The GaoFen-5 satellite is equipped with a greenhouse gas monitoring instrument (GMI) and a directional polarization camera. Both devices have their own advantages as well as limitations in cloud detection. This study proposes a novel collaborative cloud screening algorithm that uses data from both devices to improve the efficiency of cloud screening for greenhouse gas retrieval. This algorithm is tested with 77581 GMI observation points from the global 16-day on-track measured data, and 9508 clear-sky observation points, i.e. 12.26% points are screened. With the fused moderate resolution imaging spectro-radiometer cloud mask and cirrus reflectance dataset, the validity of cloud detection by the proposed algorithm is confirmed. The accurate rates of cloud detection of 92.93% and 81.91% over land and oceans are obtained, respectively.

Based on the hourly observational data of the aerosol scattering coefficient and the aerosol absorption coefficient as well as the coincidental data monitored by the GRIMM180 environment particle monitor in Chengdu during the period from September to December in 2017, the real and imaginary parts of the equivalent complex refractive index of “dry” aerosol at 550 nm were calculated using an immune evolutionary algorithm; subsequently, the correlations between these quantities and the primary index of mass concentration were further investigated. The results denote that the real and imaginary parts of the equivalent complex refractive index of “dry” aerosol are 1.55±0.045 and 0.022±0.0075, respectively. With respect to the change in the real part of the equivalent complex refractive index of “dry” aerosol, the most important mass concentration indexes of particles are the respective mass concentration ratios between particles having diameters smaller than 1 μm and particles having diameters smaller than 10 μm and 2.5 μm, and the corresponding determining coefficients are 0.53 and 0.21, respectively. With respect to the change in the imaginary part of the equivalent complex refractive index of “dry” aerosol, the most important mass concentration indexes of particles are the respective mass concentration ratios between black carbon and particles having diameters smaller than 10 μm and 2.5 μm, and the corresponding determining coefficients are 0.47 and 0.42, respectively.

To address the problem associated with the relatively low temporal resolution of the multi-axis differential optical-absorption spectroscopy used for reconstructing images, we introduce a method to reconstruct the two-dimensional spatial distribution of SO2 gas by combining the imaging differential absorption spectroscopy technology with the non-negative least square method. The sampled column density data are preprocessed using a Savitzky-Golay filter, the sequential coordinate-wise algorithm is used for reconstruction, and Kriging interpolation is used to smooth the reconstructed image. The numerical simulation results demonstrate that the nearness index of the reconstructed image is the lowest (0.11). The experimental results show that the time required to collect data and reconstruct an image using the proposed method is 52.37 s, which is applicable to the capture of the transient concentration of a plume cross section and the real-time reconstruction of SO2 distribution.

The function transfer method is primarily used for the numerical calculation and analysis of non-diffracting optical lattices. But it has complicated mathematical expressions and the programming is challengeable as well. These features make the method difficult for flexibly analyzing the influence of individual optical component as well as its defects and the optical structure on the physical formation of optical lattices. Here, we propose a simulation approach to make the analysis easier. With this simulation method, typical lattices structure, such as fundamental square lattices, maximum symmetric combined fundamental square lattices, and first sparse square lattices, were realized. The non-diffraction performance of the structured beam was verified. These results illustrate the feasibility of the proposed method. Furthermore, the method is useful to find out the correlations among the optical system structure, optical components and the optical lattices. It helps to clarify the formation mechanism and the regulation method of non-diffracting two-dimensional optical lattices and, thus, to develop the potential application.

To clarify the mechanism associated with the deterioration of optical cameras in orbit due to radiation, a heavy-ion irradiation test was performed on an 8-transistor (8T) global shutter complementary metal oxide semiconductor (CMOS) image sensor. The experimental results denote that radiation exposure to different functional modules leads to different abnormalities in the resulting images, including forcing the output image to be always zero, the creation of output anomalies in several adjacent column outputs, and the corruption of data over the whole image. Further, the effect of the microcosmic process of the heavy-ion irradiation in the device on the macrocosmic abnormal regions of the resulting images are analyzed for various sub-circuit functions, process structures, and working principles of devices. This analysis provides an overview of the sensitivity and damage mechanism with respect to the different functional modules of the camera sensor. These research results provide significant reference data for the radiation-proofing design of CMOS image sensors, the experimental methods for single-event simulation on the ground, and the establishment of standards and assessment techniques.

Introducing a blocking barrier with a wide bandgap can effectively lower the dark current of a traditional pn-junction infrared photodetector. The energy band diagrams of detectors are obtained by simulation using COMSOL software, and the simulation denotes that n- or p-type doping of the InAsSbP quaternary alloy sinks the valence band and lifts the conduction band in its energy map, thereby blocking holes or electrons. Through the theoretical analysis and simulation calculations, the compositions of InAsSbP necessary to satisfy the requirements of the blocking barrier are determined. The optimal values of the blocking-barrier thickness and doping concentration (particle-number concentration) are provided for the nBip and pBin infrared photodetectors by simulation, respectively. Further, the effects of the deviations from these optimal values on the dark currents of devices are analyzed. For the nBip detector, the maximum on-off ratio is obtained when the thickness and doping concentration are 40 nm and 2×1018 cm-3, respectively, while for the pBin detector, the thickness and doping concentration are 60 nm and 4×1017 cm-3, respectively.

Considering the advantages of the unit vector method, a method is proposed for the initial orbit determination (IOD) of space targets using a camera array. The novel condition equations and details regarding the process are given. A space target is tracked by a custom-built camera array system, and the data from a 5-min long observation at 25-Hz frame rate are processed and calculated. The IOD results for the space target at different observation times are obtained, and their accuracy is analyzed by using the measurement accuracy of the orbital semi-major axis as the main indicator. The experimental results show that the proposed method effectively reduces the IOD error and enhances the IOD stability.

A timing synchronization algorithm based on a pseudo-noise (PN) sequence is proposed aiming at the problems of sub-peak interference and timing instability at low signal-to-noise ratio (SNR) in the traditional timing synchronization algorithms. The structure of the training sequence is reconstructed and the calculation method of the timing measurement function is optimized by utilizing the good delay correlation and symmetric correlation of the PN sequence. The simulation results show that only one peak can be seen in the timing metric estimation curve and the sub-peaks are suppressed by using the proposed algorithm. The algorithm can realize accurate and stable timing synchronization, even when the length of the cyclic prefix is a quarter of the symbol length and the SNR is low.

In this study, we propose and design the structure of a graphene-based D-shape twin-core fiber (DTCF) modulator by utilizing the unique absorption characteristics of graphene and the coupling between two cores, which integrates the advantages of absorption modulation and coupling modulation. Further, the modulation feasibility of this structure can be verified using numerical simulation. Subsequently, the effects of the transmission mode, two core radius, twin-core distance, number of graphene layers, and transition layer materials of the modulator on the performances are analyzed based on the finite element method. Finally, a high-performance modulator with a modulation bandwidth of 8.557 GHz, an extinction ratio of 67.64 dB, a half-wave voltage of 1.763 V, a modulation depth of 98.75%, an insertion loss of 1.4 dB, and a modulator length of 3.07 mm can be achieved through optimization.

In this study, we presented the design and testing of a microwave photonic filter with switchable single- and dual-passband operation based on stimulated Brillouin scattering. By adjusting the interval between the wavelengths of the pump light and the signal light, the filter can be switched from single- to dual-passband operation. Moreover, the passband frequency can be tuned. In addition, we prepared a theoretical model of this device and made the corresponding simulation. The analysis was verified using a proof-of-concept experiment. The experimental results show that the rejection ratio can be up to 30 dB, and the frequency tuning range is approximately 0-18 GHz. The experimental results are observed to agree well with the simulated results.

Low security and high peak-to-average power ratio (PAPR) are two major challenges for orthogonal frequency division multiplexing passive optical network (OFDM-PON) systems. This study proposes a secure selective mapping (SLM) scheme based on two-dimensional chaotic encryption. The subcarriers of OFDM signals are scrambled by the random interleavers and phase sequences generated using a two-dimensional logistic map to achieve both encryption and PAPR reduction. The simulation results show that compared with the conventional SLM and original optical OFDM (O-OFDM) signals, the proposed scheme can obtain PAPR suppression gains of 0.5 dB and 3.8 dB, respectively. The experimental results demonstrate that a 7 Gbit/s 16-quadrature-amplitude-modulation (16QAM) O-OFDM encrypted signal can be securely transmitted in the intensity modulation/direct detection OFDM-PON system through a 25-km standard single-mode fiber. Moreover, the bit error rate performance of OFDM-PON systems is considerably improved.

Circular core fibers have been gradually replaced with polygonal core fibers in the high-precision radial velocity measurement systems. Further, the scrambling schemes combining polygonal fibers, lenses, or circular fibers have been subsequently proposed. This study simulated the scrambling properties of circular and octagonal fibers together with the double-fiber scrambler based on these two fibers using the ray tracing method. The simulation results show that although circular fibers have good angular scrambling properties in both the far and near fields, their radial scrambling properties are not good. For octagonal fibers, the near field scrambling is better than that of circular fibers, whereas their far field scrambling is not obviously different from that of circular fibers. A double-fiber scrambler can effectively improve the fiber scrambling performance. In addition, a double-fiber scrambler with octagonal fibers exhibits excellent scrambling performances in both the far and near fields.

We fabricated a PbS quantum-dot-doped photonic crystal fiber (QD-PCF) working in the near-infrared range of 1400-1650 nm and measured its absorption of 980 nm pump light and 1550 nm signal light. Upon the excitation of 980 nm pump light, we acquired the photoluminescence (PL) spectrum of the QD-PCF and determined the doping concentration (mass fraction) and fiber length that maximized the PL intensity at the central wavelength of 1550 nm. The PL intensity of the QD-PCF far exceeded that of the usual single-core quantum-dot-doped fiber (QDF), appearing multiple intensity peaks spacing a short distance. The intensities of these peaks were related to the doping concentration. Comparing the QD-PCF with the un-doped PCF, the bandgap was not found to be changed by quantum-dot doping. The threshold and saturated pump powers of the QD-PCF were also measured. The threshold pump power approximated that of the QDF, but the saturated pump power exceeded that of the QDF, owing to the larger fiber section and higher doping concentration in the QD-PCF.

To address the problem of random polarization deflection in fibers, we propose an optimization method for instantaneous frequency measurements based on stimulated Brillouin scattering. The feature difference is analyzed by comparing how a single-mode fiber and a polarization-maintaining fiber affect the realization of instantaneous frequency measurements based on stimulated Brillouin scattering. The experimental results show that random polarization deflection is well suppressed in the polarization-maintaining fiber compared with that in the single-mode fiber. Further, the frequency resolution of the measurement system with the polarization-maintaining fiber is improved from 225 MHz to 90 MHz.

In this paper, a partially developed speckle model for millimeter-wave holographic imaging with specular reflection is established. The partially developed speckle model is combined with the convolution process of millimeter-wave holographic imaging. The number of equivalent scattering centers is deduced, and the relationship among speckle contrast, root-mean-square height, correlation length, and imaging resolution of a Gaussian rough surface is established. The Monte-Carlo simulation experiment and the speckle contrast analysis are conducted on the millimeter holographic speckle patterns of a random rough surface based on the near-field physical optics method. The results show that when the number of equivalent scattering centers is small, the speckle contrast estimated using the proposed model is consistent with those estimated using the stochastic integral method and the simulation experiment, which is superior to the estimation results of the conventional models.

This study proposes a fast algorithm for nose tip localization, which is robust to pose variations. Based on the coordinates of the local reference frame (LRF), the plane-distance energy of each vertex is calculated and a novel iteration algorithm for selecting candidate points is designed. For each vertex with centralized candidate points, the divergence on the three-dimensional (3D) vector field is computed. The nose tip denotes the point with the maximum divergence value. The efficiency of the algorithm is verified by applying it to the FRGC v2.0 and Bosphorus face libraries. The average runtime of nose tip location is only 0.62 s on the Bosphorus library, whereas the location accuracy is 95.6% on the FRGC v2.0 library. Finally, compared with other state-of-the-art algorithms, the proposed algorithm ranks the first both in speed and accuracy. The results show that the proposed algorithm can meet the requirements of real-time processing, has relatively high accuracy, and is robust to the pose variations in human faces.

An image matching algorithm is proposed to address the poor robustness and low matching efficiency exhibited by the affine scale-invariant feature transform algorithm used for image matching with a large viewing angle. The proposed algorithm employs nonlinear diffusion filtering to preprocess images instead of Gaussian linear filtering, thereby improving the robustness of the detected feature points. Further, a mask operator is employed to denote the effective region in the image simulation transformation process for improving the detection efficiency of feature points. According to the angle simulation transformation principle, the neighborhood information can be extracted from the feature points at different view transformation angles, and the multi-view nearest neighbor matching and weighted matching rules are proposed to establish a multi-view descriptor, thereby improving the matching efficiency. The experimental results show that the proposed algorithm not only exhibits good robustness when the viewing angle changes, but also improves the image matching efficiency and accuracy compared with the existing feature matching algorithms.

In this study, a scheme is constructed based on multi-channel parallel detection to improve the quality of photon-counting correlated imaging. Further, the imaging performance of the constructed scheme is analyzed and verified using numerical simulation. Subsequently, the influences of the detection channel number, the average level of the echo signal photon, and the sparsity of the irradiation speckle field on the imaging quality are discussed. The numerical simulation results show that the imaging quality is positively correlated with the detection channel numbers in this scheme. The imaging quality is first improved and then degraded with an increase in the average level of the echo signal photon and the sparsity of the irradiation speckle field.

To satisfy the requirements of wide spectrum and miniaturization in space applications of aerospace loads, this study proposes a design method for a double-channel hyperspectral imaging system based on curved prisms. This spectrometer can realize visible and shortwave infrared spectral detection using only one device. The two channels share the same off-axis three mirror system and the partial spectrometer. Via a color separation film placed before the image plane, the visible light is completely reflected, while the short-wave infrared light is completely transmitted by the film. These channels are then detected using different detectors. Herein, the double-channel imaging spectrometer is designed that can measure from 420 to 2500 nm. The design results show that the spectrometer has a simple structure, and can achieve high resolution at a total length of <350 mm. Compared to the traditional wide spectrum imaging spectrometer, the designed spectrometer is compact and has low cost, thus making it suitable for broadband space applications.

Tabletop nanoscale microscopy can be performed using X-ray Fourier-transform ghost imaging (FGI). However, the X-ray source used in a tabletop FGI system is one miniaturized laboratory source with poor monochromatic quality, making it difficult to directly obtain high-quality diffraction patterns from a sample. To obtain high-quality patterns, the theoretical derivations and numerical simulations on FGI using a polychromatic source were performed. The mechanism of the influence of polychromatic light on the distortion of diffraction patterns in FGI was clarified, and further a diffraction-pattern correction method was proposed. Based on the scaling relation between the different X-ray wavelengths and the corresponding diffraction patterns, a matrix equation was derived linking the diffraction pattern of a sample and the polychromatic-intensity correlation function, using which the diffraction pattern of the sample can be obtained.

The influence of surface elevation on atmospheric CO2 observations is explored from the perspective of forward and inversion of the atmospheric radiation transfer model in this work. The surface elevation data from the shuttle radar topography mission (SRTM) show that the error of the mean surface elevation due to inaccurate satellite pointing in the plains near Beijing is small, with a maximum error of approximately 10 m for a pointing offset of 0.1-10 km. However, in the mountainous areas and in the boundaries between mountainous areas and plains, the error of the mean surface elevation is large, with the maximum errors of 713.98 and 515.61 m, respectively. The CO2 inversion results show that for an elevation change of 100 m, the CO2 column density deviates by 3.29×10-6. Thus, the research results show that the surface elevation deviation is a critical factor in performing atmospheric CO2 inversion with high precision.

In this study, a jitter estimation algorithm during the acquisition period of non-overlapping images was proposed based on a double-constraint function. The double-constraint function was derived by combining the parallax-observation images with the low-frequency jitter to evaluate the smoothness of the jitter curve during the acquisition period of non-overlapping images. The conjugate-gradient method was used to find the smoothest curve, and the corresponding solution was used as the optimum estimation of jitter during the acquisition period of non-overlapping images. The quantitative relation between the jitter during the acquisition period of non-overlapping images and that during the acquisition period of overlapping images was established. The experimental results using the Chinese XX-1 space camera show that the jitter detection results are only valid when the measured jitter frequencies are neither equal nor close to any integer multiple of the characteristic frequency. This in turn proves that in such cases, the proposed algorithm can effectively detect the jitter during the acquisition period of non-overlapping images.

Herein, a technique for plasma diagnosis via laser interference is described in terms of basic principles, experimental setup, and image-processing methods. Air-switch plasma is diagnosed using a Mach-Zehnder laser interferometer. The results show that the experimental device can record high-quality interferograms. Through numerical processing of these interferograms, the three-dimensional electron density distribution in plasma is reconstructed. After the air switch is ignited for 75 ns, the average electron density in plasma reaches 2×1018 cm-3, the electron temperature is 0.11 eV, the plasma radius is 1.1 mm, and the diffusion velocity is 1.4×104 m/s.

The heat dissipation rate between a CaF2 optical micro-cavity bulk and the environment can be detected by measuring the thermo-optic oscillation period. However, there exists a nonlinear relation between the heat dissipation rate and multiple oscillation periods, and thus the heat dissipation rate cannot be effectively detected at a certain oscillation period. A sensing data measurement model based on the back-propagation artificial neural network was applied, and the heat dissipation rate was effectively measured by measuring the oscillation periods. The neural network parameters were optimized to improve the measurement accuracy of heat dissipation rate. The numerical simulation results demonstrate that the proposed method can effectively detect the heat dissipation rate in a CaF2 optical micro-cavity, which is essential for realizing thermal parameter sensing based on an optical micro-cavity.

An important method to observe stratospheric winds is to invert the Doppler frequency shift of fine spectra with a Michelson interferometer using an O3 radiation probe source in the 8.823-μm waveband. Therefore, the spectral characteristics of O3 limb radiation were analyzed to determine the best target spectral line. The target spectral line was extracted via the combined filtering of a three-level infrared Fabry-Perot etalon. The four-step interferometric images were obtained during daytime and nighttime limb-viewing with the established numerical model of the Michelson interferometer. Via an error analysis, the result was validated to ensure that, in the range of 15-45 km, the measurement errors of the wind in the line of sight are within a range of 1-2 m/s for both daytime and nighttime observations. Consequently, the stratospheric winds can be detected globally and round the clock using a Michelson interferometer with O3 radiation as the probe source.

A Schmidt corrector plate for cancelling the aberrations of spectrometers is designed based on the principle of a Schmidt system. A formula for the surface shape and a surface map of the Schmidt corrector plate are derived. Then, the imaging characteristics of the spectrometer systems with and without the Schmidt corrector plate installed are simulated and analyzed using the ZEMAX software. The results show that for the wavelengths of 350, 550, and 700 nm, the root-mean-square (RMS) radii of light spots on the image plane of the original spectrometer are 515.843, 563.074, and 885.820 μm, respectively. In contrast, with the Schmidt corrector plate installed, the RMS radii of light spots on the image plane are 287.441, 252.774, and 511.816 μm, respectively. For the wavelengths of 350, 550, and 700 nm, the spot sizes with the Schmidt corrector plate installed are reduced by 44.28%, 55.11%, and 42.23%, respectively. The proposed method for designing a Schmidt corrector plate provides a technical reference for improving the resolution of spectrometers.

Herein, a metal-insulator-metal asymmetric circular structure comprising two circular cavities, a transmission waveguide, and two coupled waveguides is proposed. The coupling effect of surface plasmon polaritons is strengthened through the local effect of resonant cavities, and a good extraordinary transmission is obtained. The effects of the radii and number of circular resonant cavities and that of the inter-circle distance on such an extraordinary transmission are investigated via the finite difference time domain method. The results show that in the case that the radius of the circular resonant cavity resonator and the inter-circle distance are 100 nm and 200 nm, respectively, the structure exhibits a very good extraordinary transmission. The optimization of these main parameters could allow an average stopband width of 1000 nm and increase the working range up to 2500 nm.

Al2O3-reinforced Fe901 metal-ceramic composite coatings were prepared by laser cladding to improve the wear resistance of surface coating of metal materials. This study investigated the effect of Al2O3-reinforced phase on the microstructure and properties of a Fe-based cladding layer. The microstructural evolution, phase compositions, wear resistance, and microhardness of the composite coatings were studied using scanning electron microscopy, X-ray diffraction, friction and wear tester, as well as microhardness tester, respectively. The results show that the microstructure of the Fe901 coating was dominated by columnar and equiaxed dendrites. In addition, the addition of Al2O3 promoted the transformation of microstructure into a uniformly distributed white network-like intergranular structure with wrapped fine black grains. The surface of Al2O3 ceramic particles micro-melted and combined with Fe and Cr to form Fe3Al and (Al, Fe)4Cr intermetallic compounds within the composite coating, which increased the bond strength between Al2O3 ceramic particles and the metal phase. When the mass fraction of Al2O3 ceramic particles is 10%, the microhardness of the composite coating is increased by 16.4%, and the mass loss in the composite coating is reduced by 50% compared to that of the Fe901 coating. Thus, adding an adequate amount of Al2O3 ceramics can improve the microhardness and wear resistance of coatings.

This study reports on a stable single-frequency active Q-switched Nd∶YVO4 laser end-pumped by a continuous-wave laser diode. The stable high power single-frequency laser output is obtained using reflective Bragg grating (RBG) and etalon. RBG is used as an output coupling mirror and a longitudinal mode selector, combining with etalon to further suppress multiple longitudinal modes, the optical cavity length is increased and high power output is achieved. By optimizing the tilt angle of etalon, the central wavelengths of etalon and RBG can be matched and the insertion loss in cavity can be reduced. Finally, at the physical cavity length of 148.7 mm, a high-power single-frequency laser output with an average power of 750 mW, a pulse energy of 75 μJ at a repetition rate of 10 kHz, and a pulse duration of 8.3 ns is obtained.

In this study, we propose a method to recognize and position multiple people with multiple cameras based on the “vibration signals” obtained from their skin surfaces to adapt to an extensive range of scenes. Herein, the principles that the “vibration signals” obtained from the same person can be synchronized using multiple cameras and that the “vibration signals” obtained from different people are different are proposed and verified via experiments. The “vibration signals” are obtained from the human skin surfaces using multiple cameras based on skin-color detection and regional tracking. Further, individuals are recognized based on the difference and synchronization principle and the cosine similarity. Several people are positioned with multiple cameras via coordinate calculations, and the maximum positioning distance error is 61.01 cm.

To solve the problems of illumination variation, occlusion, and scale variation during object tracking, we propose a multi-scale context-aware correlation filter tracking algorithm based on channel reliability. First, we extract the histogram of the oriented gradient (HOG), gray features, and color name (CN) features as the appearance model of the object, which can enhance the robustness of the tracking algorithm in a complex scene. Second, the single-channel context-aware correlation tracker is independently trained by applying the related channel feature samples. The channel reliability factor is applied to evaluate the confidence of each channel. Then, the final response map of the multi-channel context-aware correlation tracker comprises the response maps and the channel reliability values of all the channels, and it is used to accurately locate the object. Finally, the scale pool method is applied to estimate the optimal position and scale of the object. When compared with the results obtained using the state-of-art trackers, the experimental results show that the proposed algorithm can effectively tackle the illumination variation, occlusion, scale variation, and other complicated factors, and achieve relatively high tracking accuracy and success rate. The overall performance of the proposed algorithm is superior to those of other algorithms.

In this study, three cold soybean varieties, namely Kangxian-9, Kangxian-13, and Fudou-6, were used for the high-throughput calculation of soybean plant heights. Three varieties were used to overcome the disadvantages of the traditional measurement methods, which were inefficient and laborious. The method for calculating the plant heights of individual and grouped soybean plants was proposed using the depth information acquired from the three-dimensional reconstruction of soybean canopies obtained using the Kinect V2.0 synchronous image acquisition platform. The experimental results show that compared with the measured value, the average errors of the proposed calculation method for the plant heights of individual and grouped soybean plants are 0.14 cm and 0.54 cm, respectively. The determination coefficients between calculated and measured values for Kangxian-9, Kangxian-13, and Fudou-6 are 0.9717, 0.9730, and 0.9697, respectively. Thus, the proposed method can accurately calculate the heights of soybean plants.

In this study, an approximate analytical solution of the Laguerre-Gauss-like vortex solitons was obtained after conducting a second-order perturbation correction in lead glass, a kind of strongly nonlocal nonlinear (1+2)-dimensional medium. Specifically, the nonlocal nonlinear Schr dinger equation (NNLSE) was perturbed using the difference between the real and parabolic refractive indices in lead glass, where the parabolic index was described using the Snyder-Mitchell (SM) model. The Laguerre-Gaussian soliton solution in the SM model is considered to be the ground state solution. Further, the perturbation-corrected Laguerre-Gauss-like solitons with topological charges of 1,2,3, and 4 are more stable when compared to those without perturbation, and their propagation behaviors are almost similar to that of the true soliton solution.

This study investigated the correction performance of closed-loop control with hysteresis compensation for a piezoelectric unimorph deformable mirror. A closed-loop control algorithm based on the Prandtl-Ishlinskii hysteresis model was established herein. In addition, an adaptive optics test platform based on the Hartmann wavefront sensor was built. The closed-loop correction experiments of static and dynamic aberrations were performed. The experimental results show that for the closed-loop correction of static aberrations, the correction speed of the algorithm with hysteresis compensation is faster than that without compensation. Further, for the dynamic aberrations with an average root-mean-square value of 168 nm, the residual error after correction is reduced from 33 nm before hysteresis compensation to 25 nm after hysteresis compensation. These results prove that the proposed method can be efficiently used in an adaptive optics system with a piezoelectric deformable mirror.

A miniature chemiluminescence NO sensor is developed using a miniature low-cost PIN photodiode as the photoelectric detector. Five optoelectronic components of the Si detector and InGaAs detector are selected to investigate their relationship with the spectral response of NO luminescence and noise. The experimental results show that the 1.2-mm-length rectangular Si detector is the best one with the advantages of a sensitive response, a low dark-current noise, and the lowest signal-to-noise ratio. Moreover, a small optical cavity is designed, small amount of NO luminescence with a volume fraction of 2×10-6-2×10-4 is measured, and the linearity is 0.9993. The response time of the whole system is approximately 0.13 s and the sensor weight is less than 50 g. Thus the proposed sensor is very suitable for the online monitoring of NO gas in the industrial pollution source.

In this study, we construct a model to calculate the thickness of the adhesive layer in the mirror subassembly of a space camera with a blind taper hole based on different boundary conditions. Further, a mechanical model is used to calculate the adhesive layer thickness range at the bonding part that satisfies the design requirements. Using the constructed finite element model, we calculate and fit the corresponding thickness-stress curve of the adhesive layer, and the optimum thickness is observed to be 0.055 mm. Subsequently, the change in the surface of the mirror subassembly is numerically analyzed under the self-weight and temperature-rise conditions in order to verify the surface shape accuracy of the adhesive structure. The temperature load method is employed to simulate the influence of the adhesive layer shrinkage on the surface, and the subassembly tests are performed. The simulation and test results demonstrate that the mirror subassembly exhibits a sufficient capability to resist the interference of the external temperature variation and vibration at an adhesive layer thickness of 0.055 mm, satisfying the design requirements.

A charge imbalance often occurs in quantum dot light-emitting diodes (QLEDs) owing to the difference in migration rate between the hole transport layer (HTL) and the electron transport layer. In this study, we inserted a Spiro-OMeTAD thin film, an organic polymer with a high lowest unoccupied molecular orbital energy level, between the HTL and quantum dot emission layer to block the transmission of excess electrons from the quantum dot luminescence layer to the HTL, which promotes the charge balance of the device, and thus a highly efficient new green QLED is fabricated. The results show that the new green QLED exhibits distinct improvements over the traditional devices, with an 87% improvement in external quantum efficiency up to 11.87%, and a 106% increase in brightness up to 53055 cd/m2. This proves that blocking the transmission of excess electrons can significantly solve the charge imbalance problem in QLEDs.

Based on the least square method, the average surface rigid-body motion equation of optical elements is derived herein using the area-weighted average motion. By analyzing the effect of micro-vibration on the modulation transfer function (MTF) of an optical system, the relevant image motion and its corresponding optical axis rotation angle are determined. The data process for the frequency response analysis is performed using the average rigid-body motion equations. The micro-vibration magnitude of the photoelectric payload mounting surface is retrieved based on the demands of optical axis rotation angles of the system. The real-time MTF testing of the system is performed using the constant-frequency micro-vibration test. The results show that the error discrepancy between the analysis results and the test data is within 20%, which meets the requirements for engineering applications and verifies the correctness of the computational method.

In the multidimensional reconciliation process of continuous-variable quantum key distribution (CVQKD), the error correction performance of the low-density parity-check code (LDPC) directly affects the reconciliation efficiency and transmission distance. Herein, a two-edge type low-density parity-check code (TET-LDPC) is constructed. We introduce a cumulative structure similar to that of a repeat-accumulate code into the TET-LDPC to improve its error correction performance. These codes obtain a smaller convergence signal-to-noise ratio, whereas the reconciliation system achieves higher coordination efficiency and longer transmission distance. The simulation results indicate that at a TET-LDPC code rate of 0.5 and a block length of 2×105, the convergence signal-to-noise ratio of the system is reduced to 1.02 dB, the data reconciliation efficiency is 98.58%, the security key rate reaches 17.61 kb/s, and the CVQKD transmission distance increases to 44.9 km.

To improve the target location accuracy of a small-scale airborne electro-optical platform, a target geo-location algorithm based on extended Kalman filtering (EKF) is proposed. According to the characteristics of a tracking target locked by the airborne electro-optical platform, the same target is measured repeatedly. Using the aircraft position and attitude information measured by an integrated navigation system as well as the position information of the gimbal angles from the position encoder, the direction of the line of sight for the target is determined according to the Earth ellipsoid model. The state and measurement equations are established, and the geographical position of the target is estimated using EKF. The Monte Carlo method is used to analyze the influence of the measurement error on the target geo-location accuracy. The simulation results demonstrate that the proposed algorithm is highly accurate and robust. The validity of the algorithm is verified by a flight test. At a flight height of 4300 m, the geo-location error of the target is less than 15 m. Compared with that of the algorithm based on the Earth ellipsoid model, the target geo-location accuracy of the proposed algorithm is improved obviously.

In this study, the calibration tests were conducted on the Hyperion hyperspectral remote sensor using the automated observation equipment at the Dunhuang radiometric calibration site. This paper details the principle and method of automated calibration and specifies the applied calibration process. A reference reflectance database was established to solve the problem of mismatch between the channel reflectance in the hyperspectral remote sensor and the spectral shape of the reference reflectance. The results of the four effective automated calibration tests performed on Hyperion from October 2016 to April 2017 were compared with the apparent radiance observed by Hyperion. The results show that the relative deviation between the apparent radiance obtained from the site-automated calibration and that from the satellite observation is less than 5% with a standard deviation of less than 2.3% within the 420-1044 nm spectral range. The site-automated calibration results are found to be highly consistent and stable with respect to the hyperspectral satellite observations, indicating that the proposed method can be applied to the high-frequency on-orbit radiometric calibration of hyperspectral remote sensors.

Achieving high-accuracy localization in urban environments is challenging in autonomous driving. The existing LiDAR-based localization algorithms can ensure high accuracy in most cases; however, the localization problems in complex dynamic city scenes still need to be addressed. This study proposes a novel probabilistic localization framework to mitigate the accuracy degradation of the global positioning system caused by occlusion and to reduce the effective point cloud features caused by moving objects and changing environments in such scenarios. The proposed framework combines the improved multi-layer random sample consensus algorithm and the histogram filtering algorithm with the kernel density estimation method; this combination effectively overcomes the localization fluctuation of multi-layer random sample consensus in some scenes as well as the inefficiency and local optimum of histogram filtering when the pose error is large. The experimental results indicate that the proposed framework can provide more stable and accurate localization as well as tolerate larger initial pose errors compared with the existing localization methods when applied to complex dynamic city scenes.

A multiple-feature-based improved sparse representation (MFISR) method is proposed herein for the classification of hyperspectral images. The spectral feature, Gabor feature, and local binary pattern (LBP) feature are extracted from the hyperspectral image; subsequently, the sparse coefficients are solved and a 2-paradigm constraint is added. These obtained coefficients are used to determine the final class label of each test pixel. The experimental results demonstrate that the proposed MSIFR method exhibits excellent results for the detection of small samples, and its classification performance is stable and good.

Herein, we propose an improved dynamic threshold cloud detection algorithm (I-DTCDA) for visible infrared imaging radiometers (VIIRS) based on the multi-channel, wide coverage, and short revisit period features of a VIIRS. In addition, the algorithm is also based on the characteristics of the cloud distributions and variations in the visible and thermal infrared channels. We validated the accuracy of the cloud detection results using the remote sensing visual interpretation method. We compared our results with those using the universal dynamic threshold cloud detection algorithm (UDTCDA) and the VIIRS cloud mask (VCM) products. The results show that the proposed algorithm has average overall accuracy of 93% (Kappa=0.821) over different surface features. In particular, for the thin and broken clouds, the overall accuracy is significantly improved and the commission and omission errors are obviously reduced. The cloud detection results using the proposed algorithm are superior to those using UDTCDA and VCM.

In this study, an improved method based on empirical mode decomposition is proposed for the detection of persistent scatterers (PSs). The interferograms are decomposed from different angles, and noises contained in the decomposed intrinsic mode function (IMF) are strongly filtered in the low signal-to-noise ratio regions and weakly filtered in the high signal-to-noise ratio regions based on gradient adaptive filtering; the noise phase of each persistent scatterer candidate (PSC) point is estimated after filtering. Based on the stability of the amplitude and the phase of each PSC point, the phase information of the selected PSC point is analyzed to determine its probability of being a PS point, and the reliable PS points are selected. The experimental results denote that the proposed method avoids misjudgment and omission possibilities in the process of PS point detection with higher accuracy when compared to that exhibited by the traditional PS point detection method.

A new sun glint suppression method is proposed based on polarized radiation image fusion. Herein, the polarization measurement of sun glint is performed using the simultaneous polarization imaging technology and the polarized radiation images of 0°, 45°, and 90° are obtained. In the polarized radiation image with the strongest glint suppression, the residual strong glint region is selected and used to generate a regional glint suppression polarization radiation image based on the calculation of Stokes parameters. The selected polarized radiation image is fused with the regional glint suppression polarized radiation image to further suppress the glint intensity. The indoor experimental results demonstrate that the proposed method can effectively suppress glint and eliminate image saturation. In addition, the obtained fusion image is more uniform than the intensity image, and the target details and contour information are clear, which significantly improves the contrast of the target relative to the flare background.

The commonly used chemical methods result in the destruction of the fingerprint samples; therefore, an optical ultraviolet imaging method is proposed in this study. Further, a mathematical model of the relationship between the radiance ratio and the fingerprint retention time in different ultraviolet bands is derived based on the relative concentration relation between amino acids and urea and the scattering spectral curve theory. In addition, we have developed an ultraviolet multispectral imaging device to perform the lossless fingerprint extraction in three ultraviolet bands. An inversion analysis of the digital number (DN) values of the different-band fingerprint images is conducted to obtain the relationship between the ratio among DN values in different bands and the fingerprint retention time. The experimental results denote that the ratio among the DN values in different ultraviolet bands is only related with time and not with the individual fingerprint difference. Moreover, the expression of the fingerprint aging curve fitting is consistent with that provided in the derived mathematical model, and the feasibility of the usage of ultraviolet multipass spectral imaging for conducting the fingerprint retention time evaluation is verified, which provides an important analysis method for performing the non-destructive fingerprint aging evaluation.

Herein, based on the fluorescence detection mechanism, acenaphthene, fluorene, and naphthalene were detected in polycyclic aromatic hydrocarbons by the parallel factor combined with the support vector machine (SVM) algorithm. The fluorescence spectral data were preprocessed and used as the training set, which was fed into the particle-swarm-optimized SVM algorithm to establish the classification model. The number of components was determined using the methods of core consistency analysis, residual square sum analysis, and iterative frequency analysis, and the optimal component number thus obtained was used to perform parallel factor decomposition. The obtained transmit load matrix was used as the test set and fed into the SVM classification model. The classification accuracy rate was 100%. The recovery rates of 100.45%±6.25%, 100.10%±6.39%, and 95.07%±7.46% were achieved for acenaphthene, fluorene, and naphthalene, respectively. The proposed algorithm avoids time complexity caused by human operation and errors caused by subjective factors. Thus, it can be applied for fluorescence detection of polycyclic aromatic hydrocarbons.

Under the open light path condition, the spectral characteristics of polluted gases and atmospheric components are overlapped, making it difficult to directly identify the polluted gases. This study proposes an adaptive feature extraction method, which pre-generates the spectral features under various atmospheric conditions. The rapid feature extraction is performed using the Lasso algorithm for selecting the optimal target-background combination, reconstructing the background spectrum, and extracting the target features. The effectiveness of the proposed algorithm is verified via the methane remote detection under different backgrounds; the ammonia gas detection is also performed under different relative humidity conditions along with the indoor close-range ethylene detection. The proposed method is compared with the Harig's method. The results show that the proposed method can well eliminate background and possesses strong practicability.

A six-layer thin-film sample constructed from the transition metal W and dielectric material SiO2 is prepared through the magnetron sputtering apparatus. The microstructure of the film is Cu(>100.0 nm)/SiO2(63.5 nm)/W(11.0 nm)/SiO2(60.0 nm))/W(5.4 nm)/SiO2(75.5 nm). The fabricated sample has a solar absorptance of 95.3% in the wavelength range of 250-2500 nm. Under the low vacuum (6 Pa) condition, the reflectance characteristics of the sample after annealing at 400 ℃ for 72 h show no obvious change, which proves that the sample has an excellent thermal stability. In addition, an infrared thermal imager is adopted for the real-time and in-situ characterization of the infrared radiation from the sample and it is proved that the sample has a low radiation characteristic. These unique properties imply that the sample is highly suited for its application in solar thermal conversion.

In this paper, we propose a dehazing algorithm based on the dark-channel image centroid offset. The algorithm clusters the dark channels of hazy images to divide these images into scenes. Further, it analyzes and calculates the centroid offset of the dark-channel image of each scene to correct the transmission rate of the scene. Combined with the quadtree search algorithm, an atmospheric light estimation method based on the depth of field step image is proposed, which enables the estimated position of atmospheric light to fall in a region with a large depth of field without being affected by white or flat objects. The experimental results reveal that the proposed algorithm can effectively restore the original hue of bright regions as well as the detail information. Moreover, the restored images have appropriate brightness and natural color. Subjectively, the restored images have relatively good visual effects. Objectively, the evaluation indexes of the restored images by the proposed algorithm are overall better than those by the dark-channel-prior algorithm.

The technology for barrier-type autostereoscopic displays that uses binocular disparity to display three-dimensional experiences has been maturing gradually. To quantitatively study the effect of color on visual comfort, the measurements of channel independence, constant chromaticity, and color characterization accuracy are needed. This paper reports these measurements recorded from a barrier-type autostereoscopic display that uses a color active matrix liquid crystal with thin film transistor. The results show that the channel independence of the stereoscopic display is poor in the three-dimensional (3D) mode, but it is very good in the two-dimensional (2D) mode. The chromaticity of the display is consistent in both 3D and 2D modes. In both modes, the characterization accuracies of the gain-offset-gamma (GOG) model are 3.64 and 0.99 times the CIELAB color difference Δ E*ab, respectively, and the accuracies of the look-up table (LUT) model are 2.36 and 0.65 times the CIELAB color difference Δ E*ab, respectively. The display in the 3D mode is affected by crosstalk. Therefore, the color characterization in the 3D mode is less accurate than that in the 2D mode. The characterization accuracy of the LUT method is sufficient for the requirements of the most color-vision experiments. However, to achieve accurate color prediction and control, other more accurate color characterization methods are needed to be developed.