2019
2019
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Record 253 of
Title:Beam pointing analysis and a novel coarse pointing assembly design in space laser communication
Author(s):Zhang, Fu rui(1,2); Han, Jun-feng(1); Ruan, Ping(1)Source: Optik Volume: 189 Issue: DOI: 10.1016/j.ijleo.2019.05.079 Published: July 2019Abstract:Nowadays, Small satellites take with high precision and lightweight laser communication terminals become a hot research direction. In this work, factors affecting beam pointing performance have been studied and a novel coarse pointing assembly (CPA) is designed based on flexure technology. The beam pointing performance is influenced by three aspects: Rayleigh distribution pointing error composed of static bias error and dynamic jitter, coupled motion between optical terminal and satellite and point ahead angle. Based on beam pointing requirements, a novel 2-D spatial flexure parallel coarse pointing assembly is proposed. Firstly, the type synthesis of this mechanism is performed and the freedom is verified by screw method. Then the detailed structural design is given. The pivotal component-elliptic arc flexure hinge is optimized by genetic algorithm and its rotation accuracy is less than 10 um. A flexure rod is used in actuating legs which is made rigid by spatial pseudo-rigid body method in kinematic analysis process. Finally, both of forward kinematics and inverse kinematics have been mathematically analyzed and the virtual prototype simulation is performed in Adams. The rotational accuracy can reach to 3 μrad. The position, velocity and acceleration motion curves shown that the platform moves stable which means it's easy to control. This work provides a new idea for future design of space optical communication terminal. ? 2019 Elsevier GmbHAccession Number: 20192206993443 -
Record 254 of
Title:A Sparse Constrained Graph Regularized Nonnegative Matrix Factorization Algorithm for Hyperspectral Unmixing
Author(s):Gan, Yu-Quan(1,2); Liu, Wei-Hua(1); Feng, Xiang-Peng(1); Yu, Tao(1); Hu, Bing-Liang(1); Wen, De-Sheng(1)Source: Guang Pu Xue Yu Guang Pu Fen Xi/Spectroscopy and Spectral Analysis Volume: 39 Issue: 4 DOI: 10.3964/j.issn.1000-0593(2019)04-1118-10 Published: April 1, 2019Abstract:The space resolution of hyperspectral image is influenced due to the restriction of sensor platform, which results in more than one material in one pixel. Such kind of pixel is called mixed pixel. The existence of mixed pixels restricts accurate analysis and application of hyperspectral images. Hyperspectralunmixing technique can factorize mixed pixels to pure material signatures (endmembers) and corresponding proportion (abundance), which makes more accurate material signature available. Unmxing is very important to accurate classification and identification, anomaly detection and quantitative analysis for hyperspectral imagery. Based on linear spectral mixing model, this paper develops an endmember and abundance sparse constrained graph regularized nonnegative matrix factorization (EAGLNMF) algorithm for hyperspectral imagery unmixing. The algorithm is based on nonnegative matrix factorization, and integrates graph regularization and both endmember and abundance sparse constraints to the object function. Graph regularization is used to consider the geometrical structure of the hyperspectral image and sparse constraints can demonstrate the inner manifoldstructure. First, the lost function of EAGLNMF is constructed, and VCA-FCLS method is used as initial value. And then, the value of the parameters is set, including weighting matrix of graph regularization, sparse factors for both endmember signature matrix and abundance matrix. At last, the iteration equations for endmember matrix and abundance matrix are both obtained, and stopping criteria is given. The algorithm does not require pure pixel in the hyperspectral image. In fact, there are little pure pixel in real hyperspectral imagerydue to the sensors platform. Thus, EAGLNMF algorithm provides a kind of solution for real hyperspectral imagery. The availability and effect of EAGLNMF are verified by synthetic data via four experiments. The experiments compare EAGLNMF with VCA-FCLS, standard NMF and GLNMF. Two metrics, spectral angle distance (SAD) and abundance angle distance (AAD) are used to compare the four methods. Experiment 1 is total comparison experiment of the four methods. SNR and the number of endmembers are constant, and the value of SAD and AAD are compared. Experiment 2 evaluates the influence of SNR. Different value for SNR and constant value for number of endmembers are given to different runs. Experiment 3 evaluates the influence of number of endmembers. Different value for number of endmembers and constant value for SNR are given to different runs. The experiment result shows that EAGLNMF method obtains more accurate result for both endmebers and abundance. Moreover, experiment 4 evaluates the influence of sparse factor between endmember signature and abundance. The result demonstrates that endmember sparse constraint shows a positive effect to unmixing. And, sparse factor between endmember signature and abundance shows effect to unmixing result. In addition, real AVIRIS hyperspectral image is applied to VCA-FCLS, standard NMF, GLNMF and the proposed EAGLNMF, and compared with the ground truth of USGS, the result shows that EAGLNMF obtains best unmixing result among the four algorithms and the accuracy of the estimated endmembers is good. ? 2019, Peking University Press. All right reserved.Accession Number: 20192407043562 -
Record 255 of
Title:A Mueller matrix measurement technique based on a division-of-aperture polarimetric camera
Author(s):Ju, Haijuan(1,2); Ren, Liyong(1); Liang, Jian(1); Qu, Enshi(1); Bai, Zhaofeng(1)Source: Proceedings of SPIE - The International Society for Optical Engineering Volume: 10839 Issue: DOI: 10.1117/12.2506569 Published: 2019Abstract:When an object is illuminated by an incoming light described by a Stokes vector, the outgoing light scattered, reflected or transmitted from the object is modulated and its polarization property can be expressed by another Stokes vector. The transformation relation between the incoming and the outgoing Stokes vectors is called the Mueller matrix. The Mueller matrix completely characterizes the optical properties of the light scattered or transmitted from the object, including the diattenuation, the retardance and the depolarization. So, how to measure the Mueller matrix efficiently and accurately becomes considerably significant for its practical applications. We propose a new method for Mueller matrix fast acquisition based on a division-of-aperture simultaneous polarimetric imaging technique. Traditional methods for obtaining the 16 elements of the Mueller matrix require at least 16 polarimetric measurements. While in our method it is enough by just changing the states of polarization (SOPs) of the input light 4 times. These time-saving and easy calculating features are contributed to our specific polarimetric camera, where a full-Stokes vector is obtained easily since 3 linear SOPs (0°, 45°, 90°) and 1 circular SOP can be recorded simultaneously by sharing the same detector. To simply verify the effectiveness of our method, polarizers (45°, 90°), and quarter-wave plates (0°, 45°) are chosen as samples to be measured. Experimental results show that they are consistent with the theoretical results, both in the Mueller matrix and the corresponding images. We predict that this method for Mueller matrix rapid acquisition can get wide potential applications. ? 2019 SPIE.Accession Number: 20190706489056 -
Record 256 of
Title:Star identification algorithm based on oriented singular value feature and reliability evaluation method
Author(s):Wei, Xin(1,2); Wen, Desheng(1); Song, Zongxi(1); Xi, Jiangbo(3)Source: Transactions of the Japan Society for Aeronautical and Space Sciences Volume: 62 Issue: 5 DOI: 10.2322/tjsass.62.265 Published: 2019Abstract:A full-sky autonomous star identification algorithm aimed at solving the "lost-in-space" problem is presented in this paper. It mainly consists of two steps: an initial match step and a reliability evaluation step. Oriented singular value feature matching is adopted to search for corresponding candidates of the stars detected in the initial match. After obtaining the stars' initial match results, an evaluation method is applied to estimate the reliability of candidates from the star voting results, acquiring the final unique matching of stars in the image. Experiments show that our algorithm is more robust to star position noise and magnitude noise than the two conventional algorithms. In the simulations, our algorithm achieves an identification rate of 97.0% with 2-pixel star position noise and 0.3 Mv star magnitude noise, and also performs well with false stars in the field of view. In addition, the memory requirement and identification time of our method are acceptable for actual engineering projects. ? 2019 The Japan Society for Aeronautical and Space SciencesAccession Number: 20193907480486 -
Record 257 of
Title:Athermal design of refractive/diffractive hybrid infrared optical system with large relative aperture
Author(s):Jiang, Yanru(1,2); Xie, Qingkun(1,2); Qu, Enshi(1); Ren, Liyong(1)Source: Proceedings of SPIE - The International Society for Optical Engineering Volume: 10840 Issue: DOI: 10.1117/12.2504864 Published: 2019Abstract:Infrared detection system, due to its high stability and all-weather adaptability, has been widely applied in civil and military areas. In this paper, based on the refractive/diffractive hybrid structure and the passive athermalization, a dualband infrared optical system with large relative aperture (F=1) is designed, which has excellent performance in the correction of thermal aberration, chromatic aberration and second spectrum between-40°C to 60°C. By precisely arranging the double-layer diffraction element, the system designed is simplified effectively, which contains only four lenses. Meanwhile, the optical layout has the advantages of lower weight and smaller volume. The MTF in mid-wave infrared is larger than 0.6, which demonstrates good capacity of target recognition and anti-inference, and thus it is suitable for practical usage in the field of aviation remote sensing. ? 2019 SPIE.Accession Number: 20190706497365 -
Record 258 of
Title:Remote Sensing Image Scene Classification Using Rearranged Local Features
Author(s):Yuan, Yuan(1); Fang, Jie(1,2); Lu, Xiaoqiang(1); Feng, Yachuang(1)Source: IEEE Transactions on Geoscience and Remote Sensing Volume: 57 Issue: 3 DOI: 10.1109/TGRS.2018.2869101 Published: March 2019Abstract:Remote sensing image scene classification is a fundamental problem, which aims to label an image with a specific semantic category automatically. Recently, deep learning methods have achieved competitive performance for remote sensing image scene classification, especially the methods based on a convolutional neural network (CNN). However, most of the existing CNN methods only use feature vectors of the last fully connected layer. They give more importance to global information and ignore local information of images. It is common that some images belong to different categories, although they own similar global features. The reason is that the category of an image may be highly related to local features, other than the global feature. To address this problem, a method based on rearranged local features is proposed in this paper. First, outputs of the last convolutional layer and the last fully connected layer are employed to depict the local and global information, respectively. After that, the remote sensing images are clustered to several collections using their global features. For each collection, local features of an image are rearranged according to their similarities with local features of the cluster center. In addition, a fusion strategy is proposed to combine global and local features for enhancing the image representation. The proposed method surpasses the state of the arts on four public and challenging data sets: UC-Merced, WHU-RS19, Sydney, and AID. ? 1980-2012 IEEE.Accession Number: 20191106643944 -
Record 259 of
Title:Optical system design for wide-angle airborne mapping camera with diffractive optical element
Author(s):Zhang, Jian(1,2); Zhao, Liangxiao(2,3); An, Fei(2); Hao, Sanfeng(2,3)Source: Proceedings of SPIE - The International Society for Optical Engineering Volume: 11052 Issue: DOI: 10.1117/12.2520554 Published: 2019Abstract:With the development of the digital airborne photogrammetry technology, the more performances of the optical system for airborne mapping camera are required, such as the longer focal and the wider field of view (FOV). At the same time, the secondary spectrum correction becomes more important and difficult for the optical system design. A high performance optical system of airborne mapping camera with 200mm focus and 2ω=60° FOV is designed in this paper. The range of work wavelength is from 430nm to 885nm. A two-layer HDOE with negative dispersive characteristic is used to eliminate the secondary spectrum in the process of optical system design. The diffraction efficiency of the designed two-layer HDOE is up to 90%. From the result of design, the MTFs in whole fields are over 0.5 at 90lp/mm, which shows that the system has a great image quality. Meantime, the thermal analysis is done at the temperature range between-20°C and 40°C. As a result, MTF curves of the system at-20°C ～40°C show that a great image quality is kept, which meets the design requirements. ? 2019 SPIE.Accession Number: 20190806535032 -
Record 260 of
Title:Mechanical performance of magnetic flux-pinging mechanism in space large segmented reflect mirror
Author(s):Zhang, Hao-Su(1,2); Shangguan, Ai-Hong(1); Chu, Chang-Bo(1); Wen, Yan(1); Li, Chuang(1)Source: Guangxue Jingmi Gongcheng/Optics and Precision Engineering Volume: 27 Issue: 12 DOI: 10.3788/OPE.20192712.2609 Published: December 1, 2019Abstract:Mechanical connection mechanisms used in space optical systems experience problems with lubrication, thermal expansion coefficient matching, problems related to its complex structure, and small docking eccentricities. In this study, a flux-pinning interface scheme, which can be applied to a large segmented reflect mirror in space, was proposed. The mathematical model that contained the current equivalent distribution model was built and calculated by the H-formulation method, then, verification experiments were designed to demonstrate the effectiveness of the model. The relationship between the levitation force, stiffness, and relative position of the flux pinning interface under three working condition was obtained using the finite element method. The results indicate that when the distance between the superconductor and permanent magnet is 5 mm, the stiffness of the vertical direction ky can reach 7 000 N/m; when the distance between the superconductor and permanent magnet is 10 mm and it is in a central position, the stiffness of the lateral direction kx can reach 3 800 N/m. The stiffness of the vertical direction ky when Δx=4 mm drops by 20% as compared with the one with Δx=0 mm, therefore, the mechanism can provide greater Δx values than traditional mechanisms and sufficient stiffness, which can also be used for buffering when docking. ? 2019, Science Press. All right reserved.Accession Number: 20200508108062 -
Record 261 of
Title:Design of off-axis three-mirror freeform optical system with wide field of view
Author(s):Ni, Dongwei(1,2); Li, Xuyang(1); Ren, Zhiguang(3); Wang, Yuming(1,2); Wang, Lei(1,2); Tian, Chunlin(1,2)Source: Proceedings of SPIE - The International Society for Optical Engineering Volume: 10837 Issue: DOI: 10.1117/12.2504915 Published: 2019Abstract:In order to obtain a wider imaging field of view, freeform surface is used to design a large field of view space optical imaging system. The system uses an off-axis three-mirror optical structure with focal length of 1600 mm, F number of 8, and field of view angle of 20°×1°. Because of the large field of view, the image quality of general aspheric optimization design system cannot meet the requirements. In order to improve the freedom of system design, the Zernike polynomial freeform surface is applied to the tertiary mirror of the system, which enables the sagittal field of view to reach 20° further widening the imaging field of view. Degrees of freedom are increased effectively by the addition of the freeform surface. After optimization design, the optical transfer function of the system is better than 0.5 at 63 lp/mm, and the diffusion spot is optimized into Airy circle. The system energy concentration is high, and the imaging quality is close to the diffraction limitation. ? 2019 SPIE.Accession Number: 20190506432475 -
Record 262 of
Title:Optimum design of flexible support structure for space mirror
Author(s):Sun, Li Jun(1,2); Zhang, Yuan Qing(2); Li, Si Yuan(3); Zhang, Zhao Hui(3); Li, Li Bo(3)Source: Proceedings of SPIE - The International Society for Optical Engineering Volume: 11341 Issue: DOI: 10.1117/12.2543127 Published: 2019Abstract:To minimize the assembly stress and thermal stress introduced by the support structure, and ensure the high surface accuracy and high thermal stability of space mirror. An ultra-lightweight design of secondary mirror was carried out for some space remote sensor, and three tangential bipods were used for quasi-kinematic support. Firstly, the design principle of quasi-kinematic support structure was investigated, and advantages of bipod kinematic support were analyzed from the angle of degree of freedom decoupling. Based on structure designed above, the finite element model was established. Taking surface accuracy of the mirror as optimization objectives, the integrated optimization method was adopted to extract the structural parameters with high sensitivity on the surface accuracy in the flexible support structure, and parameters optimization design was carried out. Finally, the static and dynamic characteristics of the optimized mirror assembly were analyzed. The analysis results showed that the surface shape accuracy (RMS) of the mirror assembly is better than 1 nm under a load case of 1g gravity when the optical axis is level. Surface accuracy (RMS) is better than 2 nm under the load case of 4 uniform temperature rise. The first-order natural frequency of the secondary mirror assembly is 587 Hz. The optimized mirror support structure can well unload the additional deformation caused by the support structure, and has good dynamic stiffness, which verifies that the designed mirror and its support structure are reasonable, and the optimization design method is reliable. This paper provides a reference and idea for the design of flexible support structure of space mirror. ? 2019 SPIE.Accession Number: 20200408063347 -
Record 263 of
Title:The design of laser communication terminal test and evaluation station
Author(s):Li, Jing(1); Zhao, Jianke(1); Xue, Xun(1,2,3); Hu, Xinrong(4); Wang, Zhengfeng(1); Kewei, E.(1); Liu, Kai(1)Source: Proceedings of SPIE - The International Society for Optical Engineering Volume: 11052 Issue: DOI: 10.1117/12.2522010 Published: 2019Abstract:Dues to its large capacity of information, super-speed transmission and high stability, laser communication has become a popular kind of satellite communication technology. Different from other kinds of communication technology, laser communication terminals (LCT) consists of optical systems with high imaging quality, high precise and rapid tracking systems. Testing the LCT on land is necessary to ensure its performance on the satellite. This article introduces a LCT-test and evaluation station (LCT-TES) in the laboratory. The LCT-TES is a high quality optical system providing laboratory measurements of the key characteristics of LCT, such as power testing, energy distribution of light spot in the far field, and the angle of beam divergence. The test precision of LCT-TES is also analyzed in this paper. ? 2019 SPIE.Accession Number: 20190806534747 -
Record 264 of
Title:Tracking Algorithm with Correlation Filtering Based on Combination of Adaptive Feature Representation and Fern Classifier
Author(s):Liao, Jiawen(1,2,3); Qi, Chun(1); Cao, Jianzhong(2); Huang, Jijiang(2)Source: Hsi-An Chiao Tung Ta Hsueh/Journal of Xi'an Jiaotong University Volume: 53 Issue: 6 DOI: 10.7652/xjtuxb201906014 Published: June 10, 2019Abstract:A target tracking algorithm based on combination of adaptive feature representation and a fern classifier is proposed to solve the problem that the linear interpolation update strategy used in the tracking algorithms based on kernel correlation filter architecture cannot deal with sudden changes in target's appearance. Firstly, dimension reduction through principal component analysis is carried out for extracted feature layers of the target to obtain good feature layers. Secondly, the target location is determined by combination of the passive-aggressive filters, where the aggressive filter is updated with a fixed update rate in each frame and the passive filter is updated only when a threshold condition is met. The aggressive filter is used to predict the next frame position of the target, and the passive filter is used to calculate the reliability of the predicted position generated by the aggressive filter and detector. When the prediction of the aggressive filter is unreliable, the detector predicts a position of the target. The best prediction of the target position is finally determined by comparing the reliability of both predicted positions. Experiment results show that the proposed method effectively addresses the model corruption and tracking failure caused by target mutation. Results on the OTB2015 dataset show that the proposed method significantly outperforms the discriminative correlation filter with channel and spatial reliability algorithm by 2.78% and 4.26% in precision and area under curve metrics, respectively. ? 2019, Editorial Office of Journal of Xi'an Jiaotong University. All right reserved.Accession Number: 20193507370268