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Issue 22 ， 2022
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Distortion analysis and focal length testing of off-axis optical system
Abstract：To realize the high-precision distortion analysis and measurement of an off-axis optical system and fast and high-precision distortion correction of on-orbit images， a high-order distortion analysis method is used to fit and analyze the relative distortion of the off-axis optical system. First， the theoretical distortion of the off-axis optical system is examined. Then， the concept of equivalent focal length is proposed， and the relative distortion of the system is fitted and analyzed using the aforementioned analysis method. The distortion testing and focal length measurement are then completed for the well-aligned off-axis optical system. Finally， the measured results are used to complete the object image correspondence of the off-axis optical system. The maximum deviation of the equivalent focal length calculated using the high-order distortion analysis method is 0.366 mm when compared with the results of the ZEMAX ray tracing. The measured focal length deviation of the equivalent coaxial system for an off-axis optical system is only 6.378 mm， and the relative deviation is 0.073%. The correctness and accuracy of this method for distortion analysis and measurement and focal length evaluation of the off-axis optical system are verified， thereby providing reliable input for the fast and high-precision distortion correction of on-orbit images.Keywords：off-axis optical system;Distortion analysis;Focal length testing;Equivalent focal length;High order distortion coefficient- 226
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Published：2022-11-24 -
Analysis of the atmospheric multi-angle polarimetric radiometer for aerial remote sensing and its test experiments
Abstract：The Earth’s atmospheric conditions are closely related to climate change and affect human health and ecological environments. Therefore， atmospheric monitoring is of considerable importance. The polarization sensitivity of atmospheric aerosol scattering radiation provides a new idea for the application of optical polarization remote sensing technology for atmospheric detection. Combining the technical development of China's aerial remote sensing system and the demand for environmental atmospheric remote sensing monitoring， an aerial atmospheric multi-angle polarization detection method is proposed. The key technologies include a cluster polarization optics system design， polarization calibration， etc. The atmospheric multi-angle polarimetric radiometer was developed. First， the polarization detection principle of this radiometer is introduced. Thereafter， the optical system solution design is discussed. The influence of multi-angle detection and calibration accuracy of the radiometer on the posterior error of atmospheric aerosol column concentration retrieval was analyzed. Next， using the standard polarized light generator and the absolute radiometric calibration system， the polarization measurement accuracy of the radiometer was verified， and the absolute radiometric calibration uncertainty was obtained. Next， the special multi-angle and multi-spectral polarization detection data processing system was developed for radiometer airborne remote sensing mode. Finally， the field experimental analysis was conducted. The specifications of the radiometer were verified via aerial flight campaigns and ground-based synchronous observation experiments. The results show that the absolute radiation calibration uncertainty of the radiometer is better than 4%. The polarization measurement error was less than 0.5%， and the aerosol optical thickness retrieval error at the synchronous comparison site was less than 0.05. The polarization data measured by the radiometer can be retrieved to obtain atmospheric aerosol optical thickness and other parameters， which can meet the application requirements of regional environmental atmospheric monitoring.Keywords：aviation;Polarization;remote sensing;multi-angle;radiometer- 84
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Published：2022-11-24 -
Design of 19-core photonic crystal fiber with low loss dispersion compensation in C + L band
Abstract：Dispersion accumulation is a problem experienced in space division multiplexing communication systems that use multi-core fibers. To solve this problem， use of a 19-core photonic crystal fiber （PCF） with low loss dispersion compensation in the C+L band is proposed as multi-core PCFs have flexible and tunable dispersion. The optical properties of the fiber， such as dispersion， inter-core crosstalk （XT）， confinement loss， and bending loss are numerically simulated by the finite element method in combination with coupling mode theory. The results show that the multi-core fiber can significantly suppress XT and confinement loss， while achieving large negative dispersion in the C+L band. The fiber achieves a large negative dispersion of -9 572 ps/nm/km to -13 633 ps/nm/km and a low confinement loss of 2.04×10-5 dB/km to 8.1×10-3 dB/km in the C+L band. At the same time， the XT in the C+L band is between -88.96 dB/100 km and -33.33 dB/100 km， and the bend loss value meets the ITU-T recommendations of G.654 for 19-core PCFs with standard fiber sizes. Therefore， this fiber can play an effective role in dispersion compensation in multi-core fiber communication systems based on space division multiplexing technology.Keywords：space-division multiplex;photonic crystal fiber;multi-core fiber;Dispersion compensation;inter-core crosstalk- 68
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Published：2022-11-24
Modern Applied Optics
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Measurement comparison for class-1 gear involute artifact in China
Abstract：The highest class in the Chinese national standard Gear Involute Artifact GB/T 6467-2010 is class-1， of which the tolerance of profile form deviation for class-1 gear involute artifact is around 1.0 to 2.1 μm， however， the measurement uncertainties of current commercial involute measuring instruments are not sufficient to measure class-1 gear involute artifact. In order to verify the manufacturing accuracy of the gear involute artifact developed by the high-precision gear research laboratory of Dalian University of Technology， Dalian University of Technology， together with the National Institute of Metrology of China， the Northeast National Institute of Metrology of China and the Chongqing Academy of Metrology and Quality Inspection of China， carried out a measurement comparison for a new kind of gear involute artifact with three base circle parameters numbered GIA db100-200-262：06. Based on the measurement results and uncertainties of the base radius and profile form deviation of this gear involute artifact provided by each metrology institute， the reference value of the actual base radius and the profile form deviation is calculated using the weighted average method. The normalized deviation of the measurement results is |En|<1， and the measurement results of each metrology institute are true and valid. Within the 95% confidence interval， the reference values of the four tooth flanks of the gear involutes the gear are ffα=（0.27~0.43）±0.53 μm， which meet the requirements for the tolerance of the profile form deviation and evaluation range of class-1 gear involute artifact according to the Chinese national standard Gear Involute Artifact GB/T 6467-2010.Keywords：gear involute artifact;involute profile deviations;measurement comparison- 148
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Published：2022-11-24 -
Measurement and optimization control of output characteristics of high frequency magnetostrictive transducer
Abstract：The resonance state and output characteristics of high-frequency magnetostrictive transducers are affected by various factors such as electromagnetic excitation conditions， heat generation and load conditions. In order to improve the output performance of high-frequency magnetostrictive transducers， this paper deeply studies the influence regularity with the changing of operating temperature and loads on the resonant frequency and optimal bias magnetic field of the transducer and designs a closed-loop control system. Firstly， according to the transducer impedance circle and output acceleration characteristics， the resonant frequency and the optimal bias magnetic field of the magnetostrictive transducer under different temperatures and loads are experimentally tested to find out their changing rules. Then， based on the test data， a BP neural network prediction model is established and optimized by genetic algorithm and particle swarm optimization algorithm to characterize the nonlinear relationship among temperature， load， resonance frequency and optimal bias current. Finally， the closed-loop control system of magnetostrictive transducer is built and the reference value of the closed-loop controller is adjusted in real time by using the prediction results of the proposed GA-BPNN prediction model to realize the automatic tracking of resonance frequency and optimal bias magnetic field. The experimental results prove that the control system is effective in optimizing the output characteristics of the transducer. The output acceleration amplitude of the transducer can be increased by an average of 25.65% under different working conditions.Keywords：high frequency magnetostrictive transducer;resonant frequency;bias magnetic field;BP neural network;closed-loop control system- 145
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Published：2022-11-24 -
Assembly of countersunk-hole parts based on 3D pose estimation and impedance control
Abstract：For robotic assembly long cylindrical shaft and countersunk-hole parts， this paper investigates the assembly strategies of combining 3D vision， and force perception for compliantly assembling parts in arbitrary positions and poses during assembly. An algorithm is proposed based 3D vision for pose estimation of countersunk-hole parts： firstly， use supervoxel segmentation， Constrained Planar Cuts （CPC）and clustering to complete the preprocessing of point cloud， and then use Weight-based Random Sample Consensus （WRANSAC） plane fitting to acquire plane pose， finally， estimate the assembly position by profile extraction and circle fitting of countersunk-hole. In addition， we implement the compliant assembly of the parts using impedance control. The experimental results indicate that the average distance error ∆d of WRANSAC plane fitting algorithm can be as high as 0.09 mm and the angular error ∆θ can be as high as 1.8°. Moreover， the angular error of the countersunk-hole position in 3D space is 1.0°， which can realize the assembly of parts with a mating clearance of 0.5 mm. The assembly strategy meets the requirements of high precision and compliance of countersunk-hole assembly.Keywords：countersunk-hole parts;compliant assembly;3D pose estimation;impedance control- 175
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Published：2022-11-24
Micro/Nano Technology and Fine Mechanics
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Camera pose estimation based on 2D image and 3D point cloud fusion
Abstract：This paper presents an estimation algorithm for the six degree-of-freedom camera pose obtained from a single RGB image in a specific environment using a combination of the known image and point cloud information. Specifically， we propose a multi-stage camera pose estimation algorithm based on dense scene regression. First， the camera pose estimation dataset is composed by combining the depth image information and Structure from Motion （SFM） algorithm. Then， for the first time， we introduce depth image retrieval into the construction of two- and three-dimensional （2D-3D） matching points. Using the proposed pose optimization function， a multi-stage camera pose estimation method is proposed. The ResNet network considerably improves the pose estimation accuracy. Experimental results indicate that the pose estimation accuracy is 82.7% on average in the open dataset 7 scenes， and 94.8% in our own dataset （estimated poses falling within the threshold of 5 cm/5°）. Compared with other camera pose estimation methods， our method has better pose estimation accuracy for both our and public datasets.Keywords：camera pose estimation;point cloud;feature matching;scene regression- 92
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Published：2022-11-24 -
Multi-regularization image restoration method for X-ray images of integrated circuit
Abstract：The X-ray images of Integrated Circuits （IC） generally have high noise and low contrast characteristics. Considering the different needs in detail preservation and noise removal of edge details and smooth regions， this paper proposes a multi-regularization image restoration method. Firstly， by employing a Fourier transform based Gauss high-pass filter and Gauss low-pass filter， the edge detail and smoothing filter results were obtained as new observed images for image restoration. Then， a TV-l1 mixed regularization model， which takes full use of the advantages of l1 regularization term in detail preservation and Total Variation （TV） regularization term in noise removal， was designed. The model is capable of addressing the problem of excessive smoothing or defective denoising caused by a single regularization term. Experiments on standard and IC X-ray images show that the proposed method can effectively remove noise while retaining more details， laying a foundation for subsequent defect detection of IC.Keywords：image restoration;regularization;Fourier transform- 86
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Published：2022-11-24 -
No-reference video quality objective assessment method based on the content visual perception and transmission distortion
Abstract：This paper proposes a Video Quality Assessment （VQA） method based on video-content perception by analyzing the influence of video content， transmission delay， and encoding and decoding distortion characteristics on the VQA， combined with human visual system characteristics and its mathematical model. In this method， the video contents are described by the texture complexity， local contrast， temporal information of video frame image， and their visual perception. Thus， the video contents perception model can be built， which allows for investigating the influence of the video content and their visual perception on VQA. The relationship between the bit rate and video quality is discussed， whose relationship models are built， to study the impact of the bit rate of video-on-video quality. Subsequently， the VQA model that video quality degradation caused by transmission delay distortion is designed by combining the characteristics of video transmission delay. Finally， the convex optimization method is used to synthesize the above three aspects of models， and a no-reference VQA model considering the video contents， encoding and decoding distortion， transmission delay distortion， and human visual system characteristics， is proposed. The proposed VQA model was tested and verified using the videos from several established video databases and open-source video databases， and its performance was compared with that of 17 existing VQA models. The results showed that the precision Pearson linear and Spearman rank order correlation coefficients of the proposed VQA model reached a minimum of 0.8773 and 0.8336 and a maximum of 0.938 3 and 0.943 8， respectively. This shows that the model has good generalization performance and low complexity. Analyzing the overall efficiency of performance in terms of model accuracy， generalization performance， and complexity， the results show that the proposed model is an excellent VQA model.Keywords：Video Quality Assessment（VQA）;human visual system characteristics;video contents;luminance and chrominance transmission delay- 103
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Published：2022-11-24 -
Coarse-to-fine underwater image enhancement based on multi-level wavelet transform
Abstract：To correct the color distortion and enhance the details of degraded underwater image， this paper proposes a coarse-to-fine underwater image enhancement method based on multi-level wavelet transform. Firstly， a raw underwater image is decomposed into a low-frequency image and a series of high-frequency images based on the wavelet transform. Secondly， a two-stage underwater enhancement network is proposed， which includes a multi-level wavelet transform sub-network and a refinement sub-network with the proposed second-order Runge-Kutta block. The multi-level wavelet transform sub-network， which estimates preliminary result， contains a low-frequency and a high-frequency branch. Specifically， the low-frequency branch treats the color correction problem as the implicit style transfer problem and introduces the instance normalization and the position normalization into the branch. To ensure an accurate reconstruction， when manipulating low-frequency information， the high-frequency branch calculates the enhanced mask according to the information from both low- and high-frequency images and implements the enhancement by multiplying the progressive up-sampling enhanced mask with the high-frequency images. We implemented the inverse wavelet transform and obtain the preliminary results. Finally， the refinement network was designed to further optimize the preliminary results with the proposed second-order Runge-Kutta block. Experimental results demonstrated that the proposed method outperformed the existing methods in enhancement effect on both synthetic and real images， whilst the Peak Signal-to-Noise Ratio （PSNR） improved by 9%. The proposed method also meets the requirement of underwater vision tasks， such as color correction， details enhancement， and clarity.Keywords：underwater optics;wavelet transform;deep learning;color correction;Runge Kutta- 65
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Published：2022-11-24 -
Rapid star pattern matching for precisely tracking telescopes
Abstract：Star pattern matching is critical when using high-precision astronomical positioning technique， which， in turn， is required for the precise determination of space objects’ orbits. This paper proposes a rapid star-pattern-matching method for precisely tracking telescopes， including its principles， program flow and implementation. First， the catalog of pointed sky region was filtered out with the shafting positioning from the encoder； then， after selection and reduction， the stars in the area were compiled into a navigation stars list. After which， the optimized triangle matching method， based on dimension reduction and table look-up methods， was employed in the first frame， where the relation between plate constants verifies the success of matching. The changes of the telescope pointing were considered to calculate the standard coordinates of navigation stars， and the observed stars were matched through the last plate constants. Finally， the coordinates of navigation stars calculated were compared by the plate constants with their reduced values from the catalog， and the position of one space object was calculated through celestial positioning. Experimental results indicated that 39 star pairs could be matched by applying the optimized triangle matching proposed， however， with only approximately 1/300 of the time taken compared to the conventional method. When calculating the following sequential frames （approximately 100 star pairs per-frame）， the matching could be finished in less than 0.04 s. The matched star pairs obtained by the rapid star pattern matching algorithm were used to locate an MEO laser satellite with an average error of approximately 0.5″. As a result， the method proposed fully satisfies the requirements of high accuracy and speed in astronomical positioning for precisely tracking telescopes.Keywords：star pattern matching;astronomical positioning;triangle matching;image sequence;Plate constants- 80
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Published：2022-11-24 -
3D laser point cloud skeleton extraction via balance of local correlation points
Abstract：The shape analysis and shape transformation of the laser-scanning point cloud model depend on the curve skeleton. We proposed a fast and automatic method to obtain the curve skeleton of laser-scanning point cloud to transform the shape of the model and reduce the time consumption caused by manually binding the skeleton. In this method， the initial skeleton point is defined as the midpoint of the nearest correlation point with symmetrical normal in the point cloud. The final skeleton point is obtained by iterating the initial skeleton point to a balance position. Then the principal component analysis method is used to search for the combination of skeleton points that meet the requirements of direction consistency， and the breadth-first search method is used to merge the growing different skeleton branches. Finally， each branch is smoothed and connected by the Laplace smoothing method， a complete skeleton line is obtained and the curve skeleton is used in the task of model shape transformation. The proposed method is compared with the L1-Medial Skeleton， the Mass-driven Topology-aware Curve Skeleton method and other methods， and the original scanned point cloud is used as the test data to verify the effectiveness， robustness， and efficiency. The extraction efficiency of the proposed model is improved to the level that it takes 0.764 s to process the point cloud composed of 8 077 points， and it takes 4.356 s to process a point cloud with 33 041 points. The curve skeleton of laser scanned point cloud extracted is applied to the task of shape transformation of point cloud， which shows the practicability of this method.Keywords：computer vision;point cloud;laser scanning;curve skeleton;PCA;Laplacian smoothing- 73
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Published：2022-11-24
Information Sciences
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