not be interfered by background gas, dust and window stains.

The surface morphology and deformation depth of the copper targets treated by nanosecond laser shock peening (LSP) are measured by optical microscope (OM), 3D profile and so on. Non-contact optical profile is used to measure the surface roughness of the metal targets. The source of micro defects is analyzed emphatically when absorption layer is aluminum foil tape. Samples with different surface roughnesses are treated by LSP. Experimental results show that there will form macro dents and micro convex-concave structures on the impacted regions when black paint is used as the absorption layer. When the absorption layer is aluminum foil tape, besides the macro dents, there will form large amounts of micro defects on the impacted region. Through analysis and experimental research, it is confirmed that the formation of micro defects are associated with the air bubbles existed in the glue on the back of aluminum foil tape. LSP can increase the overall roughness but reduce the maximum height of roughness when the original roughness is high. When the surface smoothness is high, LSP can increase the overall roughness and the maximum height of roughness.

In order to evaluate the performance of the convection turbulence simulator, the stability of the simulate turbulence is tested and the credibility of the turbulence simulator is improved. The measurement and analysis are done from three aspects of regional stability, wavelength stability and frequency stability by using specific instrument. 21 points in specific locations are chosen for testing the regional stability of scintillation and angle-of-arrival. By using the coherence length as the indicator, 532 nm, 808 nm, 1064 nm and 1550 nm lasers are used to test the wavelength stability of the convection turbulence simulator. Finally, the spectra of scintillation and angle-of-arrival are analyzed to test the spectral stability of turbulence simulator. The experimental results show that, the performance fluctuation of the convection turbulence simulator in a 16 cm ×16 cm area is less than 15%, the coherence length fluctuation under four wavelengths meets Kolmogrov theory and the spectrum fluctuation is less than 20%. The turbulence simulator can simulate the atmospheric turbulence with high precision, high reliability and high stability. The research provides a strong support for the applications of the convection turbulence simulator.

Seawater is a complex system, which involves variety of organic, inorganic, dissolved and suspended substances. However, the main components in seawater are the inorganic salt, such as NaCl, MgCl2, KCI, NaHCO3, MgSO4, and so on. These elements have a big influence on laser′s transmission underwater. To further understand the optical properties of seawater, the transmittance in these salt waters with different concentrations of salt is measured. The transmission spectra of dissolved substance solution is measured by ultraviolet- visible- infrared spectrophotometer. The transmission characteristics of different salt waters are studied by using the wavelength of 450, 532, 633 nm lasers. Then a first- order exponential curve is gotten from experimental data, which shows the relationship between transmittance and the conductivity in different solute concentrations. From the figures, a conclusion that transmittance decreases with the increasing of concentration is gotten. With the same transmission distance and different concentrations, the attenuation characteristics of light are different. The work is hoped to be helpful for the research about underwater target detection and laser communication in the sea.

Direct wavefront gradient algorithm directly establishes correspondence between measurands of the wavefront sensor and response characteristics of the deformable mirror. The voltage can be directly calculated by the algorithm. We use Hartmann wavefront sensor with 64 sub-apertures to detect the distorted wavefront. Based on the hypothesis that of deformable mirror is the weighted addition of the influence function, each of the voltage values applied on the drive is solved by the algorithm. The simulated 32 units of deformable mirror can be controlled and then distorted wavefront can be restored. The simulation result shows that direct wavefront gradient algorithm can effectively adjust the distorted wavefronts.

There exist various of fog drop size distributions in advection fog and radiation fog, which result in the different attenuation performances as light propagates in fog field. Mie theory can describe the scattering and attenuation of aerosol particles in fog field, while light propagation follows the principle of dynamic particles conservation. In this paper, fog drop size distribution is applied to modify the scattering phase matrix of aerosol particles, and the scattered light′ s polarization can be solved when infrared light penetrates into aerosol particle clusters. The results show that aerosol particles′ depolarization mainly depends on fog drop size distribution, fog drop refractive index, absorption coefficient and incident wavelength. In the forward-scattering area, depolarization decreases as visibility increases, while the opposite trend occurs in most backwardscattering area.

Optical property of phytoplankton is studied based on the physical and biological properties in China Sea. A new algorithm, combined with global system for mobile communication model and fluorescence model, is applied to retrieve the phytoplankton information. In the algorithm, twice optimization procedure is performed to get the best results. This combined algorithm is applied to simulate the underwater light field by using Hydrolight. The comparison of the sinulation results and synthetic data shows that the algorithm is effective to retrieve the optical information of phytoplankton. In addition, by using optical satellite data (MERIS) and the dynamic parameters, the impact of NALGAE on phytoplankton distribution is analyzed. The result shows Ekman pumping is one of reasons for the ocean color anomalies.

Based on the non-Kolmogorov spectrum, using the extended Huygens-Fresnel principle, the analytical expressions for the spectrumof Gaussian-Schell model (GSM) beams propagating through non-Kolmogorov atmospheric turbulence are derived and used to study the influence of non-Kolmogorov atmospheric turbulence on spectral changes of GSM beams. It is shown that there exist spectral shifts (blueshift and redshift) and spectral transition of GSM beams propagating through non-Kolmogorov atmospheric turbulence. The spectral transition depends on the off-axis distance r, the general exponenta, the general structure constant [C2n], the inner scale l0, the outer scale L0, and the propagation distance z. With the increment of the general exponenta and the inner scale l0, as well as the decrement of the general structure constant [C2n], the spectral transition magnitude [Δ] will decrease and the critical position of spectral transition zc will increase. This work will provide theoretical model and computational basis for researches such as free space optical communications.

Gamma-Gamma model is a commonly used intensity scintillation model in wireless optical communications. For the problems of the complexity of the parameters models and the lack of reference for various approximate models, under Gaussian beam and using the method of simulation calculation, we analyze the effects of waveform condition, aperture dismeter, transmission distance, inner/outer scale, turbulent strength and wavelength on the characteristics of Gamma-Gamma model. The simulation results show that the effects of waveform condition, aperture diameter, transmission distance and turbulent strength cannot be ignored, while the effects of inner and outer scales, wavelength can be neglected. Moreover, as long as the ratio of aperture diameter to transmission distance remains unchanged, the Gamma-Gamma distribution characteristics will also keep unchanged. These conclusions provide reference and basis for the simplification of models in practical applications and the setting of system parameters for actual system.

Cirrus has the effect of radiative forcing which is influenced by the microphysical properties of cirrus. An algorithm for retrieving the microphysical properties of cirrus based on micro-pulse lidar and millimeter wave radar is presented. In the algorithm, lidar extinction coefficient retrieved from backscatter signal intensity and water equivalent radar reflectivity factor are combined to obtain cirrus-cloud ice water content (IWC) and general effective size (GES). A cirrus case in Shouxian is analyzed using the proposed algorithm and the data from micro-pulse lidar and millimeter wave radar. The results show that the IWC and GES are 10-3~10-1 g/m3 and 1~200 μm, respectively, which are consistent with the empirical values. The changes of IWC and GES with time are in accordance with the evolutions of cirrus. The analysis results imply the feasibility of retrieving microphysical properties of cirrus from micro-pulse lidar and millimeter wave radar data.

The propagation of Laguerre-Gaussian beam in intermediate fluctuation turbulent atmosphere is studied. Using the split-step Fourier method and the phase screen method, the intensity distribution, phase distribution and the spectrum distribution of LG beam are simulated in the case of up-downlink communications path and level communication path respectively. It is found that the atmospheric turbulence will induce the spread of the spiral spectrum. With the increase of the topological charge and refractive index structure constant, the spectrum spread becomes more serious. It is also concluded that the influence of the atmospheric turbulence on the Laguerre-Gaussian beams is smaller in up-downlink communication path than in level communication path.

A polarization sounding scheme of airborne lidar is proposed, in which the polarization sounding “bottle-neck” channel i.e., the perpendicular sounding channel in the traditional scheme is obliterated. Return signal differences between 532 nm depolarization sounding channel and 532 nm polarization parallel sounding channel can be minished in the polarization sounding courses. The energy ratio of two channels, return signals can be adjusted. This scheme strengthens the polarization sounding capacity when it has the same energy as first scheme. It can reduce the photomultiplier (PMT) saturation probability when cirrus is sounded by 532 nm polarization channel. This scheme also can reduce laser energy and actualize genuine 532 nm and 1064 nm dual-wavelength sounding.

Three-dimensional (3D) distribution of two-dimensional (2D) Mie scattering phase function is presented in the spherical coordinate system with the linearly and circularly polarized incident light. By using the program of Monte Carlo simulation of polarized light propagation, 2D distribution models of elements of backscattering Mueller matrix and degree of polarization (DOP) from bubbles film of ship wakes are simulated. The relation between scattering coefficient and the thickness of bubbles film is studied. The results show that spatial distributions of DOP have the properties of azimuth selection, and the polarization-maintaining characteristic of circularly polarized light is better than that of linearly polarized light. With the thickness and scattering coefficient of bubbles film increasing, the DOP of linearly polarized light gradually decreases, while the DOP of circularly polarized light first rapidly increases to a maximum and then slowly decreases.

Because laser diode ceilometer′s backscattering signal is weak and easily disturbed by various noises at the same time, the most important task and difficult point for the signal detection of laser diode ceilometer is how to take effective measures to remove the noise in the backscattering signal. In view of the redundancy reduction capability of the independent component analysis (ICA), fast ICA is proposed to eliminate noise of laser diode ceilometer′s return signals. Since fast ICA requires multi-channel signals, the continuous multiple groups of laser diode ceilometer return signals are used to construct the multi-channel signals, and then the blind source separation (BSS) of fast ICA is applied to the signals. Thus, the virtual sources are extracted one by one, and the noise embedded in the observed signal is removed. The experimental results demonstrate that the method has good effect on removing the noise from laser diode ceilometer′s return signal. Such a fast ICA algorithm has the practical value in processing laser diode ceilometer′s return signals.

According to the high bandwidth, low packet-loss ratio, high channel utility requirements of satellite optical switching network, an on-board assembly algorithm based on mixed threshold and round-robin scheme is proposed combining the ground optical assembly algorithm. The algorithm caches the IP packet according to the parity, and assembles the packet according to the mixed threshold and round-robin scheme. Through the scheme, the padding ratio of burst is lowered. From the results of analysis and emulation, it is found that the complexity is the same as that of the round-robin method; the padding ratio of burst data packer is less than 10-4 when the load is 0.65, and the packet loss rate is 10-6 when the load is 0.5. This algorithm meets the requirements of optical satellite communications.

Bandwidth of adaptive optics (AO) system based on stochastic parallel gradient descent (SPGD) algorithm is analyzed theoretically and experimentally. The relation between convergence speed and control channel number of AO system based on SPGD algorithm is researched. Then the bandwidth of AO system based on SPGD is analyzed theoretically by comparson with the traditional AO system with the Hartmann-Shack (H-S) wavefront sensor. A dynamical wavefront distortion correction experiment is performed, and the experimental results verify the theoretical analysis results well. This research can provide a basis for the design and use of AO system based on SPGD algorithm.

Salinity is an important physical oceanographic parameter which influences many processes in the ocean. A multi-linear regression model and artificial neural network are developed for sea surface salinity and tested against in situ measurements in the Bohai Sea. The models are validated by in situ data. The root mean square errors are 0.858 psu and 0.689 psu (psu stands for practical salinity unit) with the correlation coefficients of R2=0.81 and R2=0.82, respectively. Then the model is applied to MERIS data to derive sea surface salinity map which can generally characterize the spatial pattern of sea surface salinity of the Bohai Sea. Both models are suitable for multi-spectral remote sensing data.

In order to restore turbulence-degraded images exactly and rapidly, an iterative blind deconvolution (IBD) algorithm in the frequency domain based on temporal signature is proposed. The temporal signature regularization and Tichonov regularization are incorporated in the cost function. The constraints of non-negativity, energy and bandwidth of the PSFs are added in the iterative blind deconvolution to estimate the object image and point spread functions (PSFs) by the second order conjugation gradient (CG) optimization method. Structure-adaptive applicability filter is used to reduce noise and promote the edges of images. The experimental results show that the proposed algorithm is efficient to recover different intensity turbulence-degraded images and robust with high noise-resisting ability.

The signal-to-noise ratio (SNR) of communication system is variable with channel status and circuits noise. We analyze the turbulence index and irradiance variance, and then establish the relationship between Rytov index of the atmospheric turbulence and SNR of intensity modulation free space optical communication (FSO) system. Firstly, the multiplicative noise induced by irradiance is analyzed. The relationship between irradiance variance and SNR of the FSO system is introduced. Then two common noise models are introduced to simulate the multiplicative noise. The relationship among Rytov index, irradiance variance and SNR of FSO system is derived. At last, the experimental measurement data under different weather conditions are used to prove the simulation results. The results show that there is a linear relationship between Rytov index and variance of intensity in weak turbulent weather. SNR of FSO system relatively decreases as the Rytov index increases. While in medium to strong turbulent weather, variance of intensity converges towards saturation, and SNR tends to a stable value.

In order to study the atmospheric transmission characteristic of 1.54 μm and 1.06 μm lasers and the impact on laser ranging, Modtran is used to simulate the atmospheric transmittance of 1.54 μm and 1.06 μm lasers in different conditions which include atmospheric molecules, aerosol and fog. The laser ranging principle is used to get the relationship between the maximum range of pulse laser rangefinder and atmospheric transmittance. The results point out that, the impact of atmospheric molecules is negligible. Decrement of aerosols to 1.06 μm laser is heavier than that to 1.54 μm laser, and humidity is the key factor. Fog has very heavy decrement to both of the lasers, and they have almost the same atmospheric transmittance in fog. The reduction of visibility has heavy impact to the maximum range of pulse laser rangefinder. Since 1.54 μm laser has better atmospheric transmittance than 1.06 μm laser, pulse laser rangefinder which uses 1.54 μm laser has advantage in the aspect of maximum range.

The research of scattering property of small particles in electromagnetic beams has comprehensive applications in fields such as environmental monitoring. The electromagnetic beam is expanded in series, and the theoretical solutions of the internal fields for small particles as well as the physical significances of the items in these series are developed. Taking the elliptical beam as an example, the internal electric field and the changes of the ratio of the latter item to the former of the series, versus both the distance and the frequency are simulated. The scattering property of small particles in an elliptical Gaussian beam is investigated. By simulations, the effects of the beam waist and the frequency on scattering property are analyzed. The validity of the algorithm used is demonstrated. Results show that the beam waist may improve notably the particle′s identification, the scattering field of higher order item is much smaller than that of lower order item, and the power order of coordinates in the solution of internal field, speaking to a Rayleigh particle, is always equal to that of coordinates in the incident beam. The method used is simple and has explored a new way for scattering from particles in electromagnetic beams.

Using phase-screen approximation, the field distribution of laser beams propagating through atmospheric turbulence is calculated and simulated. The wavefront phase of the distorted beam in turbulence is also analyzed in terms of the high-frequency phase proportion and the number of branch points. Furthermore, considering the coupling between deformable mirror actuators, the model for estimating the physical limit of phase correction is built up by using the method of high-pass filtering including a smoothing factor of mirror actuator. The influence of turbulence intensity and propagation distance on the physical limit of phase correction is analyzed quantitatively. The results show that in a certain range, the proportion of high frequency in distorted phase increases obviously and the number of branch points grows gradually with the increase of turbulence intensity and propagation distance; the correction effect of laser beams in turbulence would be influenced mainly by the proportion of high-frequency in distorted phase and the number of branch points, and the greater the proportion of high frequency phase or the more the number of branch points is, the worse the correction effect of adaptive system would be.

Intensity data acquired by terrestrial laser scanner contains physical and chemical information of objects. The mechanism by which the intensity data are produced is the key point to the analysis and application of intensity data. The working characteristics of terrestrial laser scanners are analyzed, hypotheses are proposed, and the calculating formulation of intensity data is simplified. The conclusion is drawn that reflectivity, incidence angle and range are the three main variables affecting the intensity data mostly. Based on a vertical surface, the distances between adjoined scanning points and influence of angular step width are analyzed and a formulation is proposed to measure a nonuniform distribution of scanning point. By simulating the intensity data of the vertical surfaces, the proposed formulation about intensity data is verified and the influence of the three variables is analyzed.

The influence of weather can deteriorate the performance of free-space optical communication system. Based on the Mie theory and two kinds of raindrop spectral models, the laser attenuation induced by rain with different raining rates is calculated. The laser attenuation due to visibility is calculated using Kim model and AlNaboulsi model. The performances of free-space optical communications in rain and fog weather are studied. The relation between the bit error rate and the transmission range, as well as that between the bit error rate and the transmission power, is analyzed in different raining rates and rain or fog weather condition. The results show that raining rate influences the transmission ranges, and the attenuation induced by fog is much bigger than rain, which leads to a shorter transmission range. To guarantee the normal work of the system, the transmission power can be appropriately increased.

Cirrus cloud has an important influence on the radiative balance in earth-atmosphere system, and cirrus cloud lidar ratio is helpful to understand the optical property of cirrus cloud. The retrieval methods of cirrus cloud effective lidar ratio are introduced, the features and application range of these methods are analyzed, and the reasons of selecting these methods are provided. System errors and random errors of these methods are estimated by case study. The results indicate that these retrieval methods are consistent and effective.

This paper presents the aerosol measurements in north suburb area of Nanjing and the analysis results. The aerosol in north suburb area of Nanjing is measured regularly by Raman-Rayleigh-Mie lidar system, and the results are analyzed. Variation of calculation result of aerosol extinction coefficient with boundary value is discussed in detail. The method for selecting more accuracy boundary value is suggested, and based on which, more accurate aerosol extinction coefficient is obtained. By comparing with other ground-based measurement results, it is indicated that aerosol Raman-Rayleigh-Mie lidar measurement results are comparable, and the method for boundary-value selection and aerosol extinction coefficient calculation is reliable.

A new differential image motion monitor (DIMM) system for measuring atmospheric coherence length which can track motion target is developed. The system uses a new algorithm which is composed of genetic algorithm and iterative centroid algorithm to process differential image and calculate the offset of the target and the covariance of the angle-of-arrival fluctuation in realtime. So, it can track motion targets and measure the atmospheric coherence length. In experiment, we use a halogen lamp tied in a stratosphere balloon at the altitude of 35 km as the lamp-house to measure the atmospheric coherence length along slant propagation path. Simultaneously, we put another instrument 5 m away from the new system which selects the solar limb as the lamp-house to measure the total layer atmospheric coherence length. The result indicates a linear correlation between the two groups of data. At last, we analyze and discuss the feasibility of a method which can use laser guide star to measure the total layer atmospheric coherence length.

Cloud is one of the important factors in the field of meteorology forecasting and navigation and so on. Therefore, it is important to measure cloud. As one of the important meteorological parameters, the cloud cover has become an important part of meteorological observations. So far, the measurement of cloud cover mainly relies on visual observation, which leads to large deviations because of various factors. Measuring the cloud cover is an important application of laser ceilometer. An automatic inversion algorithm of cloud cover of laser ceilometer is proposed in this paper. The purpose of the algorithm is to construct a two-dimensional image of time and cloud height based on the ceilometer measurements only from a single point. The cloud cover is calculated according to the ratio of time occupied by clouds. The comparative experiments show that the algorithm can more accurately calculate the cloud cover information, and it is of great practical value for laser ceilometer.

In the detection of a point source with Hartmann wavefront sensor, besides the normal noise sources such as signal photon noise, readout noise and background noise, the blind pixels existing on the image sensor may also introduce centroid detection error. The integral formula of centroid detection error in the presence of a single blind pixel in the spot area is put forward. Furthermore, analysis about the two influence factors of centroid displacement error induced by single blind pixel, i.e., the distance between single blind pixel and spot center and the Gaussian width of the spot is presented. The simulation and experimental results are in accordance with the theoretical analysis.

Drop size distribution (DSD) observed at the ground depends on complex microphysical processes that progressively transform ice or water clouds particles aloft into rain below. DSD reflects the physics of rain and is the fundamental property for radar rainfall remote sensing, because it rules the relationship between the radar reflectivity factor Z and rainfall rate R. To better understand the microphysics of the summer precipitation, DSD measurements collected with Parsivel disdrometer are carried out at Beijing Weather Observatory in July to August 2007. The DSD characteristics and the relations among the radar reflectivity factor Z, rainfall rate R and mass-weighted mean diameter Dm are investigated. Specific Z-R relationship is derived for the whole data set.

Aiming at the problem that the omnidirectional sea-wave spectrum of fractal sea-wave model cannot satisfy the positive power law when the spatial wave number is smaller than the fundamental wave number, one-dimensional (1D) sea-wave model is proposed by combining statistical sea model and normalized band-limited Weierstrass-Mandelbrot (WM) fractal sea model. With the proposed method, the closed form expression of the omnidirectional sea-wave spectrum is calculated, and the obtained omnidirectional sea-wave spectrum is in good agreement with the commonly used Pierson-Moscowitz (PM) spectrum. The electromagnetic scattering coefficient of the improved model based on two-scale method is derived. The angular distributions of the scattering coefficient of Longuet-Higgins model, classical fractal model and improved model are analyzed. Simulation shows that the difference among the three model′s scattering coefficients is caused by the large scale of sea-wave, which proves the validity of the model. The results are also validated by real data.

In order to use Hartmann-Shack wavefront sensor testing lithography objective lens accurately, two-dimension insert polynomial is proposed to replace Zernike polynomial, which is the basic of modal wavefront reconstruction. The wavefront aberration of a lithography lens is simulated to be the under-test wavefront. The root-mean-square (RMS) value of the reconstruction error reaches 0.0609λ. The possibility of this method is proved. The accurate of reconstruction changes stablely by increase of polynomial fitting orders when the under-test wavefront is ideal spherical wavefront. By reconstructing sine wavefront, cosine wavefront, aspherical wavefront and normal wavefront which contains low order of spherical aberration, coma, astigmatism, field curvature and distortion aberrations, the accuracy of Zernike modal wavefront reconstruction and two-dimension insert modal wavefront reconstruction is compared. A more stable and accurate basic of modal wavefront reconstruction is obtained.

The effect of the atmospheric turbulence can deteriorate the performance of the free-space optical (FSO) communication system. A technique for using orthogonal frequency division multiplexing (OFDM) modulation in FSO is studied, the bit error rate (BER) performance of FSO-OFDM modulation system over Gamma-Gamma atmospheric turbulence is analyzed. Under different atmospheric turbulence intensity, the BER of OFDM modulation system is compared with on/off keying (OOK) modulation system. The simulation results show that OOK modulation system and OFDM modulation system are deteriorating with the strengthening of turbulence intensity, under different atmospheric turbulence intensity, the BER performance of 4QAM-OFDM modulation system is better than 16QAM-OFDM modulation system and OOK modulation system.

Aimed at the problem that the ominidirectional sea-wave spectrum of fractal sea-wave model could not satisfy the positive power law when spatial wave numbers is smaller than the fundamental wave number, a 2-D sea-wave model is proposed by combining statistical sea model and normalization band-limited Weierstrass-Mandelbrot fractal sea-wave model. Sea surfaces of statistical model, classical fractal model and the improved model are compared. Electromagnetic scattering coefficient of the improved model based on the Kirchhoff approximation is derived. The angular distributions of incoherent scattering intensity coefficient of statistical model, classical fractal model and improved model are compared, and incoherent scattering intensity coefficient of improved model is analyzed based on different frequency and wind direction in microwave band. Analytical results show that sea surface have both characters of large-scale turbulent waves and micro-scale capillary wave and the electromagnetic scattering of improved model can comply better with the practical situation of sea surface.

A new method is presented for atmospheric CO2 balloonsonde measurement. Based on Beer-Bouguer-Lambert law and non-dispersed infrared (NDIR) technique, an experimental device is designed and developed. A infrared LED is used to produce suitable light source, and infrared LED detectors and a proper electronic circuit designed are used to transform light intensity into electrical signals in the experimental device. Calibration method for CO2 measurement is also presented. A comparison experiment is carried out for continuous 24 h on ground with EC9820 analyzer. Result shows that measurement error ranges from -10×10-6 to 10×10-6, and standard deviation is 3.76×10-6, which basically satisfies the precision demand for atmospheric CO2 measurement. The feasibility of CO2 measurement has been validated.

The fluxes of heat, water and other trace gases are measured directly using eddy covariance method. For eddy covariance measurements, a new calibration-free open-path trace gas analyzer, based on tunable diode laser absorption spectroscopy (TDLAS), is developed and applied for trace gas fluxes in the atmospheric surface layer. By selecting different absorption lines, different trace gases are detected. Carbon diode absorption line (near 4990 cm-1) is taken as an example. The output bandwidth of the new gas analyzer is more than 10 Hz. A comparative experiment is conducted between a reliable commercial analyzer (Li-7500) using non-dispersive infrared (NDIR) gas sensor and our new trace gas analyzer. The collected data demonstrate an excellent qualitative agreement and show that the sensitivity of our gas sensor is about 5×10-7. It is indicated that the fast sampling and high sensitivity meet the requirements of the eddy covariance method. This TDLAS trace gas analyzer is a suitable technique for determining the fluxes of trace gases using eddy covariance method.

The Raman-Rayleigh-Mie lidar (RRML) system in the Nanjing Comprehensive Observation Base of China Meteorological Administration is introduced. In order to get accurate aerosol data, we use the lidar signal from Mie channel of the lidar system to measure the aerosol in the northern suburbs of Nanjing. The extinction profiles at different weather conditions (sunny and cloudy) are obtained. The variation of aerosol with time and wind direction is analyzed. The stratus base height and extinction structure are observed. According to experiments in real time, the aerosol loading changes with time in the windy case. The measurement results indicate that lidar can be finely used in dectecting aerosol. Tropospheric aerosol loading varies with wind direction due to the geographic location of Nanjing. The aerosol optical depth in the whole year of 2011 first increased and then decreased and the maximum value occurred in September. The extinction structure in stratus could be symmetric or asymmetric. Aerosol at the boundary layer diffuses downward, at the same time the altitude of boundary layer keeps stable and extinction of aerosol at low-altitude increases. In this process, the optical depth of aerosol from ground to boundary layer remains unchanged.

The theoretic expressions of loss in different scattering orders are analysed by imitating random migrations of photons in free space. The predicted path loss under different elevation angles are presented and compared with relevant literature to validate it. It can be concluded from the simulation that under specific preferences, high orders of scattering (higher than four orders) contribute little to the total energy of received optical signal (at least 10 orders of magnitude smaller), and thus the effects caused by the 4th or higher orders of scattering can be neglected.

Based on the Mie theory, the light scattering properties (single scattering albedo, asymmetry parameters, and single scattering phase matrix) in the visible regions of clouds consisting of pure water, pure ice spheres and concentric water-ice spheres are computed respectively. The reflection matrixes of the three types of clouds are evaluated with the adding-doubling method by solving the radiative transfer equation. The reflection characteristics of different light wavelengths are compared. The numerical results show that the polarization degree of reflected light is more sensitive to the particle microphysics characteristics than the intensity of reflected light.

An algorithm for retrieving polluted coastal aerosol optical properties based on moderate resolution imaging spectrometer (MODIS) data is proposed. New aerosol modes are created based on the characteristics of coastal aerosols; the limitation of computing apparent reflectance in MODIS algorithm is removed; and by selecting infrared spectroscopy bands, water leaving radiance from case II water is reduced. Aerosol robotic network (AERONET) sites data are used to test the proposed algorithm, and the results show that more than two-thirds retrievals lie within the expected error bars. The retrieval meets the requirements of the ocean retrieval accuracy.

In design of an adaptive optics system, a critical consideration is the bandwidth requirements for turbulence-induced tilt compensation, Tyler frequency. A method to evaluate the Tyler frequency is proposed according to the measured total tilt power spectrum. First, the power spectrum of the horizontal turbulence is measured through a Shark-Hartmann wavefront sensor. Then, the Tyler frequency is determined by which the tilt cut-off residual error of a diffraction angle is applied. The result illustrates that the tilt power spectrum is proportional to f-2 (f is temporal frequency) at high frequencies. At last, the circadian variation of Tyler frequency is acquired. It illustrates the important fact that, at night and early morning, the Tyler frequency of horizontal turbulence changes slowly, generally less than 4Hz in the turbulence condition, but it is volatile during the day, the largest up to about 20 Hz in Changchun. Therefore, the temporal bandwidth of the tip-tilt, in which the adaptive optics systems are used for the horizontal turbulence correction under such turbulence condition, must exceed 20 Hz.

The transmitting beams are usually approximated as plane wave or spherical wave in free space optical communication (FSO) systems. But the actual beam is a Gaussian beam, and there are many differences when we study the performance of FSO system with the approximation model. By using the methods of theoretical analysis and simulation, without considering the impact of the inner and outer scales of turbulence, we analyze the difference of aperture averaging effect among different transmitting beams. The differences of bit-error rate (BER) performance are then analyzed. The results show that Gaussian wave has apparent impact on the improvement of BER performance by aperture averaging, and saturation is reached firstly, followed by spherical wave. Plane wave is relatively gentle.

A high-speed data acquisition and processing system with integrated transceivers is designed to measure and monitor the wind fields at real time,which plays an important role in the multi-laser beam displacement measurement of wind field system. It can also realize the real-time extraction of low signal noise ratio (SNR) signals,which transforms rapidly in a wide dynamic range,spatial filtering,precision delay and accurate gate control technology. This system is mainly composed of YAG pulsed laser,avalanche photo diode (APD) detector,cascaded gain amplifiers,analog-to-digital conversion circuitry,field programmable gate array(FPGA) processing chip and its peripheral circuits,single-chip control systems and data transmission circuit. The experimental verification is also carried out,and the results show that multi-beam displacement measuring system can effectively detect the backscatter signals in various distances,by which we can calculate the wind speed and get the wind direction from data analysis.

A group of reference calibration coefficients for China-Brazil earth resource satellite(CBERS)-02′s CCD data were attained by cross calibration method using LANDSAT-5′s TM data. A method based on meteorological information and ATCOR3 was used in the atmospheric correction of CBERS-02′s CCD four bands. The definition of image and normalized difference vegetation index (NDVI) before correction were compared with them after correction. The result shows that after atmospheric correction the image contrast is enhanced,the mean of NDVI is obviously improved and the difference of NDVI between vegetation and nonvegetation is increased. When the underlying surface is rugged terrain,the corner angle of mountain is distinct,the profile is clear and the original shape is recovered,which benefits the extract of remote sensing information.

A method for red tide detecting and monitoring by the airborne blue-green lidar is proposed based on analyzing the blue-green optical properties of the seawater. The blue-green laser can enter the seawater deeply, and the information of red tide in the deep seawater can be detected by using the blue-green lidar. By detecting the blue-green light scattering signal under the seawater, the information of red tide density can be gained. A red tide density detecting model based on airborne blue-green lidar is established through analyzing the absorbing and scattering characteristics of the red tide. By emulating and computing, it is proved that the method can detect and monitor the density of the ocean red tide effectively, and therefore it can also predict the occurrence of red tide.

Spectra interpolation is used to analyze differential optical absorption spectroscopy (DOAS) spectra, which can greatly decrease the absorption elimination error of the high concentration species and achieve accurate measurements of trace compounds including NO3, glyoxal ((CHO)2 ), mono-aromatic hydrocarbons (MAHC), et al by DOAS. The changes of high pressure Xe arc lamp (called Xe lamp for short) structure, resulting from the changes of temperature and pressure, are simulated accurately, which enables the analysis of indicator of atmospheric photochemical reaction -(CHO)2 without the interference of Xe lamp structure (more than one hundred times higher compared with (CHO)2) near 450 nm. The mass dependent absorption structure of H2O is simulated and the accurate measurement of the “cleaner” of nocturnal atmospheric pollutant -NO3 is achieved without the interference of nonlinear absorption of H2O near 662 nm and 623 nm. The mass dependent absorption of O2 and the temperature dependent absorption of O3 are simulated, which enables the accurate measurement of MAHC in the range of 250～285 nm free of the effect of much higher absorption of O2 and O3.

We report a new type of ultraviolet(UV) CCD optical multi-channel analyzer and its application for detecting solar ultraviolet irradiance spectrum. Primary analysis on detection results of solar UV irradiance spectrum indicates that in the morning and in the afternoon the irradiance of solar UV is smaller than that at noon, and reverse correlates to the change of solar zenith angle (SZA). Radiation of different bands are different: long-wave radiation is generally higher than short wave radiation. Solar UV radiation spectral intensity is bated by the effects of clouds, and the attenuation depends on the wavelength and decreases with decreasing wavelength. UV-CCD optical multi-channel analyzer can be used to monitor the total amount of solar UV radiation, and to analyze the amount of radiation at all wavelengths and the relative charges of radiation at different wavelengths in different atmospheric conditions.