2023

• Record 169 of
  
  Title:Analysis of Detection Capability of Space Target Based on Event Camera
  
  Author(s):Lv, Yuanyuan(1,2,3); Liu, Zhaohui(1,3); Qiao, Wenlong(1,2,3); Zhou, Liang(1,3); Sun, Xiaoxiao(1,2,3); Chen, Peiquan(1,2,3); Li, Wenkai(1,2,3); Zhang, Haiyang(1,2,3)
  Source: Guangzi Xuebao/Acta Photonica Sinica  Volume: 52  Issue: 2  Article Number: 0211001  DOI: 10.3788/gzxb20235202.0211001  Published: February 2023  
  Abstract:Event cameras are increasingly popular in the field of artificial vision systems as a new type of biological vision sensor. Different from traditional detectors，which capture images at a fixed rate，event cameras are inspired by biological retinas and respond asynchronously and independently to changes in the brightness of each pixel in the scene. The pixel unit independently detects the change range of the logarithmic value of the light intensity. When it exceeds the preset threshold，the pixel unit is activated and reads out the relevant information of this activation through an external unit，generally including the position of the pixel，activation time，polarity，and other information. When read out，these information are packaged into a data packet，which is called an"event". After the event is output，the photosensitive pixel unit will return to the inactive state and re-monitor the changes in the outside light intensity. This working principle makes event cameras offer attractive properties compared to traditional cameras：large dynamic range（140 dB vs. 60 dB），high temporal resolution（in the order of µs），low latency，low power consumption，and high pixel bandwidth（in the order of kHz） resulting in reduced motion blur. Hence，Event cameras are widely used in spatial vision problems such as pose estimation，3D reconstruction，and SLAM. With the development of the event camera，it has been gradually applied in the field of space target detection，and has shown great potential. Event cameras provide a new solution for monitoring satellites and stars for space situational awareness. However，there are few research on space situational awareness based on event cameras. Aiming at the problem of space target detection based on event cameras，we clarify the mechanism of event camera for space target observation， and systematically analyze the influencing factors that affect the detection sensitivity of space target based on event camera. Apart from theoretical analysis，we also build a detection sensitivity model of space target based on event cameras. As described by the proposed sensitivity model，the optical system parameters of the observation system，such as the clear aperture of the observation optical system，the diameter of the dispersion spot caused by the optical system，the transmittance of the optical system，the photoelectric conversion capability of the camera，and the atmospheric turbulence，determine the limit observation capability of the system. As the threshold of the event camera increases，the detection sensitivity of the system （characterized by limit magnitude）decreases linearly. Besides，we performed field experiments with telescopes using the CMOS camera and event camera. First，we conducted an experiment to observe the planetary based on the event camera. The observation results show that the event camera can be applied to space target observation. Compared with the traditional CMOS camera，the event camera has a lower spatial resolution，but the characteristics of its low bandwidth communication，low weight，low power，and high speed make it fully meet the harsh requirements of sensors in the aerospace field，and have great application prospects in space target monitoring. In order to explore the impact of the event camera threshold setting on the detection results，we observed Polaris at different thresholds，and the results show that the low threshold makes the signal in the image more obvious but more noise events. When the weak target is observed，the too-low threshold is easy to cause the indistinguishability of noise events and signal events. When the threshold is raised，the detection sensitivity of the system decreases，and the signal is not obvious，which affects the signal recognition. Therefore，when using the event camera for space target observation，the selection of the threshold value is extremely important，not only to ensure high detection sensitivity，but also to avoid the generation of a large number of noise events，which will affect the signal recognition. So establishing a sensitivity model of space target detection based on event camera can provide theoretical guidance for experiments. For the observation system we built，we selected five celestial objects that are easier to distinguish in the sky to calibrate the sensitivity model. The fitting results show good linearity with correlation coefficient greater than 0.95. After that，we chose three other celestial bodies to verify the model. The relative error was less than 3%，so the model we built is accurate. Event cameras are revolutionary sensors that offer many advantages over traditional，frame-based cameras. Their characteristics，such as low latency，low power，high speed and high dynamic range，make event cameras have a large potential for space target detection. In the meantime，many challenges remain ahead. By conducting theoretical analysis and experimental verification，this paper obtains the sensitivity model of space target detection based on event camera. We hope it can provide a few theoretical guidance for space target observation and other related research based on event camera. © 2023 Chinese Optical Society. All rights reserved.
  Accession Number: 20231713945948
• Record 170 of
  
  Title:High sensitivity temperature and humidity sensing based on physically deformed long-period fiber grating
  
  Author(s):Hu, Jiayue(1); Jia, Aochi(1); Li, Menghao(1); Liu, Jihong(1); Ren, Kaili(1,2)
  Source: Proceedings of SPIE - The International Society for Optical Engineering  Volume: 12771  Issue: null  Article Number: 127710M  DOI: 10.1117/12.2689246  Published: 2023  
  Abstract:In this paper, we proposed a highly sensitive temperature and humidity sensors based on two types of physically deformed long-period fiber gratings (LPFGs) which was fabricated by periodically twisting and micro-tapering single-mode fiber, also known as chiral long-period fiber grating (CLPG) and microtapered long-period fiber grating (MTLPFG), respectively. Meanwhile, the superior sensing characteristics of graphene-enhanced CLPG sensor for temperature and polyvinyl alcohol (PVA) coated MTLPFG sensor for humidity are successfully demonstrated. In the temperature experiment, due to the excellent thermal conductivity of graphene, the CLPG transmission spectrum has excellent responsiveness and linearity, and the measured temperature sensitivity is 115 pm/℃. Compared with the traditional fiber gratings, the temperature sensitivity has been significantly improved. Unfortunately, as a humidity measure, fiber grating is insensitive to humidity. Therefore, the MTLPG coated with PVA nanofilms is proposed to realize humidity sensing measurement. Due to the perfect combination of the special micro-nano structure and humidity sensitive film, this humidity sensor obtained excellent sensing sensitivity and linearity. Note that the humidity sensitivity of the PVA-coated MTLPFG has a humidity sensitivity of up to 13.27 pm/%RH. This physically deformed LPFGs are non-degradable, stable and higher sensitive, we believe that it will providing a key role in high-precision temperature and humidity sensing fields. © 2023 SPIE.
  Accession Number: 20240315379594
• Record 171 of
  
  Title:A Micro-Multispectral Vision Sensor: Research on on-line measurement classification and recognition method of coal gangue
  
  Author(s):Guo, Quan(1,2); Liu, Ruqi(3); Wu, Dengshan(1); Yu, Weixing(1)
  Source: Proceedings of SPIE - The International Society for Optical Engineering  Volume: 12962  Issue: null  Article Number: 129620D  DOI: 10.1117/12.3007898  Published: 2023  
  Abstract:Spectral imaging technology based on on-chip splitting provides services for aerospace, industrial and consumer electronics applications. Since each application requires a different set and number of spectral bands, the lack of scalable and high-cost customized splitting schemes hinders the wide application of multispectral imaging. Here, we demonstrate a compact, highly freely customizable imaging spectrometer with initial validation for coal and gangue classification and recognition applications. And the results reflect the potential application of this spectral imaging system in coal and gangue classification and identification. A supervised classification method using support vector machines (SVM) was used to recognize coal and gangue, and the evaluation of classification accuracy shows that more than 82% of the pixels can be correctly classified, and this study provides strong support for the visual sensors with complete spectral band combinations to achieve higher accuracy. © 2023 SPIE. All rights reserved.
  Accession Number: 20240215343580
• Record 172 of
  
  Title:Detail enhancement for infrared image based on Iterative least squares and difference of Gaussian filter
  
  Author(s):Chen, Zhiqiang(1,2,3); Zhao, Zehao(1,2,3); Guan, Lei(1,2,3); Zhou, Feng(1,2,3); Chen, Yaohong(1,3)
  Source: Proceedings of SPIE - The International Society for Optical Engineering  Volume: 12921  Issue: null  Article Number: 1292111  DOI: 10.1117/12.2688130  Published: 2023  
  Abstract:Effective visualization of infrared images with low contrast and low signal-to-noise ratio is one of the key technologies for high-performance infrared imaging systems. The conventional decomposition-based algorithms have advantages in image details enhancement, but still suffer from high computational cost, unbalanced noise suppression and detail information. In this paper, we decompose the base and detail components of the image by the iterative least squares and the Difference of Gaussian filter, and further enhance the base layer and the detail layer via plateau equalization and gradient mask, respectively. We then fusion the enhancement result and re-project to 8-bit dynamic range. Experimental results shown that the proposed method achieves a good balance between detail enhancement and computational cost, with a high-performance in different scenes. © 2023 SPIE.
  Accession Number: 20234815132588
• Record 173 of
  
  Title:A Sparse Sampling Method in the Two-dimensional Spatial Domain for Sheared-beam Imaging Receiving System
  
  Author(s):Chen, Minglai(1,2,3); Ma, Caiwen(1,2,3); Luo, Xiujuan(1,2,3); Liu, Hui(1,2,3); Zhang, Yu(1,3); Yue, Zelin(1,2); Zhao, Jing(1,2)
  Source: Proceedings of SPIE - The International Society for Optical Engineering  Volume: 12601  Issue: null  Article Number: 126010M  DOI: 10.1117/12.2666901  Published: 2023  
  Abstract:In the imaging of low-orbit moving objects, the number of detector elements in the traditional sheared-beam imaging (SBI) system is too great, which seriously restrict the application of SBI. In this paper, the detector array is sparse in two dimensions. We propose a two-dimensional sparse sampling imaging method, which emits a two-dimensional coherent laser array, carries more spectral information of the target at a time and receives speckle echo signals by a two-dimensional sparse detector array for computational imaging. This method can reduce the number of detector elements many times. Firstly, the principle of two-dimensional sparse sampling with SBI detector array is deduced theoretically. Secondly, a two-dimensional spatial sparse reconstruction algorithm is investigated. The target amplitude product and phase difference carried by each detector array element is estimated using discrete Fourier transform, then the target amplitude product and phase difference of all detector array elements are matched respectively to form a complete target amplitude product surface and phase difference surface. The formulas of phase recovery and amplitude demodulation are derived. Finally, the validity and feasibility of the proposed method are verified by simulation. Compared with the traditional three-beam method, when the number of lasers in emission array is M×N, the number of detector elements is reduced to 1/(M-1)/(N-1) of the original without loss of imaging resolution. © 2023 SPIE.
  Accession Number: 20232114125054
• Record 174 of
  
  Title:Investigation of single-shot high-speed photography based on spatial frequency multiplexing
  
  Author(s):Li, Hang(1,2,3); Li, YaHui(1,3); Wang, Xing(1,3); Tian, Jinshou(1,3)
  Source: Journal of the Optical Society of America A: Optics and Image Science, and Vision  Volume: 40  Issue: 3  Article Number: null  DOI: 10.1364/JOSAA.480778  Published: March 2023  
  Abstract:The frequency recognition algorithm for multiple exposures (FRAME) is a spatial frequency multiplexing method that enables high-speed videography with high spatial resolution across a wide field of view and high temporal resolution up to femtoseconds. The criterion to design encoded illumination pulses is an essential factor that affects the sequence depth and reconstruction accuracy of FRAME but was not previously discussed. When the spatial frequency is exceeded, the fringes on digital imaging sensors can become distorted. To exploit the Fourier domain for FRAME with deep sequences and avoid fringe distortion, the maximum Fourier map for sequence arrangement was determined to be a diamond shape. The maximum axial frequency should be a quarter of the sampling frequency of digital imaging sensors. Based on this criterion, the performances of reconstructed frames were theoretically investigated by considering arrangement and filtering methods. To ensure optimal and uniform interframe quality, the frames near the zero frequency should be removed and optimized super-Gaussian filters should be employed. Experiments were conducted flexibly with a digital mirror device to generate illumination fringes. Following these suggestions, the movement of a water drip dropping on a water surface was captured with 20 and 38 frames with uniform interframe quality. The results prove the effectiveness of the proposed methods to improve the reconstruction accuracy and promote the development of FRAME with deep sequences. © 2023 Optica Publishing Group.
  Accession Number: 20231513873233
• Record 175 of
  
  Title:Prior-based collaborative representation with global adaptive weight for hyperspectral anomaly detection
  
  Author(s):Wang, Nan(1,2); Shi, Yuetian(1,2); Cheng, Yinzhu(1,2); Yang, Fanchao(1,3); Zhang, Geng(1,3); Li, Siyuan(1,3); Liu, Xuebin(1,3)
  Source: Journal of Applied Remote Sensing  Volume: 17  Issue: 3  Article Number: 034511  DOI: 10.1117/1.JRS.17.034511  Published: July 1, 2023  
  Abstract:Hyperspectral anomaly detection (HAD) is a technique to find observations without prior knowledge, which is of particular interest as a branch of remote sensing object detection. However, the application of HAD is limited by various challenges, such as high-dimensional data, high intraclass variability, redundant information, and limited samples. To overcome these restrictions, we report an unsupervised strategy to implement HAD by dimensionality reduction (DR) and prior-based collaborative representation with adaptive global salient weight. The proposed framework includes three main steps. First, we select the most discriminating bands as the input hyperspectral images for subsequent processing in a DR manner. Then, we apply piecewise-smooth prior and local salient prior to collaborative representation to produce the initial detection map. Finally, to generate the final detection map, a global adaptive salient map is applied to the initial anomaly map to further highlight anomalies. Most importantly, the experimental results show that the proposed method outperforms alternative detectors on several datasets over different scenes. In particular, on the Gulfport dataset, the area under the curve value obtained by the proposed method is 0.9932, which is higher than the second-best method, convolutional neural network detector, by 0.0071. © 2023 Society of Photo-Optical Instrumentation Engineers (SPIE).
  Accession Number: 20234114853601
• Record 176 of
  
  Title:Recalibrating Features and Regression for Oriented Object Detection
  
  Author(s):Chen, Weining(1,2,3); Miao, Shicheng(1,2); Wang, Guangxing(1,2); Cheng, Gong(1,2)
  Source: Remote Sensing  Volume: 15  Issue: 8  Article Number: 2134  DOI: 10.3390/rs15082134  Published: April 2023  
  Abstract:The objects in remote sensing images are normally densely packed, arbitrarily oriented, and surrounded by complex backgrounds. Great efforts have been devoted to developing oriented object detection models to accommodate such data characteristics. We argue that an effective detection model hinges on three aspects: feature enhancement, feature decoupling for classification and localization, and an appropriate bounding box regression scheme. In this article, we instantiate the three aspects on top of the classical Faster R-CNN, with three novel components proposed. First, we propose a weighted fusion and refinement (WFR) module, which adaptively weighs multi-level features and leverages the attention mechanism to refine the fused features. Second, we decouple the RoI (region of interest) features for the subsequent classification and localization via a lightweight affine transformation-based feature decoupling (ATFD) module. Third, we propose a post-classification regression (PCR) module for generating the desired quadrilateral bounding boxes. Specifically, PCR predicts the precise vertex location on each side of a predicted horizontal box, by simply learning the following: (i) classify the discretized regression range of the vertex, and (ii) revise the vertex location with an offset. We conduct extensive experiments on the DOTA, DIOR-R, and HRSC2016 datasets to evaluate our method. © 2023 by the authors.
  Accession Number: 20231914056478
• Record 177 of
  
  Title:Laser induced spherical bubble dynamics in partially confined geometry with acoustic feedback from container walls
  
  Author(s):Fu, Lei(1,2); Liang, Xiao-Xuan(2); Wang, Sijia(1); Wang, Siqi(3); Wang, Ping(1,4); Zhang, Zhenxi(1); Wang, Jing(1); Vogel, Alfred(2); Yao, Cuiping(1)
  Source: Ultrasonics Sonochemistry  Volume: 101  Issue: null  Article Number: 106664  DOI: 10.1016/j.ultsonch.2023.106664  Published: December 2023  
  Abstract:We investigated laser-induced cavitation dynamics in a small container with elastic thin walls and free or partially confined surface both experimentally and by numerical investigations. The cuvette was only 8–25 times larger than the bubble in its center. The liquid surface was either free, or two thirds were confined by a piston-shaped pressure transducer. Different degrees of confinement were realized by filling the liquid up to the transducer surface or to the top of the cuvette. For reference, some experiments were performed in free liquid. We recorded the bubble dynamics simultaneously by high-speed photography, acoustic measurements, and detection of probe beam scattering. Simultaneous single-shot recording of radius-time curves and oscillation times enabled to perform detailed investigations of the bubble dynamics as a function of bubble size, acoustic feedback from the elastic walls, and degree of surface confinement. The bubble dynamics was numerically simulated using a Rayleigh-Plesset model extended by terms describing the acoustically mediated feedback from the bubble's environment. Bubble oscillations were approximately spherical as long as no secondary cavitation by tensile stress occurred. Bubble expansion was always similar to the dynamics in free liquid, and the environment influenced mainly the collapse phase and subsequent oscillations. For large bubbles, strong confinement led to a slight reduction of maximum bubble size and to a pronounced reduction of the oscillation time, and both effects increased with bubble size. The joint action of breakdown-induced shock wave and bubble expansion excites cuvette wall vibrations, which produce alternating pressure waves that are focused onto the bubble. This results in a prolongation of the collapse phase and an enlargement of the second oscillation, or in time-delayed re-oscillations. The details of the bubble dynamics depend in a complex manner on the degree of surface confinement and on bubble size. Numerical simulations of the first bubble oscillation agreed well with experimental data. They suggest that the alternating rarefaction/compression waves from breakdown-induced wall vibrations cause a prolongation of the first oscillation. By contrast, liquid mass movement in the cuvette corners result in wall vibrations causing late re-oscillations. The strong and rich interaction between the bubble and its surroundings may be relevant for a variety of applications such as intraluminal laser surgery and laser-induced cavitation in microfluidics. © 2023 The Authors
  Accession Number: 20234515022418
• Record 178 of
  
  Title:ViBe algorithm based on background fusion and channel calculation
  
  Author(s):He, Han(1); Zhou, Zuofeng(1); Wu, Qingquan(2)
  Source: Proceedings of SPIE - The International Society for Optical Engineering  Volume: 12748  Issue: null  Article Number: 1274817  DOI: 10.1117/12.2689531  Published: 2023  
  Abstract:ViBe (Visual background extractor) algorithm is a motion target detection algorithm by background modeling, uses domain pixels for background modeling and updates the background model in real time. However, the traditional ViBe algorithm will produce disadvantages such as ghosting and shadow part false detection. This paper solves the problem of ghosting by image fusion mechanism, through the characteristics of the shadow itself, using the shadow part of the three-channel variance value for shadow detection and eliminate the shadow. The experiments show that our algorithm can quickly and effectively solve the ghost and shadow problems in the ViBe algorithm © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
  Accession Number: 20233814739055
• Record 179 of
  
  Title:Precise assembly and adjustment technology of fully free-form surface multi-reflection off-Axis optical system
  
  Author(s):Qin, Xing(1); Fu, Xihong(1,2); Yang, Fan(1); Shen, Zhong(1); Ji, Bindong(1); Zhang, Hongwei(1); Qu, Rui(1)
  Source: Proceedings of SPIE - The International Society for Optical Engineering  Volume: 12976  Issue: null  Article Number: 1297620  DOI: 10.1117/12.3009602  Published: 2023  
  Abstract:With the rapid development of large field of view, large aperture and unobstructed space optical imaging system, the optical imaging system structure has developed from aspherical coaxial and off-Axis free surface off-Axis. Free surface is applied to multi reflective Off-Axis optical system to balance the sharply increased off-Axis aberration. Because the free-form surface does not have symmetry, the full free-form surface multi reflective Off-Axis optical system has lost the rotational symmetry of the traditional optical system in structure, resulting in more degrees of freedom in the installation and adjustment of the full free-form surface multi reflective Off-Axis optical system, the relationship between optical axes of various optical elements is complex, the system integration is more difficult, and the installation and adjustment process is difficult to monitor. Based on this, the paper proposes a precise alignment process method of the full free-form surface multi reflection Off-Axis optical system. The space global coordinate system is established through the space coordinate measurement equipment, and the precise attitude of each reflector is monitored by combining the self-Aligning Theodolite and cube mirror, and the reference transfer space position is measured by using the self-Aligning microscope and the measurement target ball. he engineering project verification shows that this assembly and adjustment process method realizes the unification of the design, processing and assembly and adjustment benchmark of the full free-form surface multi reflection Off-Axis optical system, has strong operability, reduces the difficulty of assembly and integration, and the comprehensive measurement accuracy is better than 0.01 mm. The wave aberration RMS of the final refrigeration relay long wave infrared camera system is better than 0.45 λ @ 632.8nm, meeting the design specifications. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
  Accession Number: 20240315401969
• Record 180 of
  
  Title:Research on the Quantitative Process Technology of Tightening Torque of Optical lens Pressure ring
  
  Author(s):Fu, Xihong(1,2); Kang, Shifa(1); Jia, Xin(1); Li, Shuo(1); Cao, Mingqiang(1); Ji, Bindong(1); Zhao, Yue(1); Shi, Yuanyuan(1)
  Source: Proceedings of SPIE - The International Society for Optical Engineering  Volume: 12507  Issue: null  Article Number: 125071E  DOI: 10.1117/12.2655687  Published: 2023  
  Abstract:The axial compact fixing position of the optical element is mainly carried out in the form of tightening the compression ring in the optical lens assembly process. Most of the existing compression ring tightening methods use forceps and other general press ring tightening tools, the degree of tightening of the pressure ring when used mainly depends on the experience and feel of the assembler, cannot quantify the compression ring tightening torque.In order to solve the above technical problems, the research topic of optical lens compression moment quantification process technology is proposed. Based on the principle of strain sensor, a special digital explicit compression moment device was successfully developed. According to the mass production project of XX optical lenses, the test scheme of the tightening moment of each lens press is designed, and multiple compression ring tightening tests are carried out using a special digital explicit compression moment device, and the corresponding change relationship between the compression moment range of the whole lens and the lens surface type (RMS) is summarized. According to GB/T34516-2017 "Spacecraft Vibration Test Method", the random vibration test method in the vertical direction of "sweep-vibration-sweep frequency" was used to complete the compression moment tightening performance and reliability verification. The test results are shown that the characteristic sweep curve of the optical lens before and after the vibration has not changed, the modality has always remained stable, the lens shape (RMS) remains unchanged, the optical lens is not loosened, the digital explicit compression moment device developed meets the technical requirements of the optical lens assembly process, and the compression ring tightening torque is quantified, which further improves the assembly quality reliability and assembly efficiency. © 2023 SPIE.
  Accession Number: 20230613537950