Atomic force microscope(AFM) is one of the main instruments in the microscale and nanoscale measurement area. Since the AFM tip can′t be infinitely sharp, the shape of the tip is included in AFM image. This is a big source of image distortion. To obtain the shape and dimensions of tip is an effective method to remove the "tip effect" and improve the accuracy of measurement images. In this study, tip characterizers with high intra-sample uniformity were fabricated by utilizing the Si/SiO2 multilayer gratings technology, and critical dimension(CD) structures with a nominal CD of 20 nm had been fabricated to calibrate the tip. The calibration results showed that the selected AFM tip(Rectangular Front Etched Silicon Probe, RFESP) became blunt after scanning, together with the front side angle(15°) and back side angle (25°) increased to 36° and 45°, respectively. Therefore, the tip characterizers formed by the Si/SiO2 multilayer CD structures can be used to quickly obtain the side angle information, which is an effective method to complete the fast check and estimations of tip shapes during the AFM scanning. The investigation of AFM tip characterization based on multilayer gratings are meaningful for the promotion of accuracy in AFM measurement images.

In order to obtain accurate nano-film parameters in the ellipsometry measurement process, a hybrid optimization algorithm for nano-film parameter data processing was proposed. An Improved Particle Swarm Optimization-Neural Network(IPSO-NN) hybrid optimization algorithm has been proposed, based on the features of artificial neural network algorithm back propagation and particle swarm algorithm for fast optimization. This algorithm has the ability to jump out of the local optimal solution quickly with fewer iterations, so as to quickly find the optimal solution of ellipsometric equation. The algorithm was used to calculate the film parameters of silicon dioxide nano-film thickness standard template with a strandard value of 26.7±0.4 nm in this paper. The results show that the relative error of the film thickness calculation by IPSO-NN hybrid optimization algorithm is less than 2%, and the refractive index error is less than 0.1. At the same time, this paper compares the traditional particle swarm algorithm with the IPSO-NN algorithm through experiments, and verifies that the IPSO-NN algorithm can optimize the number of iterations effectively and the process of finding the optimal solution. This algorithm can achieve rapid convergence and improve the calculation efficiency when calculating the thin film parameters.

In order to analyze the performance of the laser emission system, it was necessary to measure the spatial-temporal distribution of the absolute power density of the laser spot. The detector array target was one of the effective methods. To achieve quantitative analysis, the detector array target needed to be calibrated. The number of detector array target units was large, and the calibration was difficult. It was very important to design an effective calibration system. This paper designed a new calibration system, which adopted the point-by-point scanning method. This way had the characteristics of wide applicability, low cost and high precision. In order to test the system, taking a project as an example, the measurement uncertainty of the calibration system was tested and analyzed. The results show that the measurement uncertainty in the visible light band is 2.99%, and the measurement uncertainty in the near-infrared band is 3.62%. The measurement uncertainty in the mid-infrared band is 6.17%. This calibration system was an effective way for target calibration of detector array, it was worth learning.

Based on spectral interference technique, a method for simultaneously measuring the thickness and refractive index of a glass was proposed. This method used the Michelson optical path to solve the interference signal received by the spectrometer through a Fourier transform algorithm to obtain the modulation period of the spectral interference fringe. The modulation period was determined according to the optical path difference formed between the measuring arm and the reference arm before and after the glass sample to be tested was placed in the measuring arm, and the geometric thickness and refractive index of the glass sample can be obtained. The method did not need mechanical scanning delay line and adopted the improved phase extraction algorithm in the Fourier domain, which improved the anti-interference ability of the measurement system and the detection speed was fast. The experimental results show that the thickness measurement accuracy of the glass sample is better than ±1 ?滋m, and the refractive index measurement accuracy is ±5×10-4.

In order to meet the requirement of precision image stabilization system for ground-based large aperture telescopes, the control method of large aperture fast steering mirror(FSM） was studied. For the sake of solving the difficulty of system identification caused by motion decoupling of three actuator driven FSM, the transfer function model of FSM was established by combining analytical method and system identification method. According to the model, the PID controller and the model predictive controller (MPC) were designed, and the performance of the two controllers were compared by simulation and experiment. The simulation results show that the recovery speed of the MPC controller was 45 times faster than that of the PID controller after step disturbance. Under 50 Hz sinusoidal signals, due to the large inertia of FSM, the PID controller had a serious time delay, while the MPC controller could track steadily with an error of 1.224×10-6 ″. In terms of noise suppression, under the random signal with 10% amplitude noise added in real time, the noise suppression performance of the MPC controller was 13.3 times better than that of the PID controller. The experimental results show that 50 Hz sinusoidal signal could be tracked stably by the MPC controller with an error of 0.430″. The tracking accuracy of the MPC controller was 3.212 times higher than that of the PID controller. The results show that the fast steering mirror with MPC controller could satisfy the requirements of high bandwidth and high precision of the fast steering mirror.

In order to satisfy the stringent requirement for high surface shape accuracy and thermal stability of large-aperture mirrors in the complex space environment, a lightweight design for a Φ660 mm-diameter mirror was carried out. A method for creating the initial structure of the mirror using the classical theoretical formula, combining sensitivity analysis and parameter optimization for comprehensive design was proposed. Firstly, the parametric model was established, the influence law of the structure parameters of the mirror on the surface shape change was studied, and then iterations for the structural parameters with high sensitivity to the mirror surface RMS value were optimized through sensitivity analysis. Compared with the traditional mirror design model, this method reduced the optimization design space, saved computational cost and time, could globally optimize in the design space, and converged quickly to the optimal value. The mass of optimized mirror was 13.6 kg and the lightweight rate of the mirror reached 78.4%. The PV value of mirror surface accuracy was less than ?姿/10 and RMS value was less ?姿/40(λ=632.8 nm) under gravity load. The first-order frequency 121 Hz of the mirror assembly met the dynamic stiffness requirements of the mirror. Finally, based on the optimized results, the optimal mirror was put into production.

In the design of mirror and its supporting structure in cryogenic environment, the surface accuracy under the temperature variation is an important factor affecting the performance of the space mirror. The surface shape RMS under the temperature change was taken as the performance index, and the surface shape variation of the space mirror was compared and studied based on the different supporting structures of the mirror manufactured by silicon carbide and the collocation forms of different materials. Firstly, the following two conditions of back support and lateral support were simulated and analyzed in cryogenic environment: (a) the mirror and the supporting structure was made of silicon carbide; (b) the mirror was made of silicon carbide and the supporting structure was made of other materials. Simulation analysis shows that the back support structure can obtain a better surface shape under condition (a), and the lateral support structure can obtain a better surface shape under condition (b). Then, the influence of the side supporting structure on the surface accuracy under different material matching conditions was studied. The relationship among the RMS and the CTE(coefficient of linear thermal expansion) of mirror material, the CTE of supporting structure materials, the absolute value of the difference between the CTE of mirror material land the CTE of supporting structure materials was analyzed using multivariate linear regression method. The analysis result shows that the absolute value of the difference between the CTE of mirror material and the CTE of supporting structure materials has greater influence on the RMS. The research results and ideas provide reference for the design of cryogenic optical mirror and its supporting structure in the future.

According to the theory of diffractive optics, the imaging quality influence mechanism of the diffraction effect of the field stop for the field of view selection and side lobes filtering in the pupil function modulated modulation telescope telescopic super-resolution imaging was analyzed, and the compensating principle and method were given. The tiny hole field stop and the four-ring step phase filter were placed in the first image plane and the exit pupil respectively. Theoretical analysis and simulation show that the smaller the field stop aperture, the wider the main lobe of the spot on the final image surface, (even the super-resolution effect will disappear), and the higher the ratio of the peak intensity of the side lobe to the peak intensity of the main lobe. The polynomial fitting of the amplitude and phase fields at the exit pupil and the solving of the modified complex-amplitude pupil filter design parameters can effectively suppress the diffraction effect of the field stop, which leads to a good super-resolution imaging. Moreover, the super-resolution imaging and the pupil effect compensation were combined into one, which did not increase the complexity of the system optical path. The actual experiment was carried out to verify the availability of the above design method. The above research results can be used as a basis for the design of super-resolution imaging system applied in the astronomical observation and space exploration.

In order to meet the space application requirements of the low-level infrared detector assembly in the high reliability field, environmental reliability tests, such as temperature cycling test, mechanical test and high temperature aging test had been carried out on the space-borne infrared detector assembly. Meanwhile, the relative spectral responsivity of the infrared detector assembly was tested based on double integral ball uniform illumination system before and after environmental reliability tests. By comparing differences of the relative spectral responsivity of the infrared detector assembly before and after environmental reliability tests, the environmental adaptability of the infrared detector assembly was analyzed, while the quality defects and other potential defects of the infrared detector assembly were revealed with the early eliminated failures. Then, the detectors with optimal performance were extracted from the participating infrared detector assembly, which were used in the space-borne polarization scanner for atmospheric polarization detection. The test results show that the tested infrared detector assembly are in good stability and reliability before and after environmental reliability tests, which can meet the aerospace load application requirements.

Serious geometric distortion in IR linear scanning image will affect the tactical efficiency of patrol missiles, which is generated from high speed maneuvering, large filed of view(LFOV), pendulum scanning of the missile-borne image. The strict imaging model was constructed by converting the pixel serial numbers of infrared image into certain map projection coordinates of the surfacial scene, which was composed of four equations. Image plane coordinates equation was built by pixel parameters of infrared chip surface. Image spacial coordinates equation was built to transform image plane coordinates into earth-centered earth-fixed(ECEF) coordinates. The surfacial object coordinates equation was built in ECEF system by collinear equation and the earth surface model. The last map coordinates equation was built by certain map projection model form the object ECEF coordinates. The static simulation of geometric distortion was implemented in Matlab to ascertain the effect of model parameters such as navigation height, pendulum angle, the earth model and so on. The results could be used as the basis for the engeering optimization of geometric distortion cerrection algorithm.

In order to identify anti-jamming performance of the infrared missile, the infrared countermeasure environment need to be quantitatively evaluated. However, most of the current models analyzed the missile′s anti-jamming performance from the terminal miss distance, couldn′t reflect the response of each module of the missile in the process of being interfered. Therefore, based on the missile seeker system and the guidance control system in the process of jamming, a quantitative modeling method of infrared countermeasure environment was proposed. Firstly, the infrared countermeasure elements model was constructed from the scene composition and physical characteristics. Secondly, based on the influence of the countermeasure elements on the image recognition and the guidance control system, the indicators of similarity, masking degree, jamming time, target maneuver and entry angle were proposed. Finally, by using parallel relation model, geometric mean synthesis model and weighted sum model, the total environmental complexity quantification model was established based on the above indicators. Simulation experiments show that the probability of the missile hit ratio error within ±6% predicted by this model is 95% in typical countermeasure scenarios.

The air target has the following characteristics: high-speed maneuver, strategic deep penetration and long-range precision strike. Building wide-area, high-efficiency, accurate detection and continuous monitoring for air targets has become a new challenge for air target detection. In view of the optical detection requirements of air targets, a radiation characteristic model of aircraft plume was established under the combined effect of complex environmental factors. An accurate prediction model of the full chain including aircraft plume-sea/cloud background-environmental atmosphere-optical system-imaging detector was formed. The infrared multi-spectral self-radiation of the aircraft plume was derived based on the measured data. At the same time, the FY-2G remote sensing data was used to invert the sea surface temperature and cloud top temperature distribution in a certain sea area of the South China Sea, and the background radiation model of sea/cloud background was established. On this basis, the effects of background radiation, atmospheric path radiation and atmospheric attenuation on the spectral radiation of the aircraft plume were considered. A model for the upstream spectral radiation of the target at the entrance of the optical system was established. Combined with the diffraction effect of optical imaging system, the detectability of the infrared imaging system in the geostationary orbit under different spectral segments and cloud types was discussed. Research shows that detection efficiency is better in the atmospheric shielding band than in the wide band, and reasonable detection band selection in different backgrounds is conducive to efficient detection of targets.

Based on the compact and efficient optically pumped terahertz laser(OPTL) technology, an optically pumped terahertz fiber laser(OPTFL) based on a negative curvature hollow core fiber was designed. This OPTFL used a hollow-core fiber with polymethylpentene(PMP) material as operation gas chamber and was filled with methanol gas and pumped by 9P(36) continuous-wave(CW) CO2 laser. Based on rate equations and the transmission theory in hollow core fiber, factors affecting the output characteristics of OPTFL were analyzed. By investigating inner microstructure of hollow-core fiber, a negative curvature hollow-core fiber for efficiently transmitting terahertz waves was proposed. Considering the designed negative curvature hollow-core fiber, the feasibility of long cavity OPTFL was analyzed. Theoretical calculations showed that by appropriately increasing the cavity length of the proposed OPTFL, the terahertz output power was expected to reach the order of 100 milliwatts with optimal operating conditions. The results provide a new method for the OPTFL with high power and high performance.

In the field of quantum detection, one of the key tasks is to measure the unknown quantum state to obtain quantum state information. By applying the quantum circuit composed of quantum gates in quantum computing to the field of quantum detection, a measurement scheme for realizing the unknown quantum state of single photons was proposed. Utilizing the superposition of quantum computing, entanglement, error correctability, and the integratability of quantum lines, it was possible to make detection more efficient and simplify the experimental system of detection. Using the new detection method proposed in this paper, the scheme was simulated by simulation. Based on the theoretical calculation and simulation results of the scheme, the following conclusions was obtained: by selecting appropriate measurement times under different parameters such as SNR, the quantum line-based scheme can obtain more accurate measurement results.

The solar background radiation seriously reduces the signal to noise ratio of the lidar detection, and affects the detection height and accuracy of lidar system during the daytime. In order to obtain the relevant parameters of the middle atmosphere all time, an ultra-narrow band filter used on all time detection was developed in 355 nm wavelength of laser. First of all, an ultra-narrow band filter was designed on all time observation with the character that the band of a single pass rate curve of FPI was very narrow. Then, the approximate transmission function of the ultra-narrow band filter was infered, the performance evaluation function was defined, and the design method was given. With the performance evaluation function, the main parameters of the ultra-narrow band filter were optimized and the parameters of each optical component were given. The signal-to-noise ratio of the ultra-narrow band filter was increased 50 times than the 0.15 nm interference filter. Finally, the transmission rate curves of each optical component and cascaded etalon system were calibrated through experiment. The fitting curve shows good consistency with the experimental data.

An approach to generate linear frequency modulation laser source based on an optical phase modulator and a tunable optical filter was proposed. A narrow linewidth fiber laser seed source was modulated by an optical phase modulator, whose driven ratio frequency (RF) signal was generated by the microwave linear frequency modulation signal with a fundamental frequency, and thus a series of wideband linear frequency modulation laser signals were generated. A tunable optical filter was used to select the desired linear frequency modulation optical sideband and suppress the others modulation sidebands. The experimental results show that when the optical filter retains the positive second order modulation sideband, a linear frequency modulation laser signal with a tuning range of 2 GHz and tuning rate of 6 THz/s is obtained. The instantaneous linewidth of the linear frequency modulation laser signal is 3.2 kHz in 1 ms observation time. The system is simple in structure and easy to implement. This technique has important significance for the applications such as frequency modulated continuous wave laser radar and coherent spectroscopy.

The spectrally-resolved scanning calibration is an important technique to satisfy the high accuracy spectral radiometric calibration of remote sensors. The calibration facility based on supercontinuum laser and monochromator(SCM) is a new choice to realize spectrally-resolved scanning calibration of remote sensors. To verify the system-level calibration capability of the SCM, the spectral radiance responsivity of the silicon radiometer and filter radiometer were measured by using the calibration facility based on the supercontinuum laser monochromator and the tunable laser, respectively. The experimental results showed that the maximum deviation of the calibration results for silicon radiometer between supercontinuum laser monochromator and tunable laser was 0.6% within the validated band. And the maximum deviation of in-band absolute spectral responsivity calibration results of channel filter radiometer was better than 0.4%, and the maximum deviation of in-band integral responsivity was about 0.1%. The research in this paper verifies that the supercontinuum laser monochromator calibration facility has good system-level calibration capability, can obtain high calibration accuracy. It has important application prospects in the calibration of absolute spectral responsivity of remote sensors.

The peak-picking method which is commonly used in Gm-APD laser radar 3D reconstruction always gets the wrong target position when there is an abnormal peak, and the reconstructed image has low signal-to-noise ratio and target missing because the threshold can only be integer. To solve these problems, a weighted Gaussian-like matched filtering algorithm was proposed. Fitting the echo firing histogram and normalizing can get the weight. Then the weighted window smoothing histogram was used and the peak position was selected again for reconstruction. According to the Poisson distribution of Gm-APD, the detection probability and false-alarm probability expression of the algorithm can be obtained, then compared with the peak method. The result show that the weighted Gaussian-like matched filter algorithm is better for the target in the middle of the gate. The theoretical derivation results are verified by Monte Carlo simulation. At last, by using the real experimental data and reconstructing data with two kinds of algorithms, the consequence shows that the weighted Gaussian-like matched filtering algorithm has a significant improvement on the restoration subjective and objective compared with the peak method. The results show that this algorithm has a good practical application prospect in dealing with low SNR and real-time 3D reconstruction.

Graphene has excellent physical and chemical properties, and has become a research hotspot in the fields of MEMS devices, photoelectric detection materials, flexible display screens, new energy batteries and composite materials. At present, the preparation of large area graphene mainly depends on chemical vapor deposition (CVD), but the crystal quality of graphene growth directly affects the electrochemical characteristics and practical applications, so a fast and accurate characterization method is needed. Raman spectra of graphene grown by CVD were measured by backscattering polarized laser scattering device. Angular resolved polarization Raman spectra of graphene on 300 nm SiO2/Si substrates were analyzed. It was found that the polarization characteristics of graphene grown in single layer were consistent with those of mechanically stripped graphene. The polarization response of G peak was more distinct with the increase of the number of layers, showing obvious elliptical characteristics. In graphene samples with different layers, the defects in the samples showed obvious D peaks and polarization responses due to the increase of layers. The polarization states of the 2D peaks were not significantly different in different samples and were not affected by the number of layers. Polarization Raman measurements show that the defects and polycrystalline properties of CVD growth are positively correlated with the number of graphene layers.

In order to analyze the amplitude and frequency characteristics of the 129Xe spin oscillator in the nuclear magnetic resonance gyroscope (NMRG), a corresponding theoretical model was established. The density matrix and the classical electromagnetic theory were utilized to describe the nuclear spin ensemble and the feedback system, respectively. An oscillation equation with self-consistency condition was obtained. Furthermore, the oscillation equation was simplified and expanded to self-consistency equations with rotating-wave and slow-varying approximations, which described the amplitude and frequency of the oscillator simultaneously. Based on the semiclassical model, the influence of a band-pass filter on the amplitude and frequency of the spin oscillator was investigated. The simulation results indicate that the typical frequency shift caused by unsuitable feedback loop may reach the magnitude of sub-micro Hz. Proposed model offers the potential to improve the performance of NMRG based on spin oscillators.

A simple and practical method for MMS laser scanner calibration with hybrid regular geometric surfaces was proposed. The method utilized the plane and cylindrical objects which were ubiquitous in the real environment, and combined the geometric characteristics of the plane and cylindrical surface to constrain the laser point in a rigorous mathematical equation, and non-linear least square solution to determine the relative position and attitude parameters of the scanner relative to the MMS positioning and attitude measuring device POS accurately. The method did not need to establish a special calibration site. The experimental results show that the hybrid regular geometric surface combined constraint calibration method is more accurate than the method using only plane objects, reaching 0.006 m. After the same vehicle platform and two different laser scanner systems are calibrated, the point cloud superposition effect is better. The method is accurate, simple, fast, inexpensive, efficient and practical. The measured accuracy meets the requirements of large-scale production.

As an important instrument for optical observation in the water, lidar is able to efficiently obtain vertical profiles of ocean optical properties. Based on the airborne lidar model of Gordon (1982) for measuring water optical property, the processes of shipborne lidar radiative transfer and distribution of underwater light field were investigated using Monte Carlo simulation. In particular, taking into consideration receiving FOV and telescope aperture, a shipborne oceanographic lidar simulator was developed. After lidar radiative transfer was equivalent to solar radiative transfer, the simulator was validated with commonly used HydroLight which showed good coincidence. On this basis, using simulated lidar return signal, the relationships between lidar extinction coefficient α and ocean optical properties were analyzed for different observation modes and typical water bodies. The results of shipborne lidar show that with narrow receiving field of view(FOV), lidar extinction coefficient α is close to beam attenuation coefficient c, and with large receiving FOV, lidar extinction coefficient α gradually approaches to diffuse attenuation coefficient of downwelling irradiance Kd. The extinction coefficient α measured with shipborne lidar approaches to Kd slower than the airborne situation. The results of stratified water show that the α values measured in lower layer water shift towards the α values in upper layer water. The results provide the further understanding for researching the relationship between parameters measured by oceanographic lidar and ocean optical properties.

Ocean is an important part of the earth′s ecological environment. Exploration and exploitation of marine resources may easily cause serious damage to ocean, such as large-scale oil spill, pollution and red tide caused by oil and gas exploitation. Hyperspectral imaging technology can obtain both image information and spectral information at the same time, and has important applications in marine in-situ detection. In this paper, some recent works about hyperspectral imagers are reviewed, including a small-scale hyperspectral imager combined with fluorescence technology for the classification of oil spills and the estimation of oil film thickness, a multi-mode hyperspectral marine in-situ detection system (in three modes: common reflection or transmission imaging, telescopic imaging and microscopic imaging) for hyperspectral detection of different algae and spores of some fish infectious disease carriers. Hyperspectral technology combined with lidar technology has great potential in monitoring oil spill, red tide and other marine pollutants. An inelastic hyperspectral Scheimpflug lidar system and a ligh-sheet Scheimpflug lidar system are also reviewed. The former is for the type identification of oil spills through the fluorescence spectrum of oil spills, and the latter is for the detection of the 3D shapes of some manikin, shells and corals with the refraction correction at the air-water interface.

Compared with traditional underwater cameras, the detection distance of underwater range- gated imaging can be increased by 2-3 times. Furthermore, based on this technology, fast high-resolution 3D imaging can be achieved. It has great potentials in underwater target detection and recognition, automatic navigation, marine scientific research and natural resources exploration. Although range-gated imaging can suppress the backscattering noise by space slicing, and achieve higher quality images, the backscattering noise of the sampling water volume still exists in gated images, resulting in low image signal-to-noise ratio and contrast, especially for distant targets or low reflectance targets. This paper systematically introduced author′s research of deblurring methods for 2D and 3D range-gated imaging. In 2D imaging, two methods were proposed: the first was an algorithm of self-adaptive double-plateau histogram equalization to improve image contrast and better meet human vision; the second was to use a water-noise-reference denoising algorithm to improve the signal-to-noise ratio of target gated images. In 3D imaging, there were also two methods proposed: one was to use the water-noise-reference denoising algorithm for 3D reconstruction, and the other was to use the threshold-dependent joint bilateral filter algorithm for enhancing 3D images. The four proposed methods can be used independently or in combination for denoising enhancement of underwater range gated imaging.

Ocean optical systems have played an increasingly important role in ocean exploration, development and monitoring. Underwater wireless optical communication and underwater lidar are two types of ocean optical systems that are rapidly developing and have good application prospects. Underwater wireless optical communication is an ideal communication option for short and medium range applications due to high speed and low latency. Underwater lidar is also a highly precise and efficient observation method in applications like deriving geographic information and target detection. However, the complex optical characteristics of seawater channels have brought challenges to the further improvement of the performance of ocean optical systems. In seawater channels, not only strong absorption and scattering, but also dynamic interference factors such as turbulence and bubbles exist in the channel. In order to deal with these challenges, on one hand, signal to noise ratio can be increased with temporal or spatial methods. On the other hand, the conversion between temporal and spatial domains is beneficial to achieving better system performance. This article reviews solutions above and the development trend of ocean optical systems is pointed out.

Blue-green laser has broad application prospects in non-acoustic detection of underwater targets. However, the existing detection models have not considered the problem of matching the detection probability with the self-guided system. A target detection model of underwater laser scanning detecting system was established based on undershoot distance to match the guiding precision. The simulation results shows that an increasing undershoot distance needs an increasing emit angle to get high detection probability at a certain emit frequency, which however leads to a decreasing acting time for the following system. In addition, an increasing undershoot distance needs an increasing emit frequency and a decreasing step angle to avoid missing the target. Finally, the simulation provides an optimal range for undershoot distance and system parameter. The model and the simulation results provide theoretic basis for the matching up design of guiding system and detecting system.

Underwater spectral imaging technology plays an important role in underwater object recognition and ocean ecological monitoring. An underwater spectral imaging system using liquid crystal tunable filter (LCTF) was designed based on the actual engineering environment. The system obtained spectral information by using LCTF as a filter structure. Under the illumination of a wide-spectrum LED, a pool experiment was performed to obtain 31 channel spectral images of the target between 400 and 700 nm. The spectral information of objects with similar colors under water was discussed and analyzed. The results show that the system is helpful for underwater target recognition and classification. In-situ observation of corals in the sea trial successfully obtained underwater spectral images of coral reefs. The system is expected to be applied to ocean remote sensing, ocean ecological environment monitoring and other fields.

A combination of formula derivation and simulation optimization was used to design a LiDAR optical-mechanical system for measuring water depth. The light source of this system used 532 nm and 1 064 nm dual-frequency lasers. Three receiving channels of 532, 647 and 1 064 nm were designed. The planned flight height was 140-500 m, the variable scanning angle is 9°-15°, the divergence angle was less than 0.5 mrad, and the surface point density range was about 0.687-4.170 points/m2. In this paper, Raman band was designed as a water depth measurement band to improve the measurement effect in shallow water. The variable scanning angle was used to realize the functions of variable resolution under a fixable width and the consideration of high precision and large field of view to adapt to different application scenarios.=

Oceanic lidar is a vital remote sensing device for detecting the upper ocean and constructing the 3-D ocean observation network. In this paper, the experimental data of lidar were compared with Monte Carlo(MC) simulation, analytical model and in situ data to find their matched-degree. Compared with experimental lidar signals, the MC simulation and analytical model have high agreement (R2>0.97). The normal lidar equation approximately adopting the in situ diffuse attenuation coefficient (Kd) also has good consistency (R2>0.92). The retrieved lidar attenuation coefficients show similar results. The MC simulation and the analytical model have better consistency. The results show that the experimental results of oceanic lidar match well with the simulation results of MC and analytical model.

Underwater visible light communication (UVLC) is an attractive solution to achieve high-speed and large-data transmission but challenging due to the impairments induced by absorption, scattering and turbulence. To combat effects of multipath and fading for the UVLC system over turbulence channels, optical orthogonal frequency division multiplexing (O-OFDM) schemes with the transceiver spatial diversity were proposed, which employed equal gain combining (EGC) at the receiver side. Underwater path loss was calculated by a generalized Lambertian formula, and the fading induced by weak turbulence was modelled as a lognormal-distribution random variable. Based on the channel model and Monte Carlo (MC) simulation, the bit error ratio (BER) performance for quadrature-amplitude modulation (QAM) asymmetrically clipped optical OFDM (ACO-OFDM) and DC-biased optical OFDM (DCO-OFDM) systems in the channel with and without turbulence was evaluated. Furthermore, the diversity gain was estimated for different diversity orders and scintillation indexes. The results demonstrate that the diversity scheme with EGC is an effective measure to reduce the effect of turbulence and could be useful for designing, predicting, and evaluating the performance of O-OFDM UVLC system in a weak oceanic turbulence condition.

In this paper, a spaceborne oceanic lidar simulation system used semianalytic Monte Carlo method was developed. The system can simulate the lidar returns of the atmosphere and the ocean with different optical properties through entering the parameters of the lidar system and the environmental parameters. At the same time, a user-friendly software interface for users was designed to operate input parameters and observe the output results intuitively. A variety of simulations was done, such as different types of water and different scattering phase functions. The simulation results were highly consistent with the theoretical lidar equations. The system was important to the research on the detection mechanism of spaceborne oceanic lidars.

UV-Vis （Ultraviolet and visible） spectrometry was used to measure the absorbance of seawater with different concentrations relative to pure water. In order to meet the requirements for high-precision detection of seawater absorbance, the inherent background signal of the instrument and the difference between the sample containers were used to detect the absorbance of seawater where the error was included in the research category, and the experimental method was further optimized. The subtraction method was used to filter out the interference of the background signal. At the same time, the repeatability of the cuvette empty cup with respect to air and the cuvette with respect to air were verified. The difference in absorbance, and the error caused by the difference between cuvettes was filtered by the method of subtraction, and a certain characteristic wavelength was selected to observe its absorbance data relative to pure water, which verified the use of optimized experimental detection. The method finally achieves the purpose of measuring the absorbance of seawater with high accuracy (＜0.000 5 AU). It was of considerable importance for detection of various substances in highly transparent water.

A system for measuring the volume scattering function of water with particles was built, helping the laser and the detector to avoid the shading of each other that causes the reduce of detection angle. A set of double-periscopic optical system was used to separate the detection plane of scattering plane from laser exiting plane, thus the shelter of the laser source was minimized. What′s more, as the transmission light was exported from the system, the scattering light of water container was avoided so that the precision of backscatter measurement was promoted. The prism for exporting underwater light was designed according to the manufacturing techniques and by which the scattering measurement equipment was designed to measure the scattering light ranges from 3° to 178°. Next, according to the structure of the system and the principle of optical transmission in water, data rectifying methods was designed to rectify the deviation of measurement optical distances and light absorption. The rectified results were finally compared with simulated results of Mie scattering, the main source of deviation was analyzed and the improvement scheme of the system was proposed.

For the problems of image quality degradation in underwater scene target detection, an algorithm which combined the improved dark channel with MSR was proposed, which could adaptively compute water attenuation coefficient and effectively realize the recovery of underwater target. Through the built-in underwater imaging measurement device, the detection image of the underwater simulated environment with the aid of imaging system was obtained, the underwater detection image was processed step by step according to the algorithm flow chart, and an image for the effective recovery of underwater target radiation information was obtained. In order to objectively evaluate the algorithm effect, contrast, average gradient and information entropy were adopted as quantification to evaluate indexes factors. A quantitative comparison study between this algorithm and the conventional three algorithms was performed. The result show that the improved algorithm to deal with the results is better than the selected compared algorithms under all the quantitative evaluation indexes factors. The research results provide a basic theoretical exploration method for the underwater target detection, as well as have certain guiding significance for the implementation of underwater target detection.

The impact of Gamma Gamma strong oceanic turbulence and pointing error on the average bit error rate(BER) and outage probability of a heterodyne differential phase-shift keying(DPSK) underwater wireless optical communication(UWOC) system with an aperture receiver was investigated. The optical intensity fluctuation due to the combined effects of oceanic turbulence and pointing error was derived. The close-form expressions for the average BER and outage probability were derived. Then the average BER performance and the outage probability performance versus signal to noise ratio(SNR) of the considered UWOC system were investigated with different point errors, source beam widths, receiver aperture sizes and oceanic turbulence parameters. The results indicate that the larger the aiming error is, the worse the system performance is, under the same beam width and channel environment. Choosing a larger radio of source beam width to aperture radius or a bigger aperture receiver can help to improve the system performance. In addition, the system shows a better performance over the strong oceanic turbulence with a smaller ratio of temperature to salinity contributions to the refractive index spectrum ?棕 and the rate of dissipation of mean-squared temperature ?字T or a larger rate of dissipation of kinetic energy per unit mass of fluid ?着 and the kinetic viscosity u. This work will provide reference for the construction and performance estimation of UWOC system on strong oceanic turbulence when taking pointing error into consideration.

Pulsar navigation is a new type of autonomous navigation. In order to improve its accuracy and real-time, a method of pulsar time of arrival(TOA) estimation combining wavelet transform and compressed sensing was proposed. This method constructed a multi-level redundancy dictionary using wavelet transform for the standard algorithm complexity of this method was lower than the traditional TOA estimation method, and the real-time performance of the algorithm was better as the number of bins in the pulsar signal period increases. This method changed the traditional idea of first denoising and then estimating TOA, which can be embedded in the process of signal denoising, and can be calculated in parallel with the threshold processing of wavelet denoising. The simulation results show that the time consumption of this method is 0.87% and 21.35% of that of the two traditional TOA estimation methods, respectively. And with the shortening of the data duration, the relative advantage of the TOA estimation accuracy of this method is more obvious. This method can not only improve the accuracy of TOA estimation, but also reduce the dependence on the duration of data.