184 results on '"Guang Cai"'
Search Results
2. Motion Compensation/Autofocus in Airborne Synthetic Aperture Radar: A Review
- Author
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Jian Peng, Buge Liang, Hanwen Yu, Jianlai Chen, Mengdao Xing, and Guang-Cai Sun
- Subjects
Physics ,Autofocus ,Synthetic aperture radar ,Motion compensation ,General Computer Science ,law ,General Earth and Planetary Sciences ,Electrical and Electronic Engineering ,Instrumentation ,law.invention ,Remote sensing - Published
- 2022
3. SAR Ground Maneuvering Targets Imaging and Motion Parameters Estimation Based on the Adaptive Polynomial Fourier Transform
- Author
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Yachao Li, Zheng Bao, Dong You, Mengdao Xing, and Guang-Cai Sun
- Subjects
Synthetic aperture radar ,Polynomial ,Computer science ,Interval (mathematics) ,Geotechnical Engineering and Engineering Geology ,Hough transform ,law.invention ,symbols.namesake ,Fourier transform ,law ,Trajectory ,symbols ,Electrical and Electronic Engineering ,Algorithm ,Doppler effect - Abstract
This letter proposes a new method for focusing ground maneuvering targets and estimating the motion parameters with a synthetic aperture radar (SAR) system. In this method, the Hough transform is applied to estimate the cross-track velocity from the slope of the range walk (RW) trajectory, and the RW and Doppler centroid shift are compensated. The second-order Keystone transform is performed to correct the additional range curve caused by the along-track velocity and cross-track acceleration. Then, we adopt the adaptive polynomial Fourier transform to estimate the second- and third-order Doppler parameters from a 1-D parameter interval, and the corresponding motion parameters are calculated. Finally, the moving target is well focused after the motion parameters compensation because the second- and third-order Doppler parameters are efficiently eliminated. Both the simulated and real data processing results are presented to demonstrate the validity of the proposed algorithm.
- Published
- 2022
4. A Real-Time Unified Focusing Algorithm (RT-UFA) for Multi-Mode SAR via Azimuth Sub-Aperture Complex-Valued Image Combining and Scaling
- Author
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Yanbin Liu, Zheng Bao, Min Bao, Guang-Cai Sun, Shiyu Wang, Mengdao Xing, and Jun Yang
- Subjects
Azimuth ,Synthetic aperture radar ,Pixel ,Aperture ,Cascade ,Computer science ,Mode (statistics) ,General Earth and Planetary Sciences ,Electrical and Electronic Engineering ,Focus (optics) ,Scaling ,Algorithm - Abstract
Spaceborne synthetic aperture radar (SAR) can operate at various modes, including stripmap mode, spotlight mode, sliding spotlight mode, and Terrain observation by progressive scans (TOPS) mode. These four imaging modes can be regarded as unified, differing in rotation-center ranges. To uniformly focus the data of these four imaging modes in real-time, this article proposes a real-time unified focusing algorithm (RT-UFA) for the multi-mode SAR via azimuth sub-aperture complex-valued image combining and scaling. The imaging processing can be performed while the data are being recorded. In the first stage of imaging, sub-aperture complex-valued images with relative low-resolution can be obtained by the cascade of the extended chirp scaling (ECS) and azimuth dechirp. Then, these complex-valued images are coherently combined by shifting the integer number of pixels, and thus the full-resolution image of all the recorded data can be obtained. The azimuth scaling and the pixels shifting in the RT-UFA are analyzed in detail. Simulation and SAR data results are presented to validate the analysis and RT-UFA.
- Published
- 2022
5. EFTL: Complex Convolutional Networks With Electromagnetic Feature Transfer Learning for SAR Target Recognition
- Author
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Mengdao Xing, Guang-Cai Sun, Hanwen Yu, and Jiaming Liu
- Subjects
Synthetic aperture radar ,Signal processing ,Artificial neural network ,business.industry ,Computer science ,Activation function ,ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION ,Initialization ,Pattern recognition ,Graph drawing ,Feature (machine learning) ,General Earth and Planetary Sciences ,Artificial intelligence ,Electrical and Electronic Engineering ,Transfer of learning ,business - Abstract
Considering that synthetic aperture radar (SAR) images obtained directly after signal processing are in the form of complex matrices, we propose a complex convolutional network for SAR target recognition. In this article, we give a brief introduction to complex convolutional networks and compare them with the real counterpart. A complex activation function is applied to analyze the influence of phase information in complex neural networks. Inspired by the theory of network visualization, a special kind of transfer learning based on the electromagnetic property from the attributed scattering center model is applied in our networks to modulate the first convolutional layer. The experiment shows a better performance in terms of classification accuracy compared to random weight initialization.
- Published
- 2022
6. Integrating the Reconstructed Scattering Center Feature Maps With Deep CNN Feature Maps for Automatic SAR Target Recognition
- Author
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Guang-Cai Sun, Zheng Bao, Jinsong Zhang, and Mengdao Xing
- Subjects
Synthetic aperture radar ,business.industry ,Computer science ,Feature extraction ,ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION ,Pattern recognition ,Geotechnical Engineering and Engineering Geology ,Convolutional neural network ,Weighting ,Automatic target recognition ,Feature (computer vision) ,Artificial intelligence ,Electrical and Electronic Engineering ,business ,Block (data storage) - Abstract
Automatic target recognition has been one of the hottest research in synthetic aperture radar (SAR) data processing. Noticing that popular recognition methods cannot utilize multiple features of SAR complex data, a method fused scattering center feature and deep convolutional neural network (CNN) feature is proposed in this letter. This method contains three key parts, namely, scattering center extraction and reconstruction block, CNN feature extraction block, and final feature fusion and classification block. In this process, the scattering center feature and CNN feature are fused at the level of feature maps, which retain the space information of 2-D feature maps. What is more, the proposed half end-to-end strategy realizes the automatic update of weighting parameters in feature extraction network and subnetwork, which promotes a better recognition efficiency. Experimental results on measured SAR data show that the proposed method can achieve better accuracy than other single feature-based methods and feature fusion methods.
- Published
- 2022
7. A Postmatched-Filtering Image-Domain Subspace Method for Channel Mismatch Estimation of Multiple Azimuth Channels SAR
- Author
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Zijing Zhang, Jixiang Xiang, Yong Wang, Mengdao Xing, Jun Yang, Zheng Bao, Min Bao, and Guang-Cai Sun
- Subjects
Synthetic aperture radar ,Image domain ,Azimuth ,Computer science ,Signal reconstruction ,General Earth and Planetary Sciences ,Filter (signal processing) ,Electrical and Electronic Engineering ,Algorithm ,Subspace topology ,Computer Science::Information Theory ,Communication channel - Abstract
Multiple azimuth channels (MACs) synthetic aperture radar (SAR) can theoretically achieve high azimuth resolution and wide swath (HRWS). Nevertheless, in practice, channel mismatch will lead to ghost or azimuth ambiguities, which will degrade the imaging quality. This article proposes a novel idea for estimating the channel mismatch of MACs SAR in the image domain. First, we found that the degree of freedom (DOF) of MACs signals doubles after signal reconstruction and imaging. As a result, when the channel number is not great enough, the subspace method for error estimation is unable to be implemented. To deal with this problem, we introduce a DOF compression method based on spectral filtering. This method can decrease the image-domain DOF. Finally, an image-domain subspace method is proposed to estimate the channel phase error, using the focused data and selecting the high SNR region of SAR images. The proposed method has advantages for the channel phase error estimation. Simulated space-borne MACs SAR data and real measured airborne SAR data are processed to demonstrate the effectiveness of the proposed method.
- Published
- 2022
8. Multiple Statistics Contributing to Few-Sample Deep Learning for Subtle Trace Detection in High-Resolution SAR Images
- Author
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Jinsong Zhang, Guang-Cai Sun, Mengdao Xing, and Zhihao Wang
- Subjects
Synthetic aperture radar ,Pixel ,business.industry ,Computer science ,Deep learning ,ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION ,Estimator ,Inductive transfer ,Statistics ,General Earth and Planetary Sciences ,Artificial intelligence ,False alarm ,Electrical and Electronic Engineering ,business ,Change detection ,TRACE (psycholinguistics) - Abstract
With the ability to locate subtle trace objects in the large-scale region, coherent change detection (CCD) has been vital research for a synthetic aperture radar (SAR) system. Finding the difference between repeat-pass repeat-geometry SAR image pair and extracting impressive trace pixels from difference image, the SAR CCD methods consist of a difference generation module and a difference analysis module. The previous CCD methods mainly pay attention to devising a sophisticated working system or an appropriate statistic model to generalize a well difference image. In this article, we introduce the deep learning method into the CCD algorithm and propose a novel trace detection paradigm, which works by hierarchically fusing the unsupervised coherent statistics model and supervised deep learning model. To be specific, the complex reflectance change detection estimator is introduced to generate a difference image and reduce the false alarm in the low clutter-to-noise region. Since the low correlation in a difference image caused by the natural factors severely affects the detection performance, the multiple statistics based on intensity summation and intensity difference are, respectively, proposed to extract water region and vegetation region and suppress the corresponding false alarm. Then the construction of the coarse-to-fine image makes use of land cover information and trace features while the compressed Unet improves the utilization efficiency of trace samples. Meanwhile, the inductive transfer learning based on unsupervised pretraining and few labeled trace samples helps to train a well detection model. Experiments on measured SAR data demonstrate the effectiveness of proposed methods.
- Published
- 2022
9. Oriented Gaussian Function-Based Box Boundary-Aware Vectors for Oriented Ship Detection in Multiresolution SAR Imagery
- Author
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Mengdao Xing, Jinsong Zhang, Ning Li, and Guang-Cai Sun
- Subjects
Synthetic aperture radar ,Pixel ,Computer science ,business.industry ,Deep learning ,ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION ,Convolutional neural network ,Feature (computer vision) ,Robustness (computer science) ,Minimum bounding box ,General Earth and Planetary Sciences ,Computer vision ,Pyramid (image processing) ,Artificial intelligence ,Electrical and Electronic Engineering ,business ,GeneralLiterature_REFERENCE(e.g.,dictionaries,encyclopedias,glossaries) - Abstract
As an important remote sensing means, synthetic aperture radar (SAR) has many superiorities to other sensors. How to effectively detect and locate ships in SAR images is also a popular field. In previous ship detection research, most algorithms focus on detecting the horizontal bounding box of ship targets, which ignore the rotation angle of each ships. Thus, too much background noise in the horizontal detection results makes them difficult to describe each ship accurately. Inspired by the powerful feature representation ability of convolutional neural networks (CNNs), a novel anchor-free and keypoint-based deep learning method is proposed for oriented ship detection in multiresolution SAR images. Our detector first extracts multilevel features from the input SAR image with a backbone network and feature pyramid network. Next, considering multiscale ships in multiresolution SAR images, we detect different sizes of ships on different levels of feature maps with identical head network structures. In each head network, the classification subnetwork determines each pixel in feature maps as the central pixel of this ship or not, and the regression subnetwork regresses the oriented bounding box for each ship. In the training process, the proposed oriented nonnormalized Gaussian function is used to describe the center point of ship targets, while the nonuniform weighting of the different level loss functions is used to suppress the imbalanced sample distribution. Experimental results on two authoritative SAR-oriented ship detection datasets and two Gaofen-3 images demonstrate the effectiveness and robustness of the proposed methods.
- Published
- 2022
10. A Fast Cartesian Back-Projection Algorithm Based on Ground Surface Grid for GEO SAR Focusing
- Author
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Xiaoxiang Chen, Wenkang Liu, Mengdao Xing, Guang-Cai Sun, Quan Chen, and Liang Han
- Subjects
Synthetic aperture radar ,Image fusion ,Computational complexity theory ,Computer science ,ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION ,Grid ,law.invention ,Azimuth ,Aliasing ,law ,Orbit (dynamics) ,General Earth and Planetary Sciences ,Cartesian coordinate system ,Electrical and Electronic Engineering ,Algorithm - Abstract
Geosynchronous-earth-orbit (GEO) SAR provides excellent continuous observing capability and large swath. How-ever, the extremely long synthetic aperture time, the curved orbit and the nonplanar ground surface cause serious spatial variance in the GEO SAR signal. In this paper, a novel fast Cartesian Back Projection (BP) algorithm based on sub-aperture imaging on ground and multi-stage fusion is proposed for accurately and efficiently imaging of GEO SAR. The imaging grids are arranged on the ground surface to avoid the azimuth defocusing caused by flat-ground-approximation. Then, a new two-step spectrum compression method is derived to solve the spectrum aliasing of sub-aperture images. And a multi-stage image fusion method is adopted to combine all the sub-aperture images with high efficiency. The computational complexity and the approximation of the proposed algorithm are also discussed. Simulation results verify the effectiveness of the proposed algorithm.
- Published
- 2022
11. 2-D Frequency Autofocus for Squint Spotlight SAR Imaging With Extended Omega-K
- Author
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Hao Lin, Dong You, Guang-Cai Sun, Xiaoxiang Chen, Jianlai Chen, and Mengdao Xing
- Subjects
Synthetic aperture radar ,Autofocus ,Computer science ,business.industry ,Phase (waves) ,Computer Science::Software Engineering ,Division (mathematics) ,law.invention ,Azimuth ,law ,Motion error ,General Earth and Planetary Sciences ,Preprocessor ,Computer vision ,Artificial intelligence ,Electrical and Electronic Engineering ,business - Abstract
In the existing time-domain autofocus algorithms, the azimuth deramping operation will change the azimuth-independent phase into the azimuth-dependent phase, which may greatly reduce the accuracy of autofocus processing in squint spotlight synthetic aperture radar (SAR). In contrast, the frequency-domain autofocus algorithms can avoid this problem because it does not involve the azimuth deramping operation. However, the existing frequency-domain autofocus algorithms are proposed based on the assumption of broadside mode, which cannot be directly applied to the squint mode. Therefore, this article extends the existing frequency-domain autofocus algorithm to the squint mode combined with the extended Omega-K (EOK) algorithm. Furthermore, a space division (SD) algorithm is embedded into the proposed algorithm as preprocessing, which can effectively compensate for the azimuth-dependent motion error. The simulation and real data are processed to verify the effectiveness of the algorithm.
- Published
- 2022
12. Moving Target Radial Velocity Estimation Method for HRWS SAR System Based on Subspace Projection
- Author
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Xiaoxiang Chen, Guang-Cai Sun, Zheng Bao, Dong You, Boyu Li, and Mengdao Xing
- Subjects
Synthetic aperture radar ,Computer science ,business.industry ,Azimuth direction ,Geotechnical Engineering and Engineering Geology ,Moving target indication ,Azimuth ,Radial velocity ,Position (vector) ,Computer vision ,Artificial intelligence ,Electrical and Electronic Engineering ,Projection (set theory) ,business ,Subspace topology - Abstract
High-resolution wide-swath (HRWS) multichannel synthetic aperture radar (SAR) system possesses a number of receiving channels along the azimuth direction, so it has the capacity of moving target indication and imaging. However, due to the radial velocity of the moving target, false targets occur in the focused image. By estimating the radial velocity and combining it with moving target imaging, false targets can be effectively suppressed. In this letter, a method of radial velocity estimation of a moving target is proposed based on the theory of subspace projection. This method does not need to estimate the real azimuth position of the moving target and can predict the processing time. Simulation and airborne measured data show the effectiveness of the proposed method.
- Published
- 2022
13. Azimuth Variant Motion Error Compensation Algorithm for Airborne SAR Imaging Based on Doppler Adjustment
- Author
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Xiaoxiang Chen, Minghui Wan, Mengdao Xing, and Guang-Cai Sun
- Subjects
Synthetic aperture radar ,Motion compensation ,business.industry ,Computer science ,Geotechnical Engineering and Engineering Geology ,Compensation algorithm ,Image (mathematics) ,Azimuth ,symbols.namesake ,symbols ,Motion error ,Computer vision ,Artificial intelligence ,Electrical and Electronic Engineering ,business ,Doppler effect ,Scaling - Abstract
Conventional beam-center approximation-based motion compensation (MOCO) algorithms fail to achieve an optimally focused image in the case of the high-resolution and high-frequency (HRHF) synthetic aperture radar (SAR) system. In this letter, a novel MOCO algorithm based on Doppler adjustment is developed with the ability to compensate the azimuth variant motion error. The change of the Doppler spectrum caused by the azimuth variant motion error is investigated and is eliminated by Doppler scaling. The proposed MOCO algorithm has dramatically improved precision when compared with the conventional MOCO methods in HRHF SAR imaging. Simulation experiments and extensive comparisons with other MOCO algorithms verify the effectiveness of the proposed algorithm.
- Published
- 2022
14. Ground Cartesian Back-Projection Algorithm for High Squint Diving TOPS SAR Imaging
- Author
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Xiaoxiang Chen, Jun Yang, Boyu Li, Guang-Cai Sun, Mengdao Xing, and Zheng Bao
- Subjects
Synthetic aperture radar ,Data processing ,Computer science ,law.invention ,Azimuth ,Aliasing ,law ,Frequency domain ,General Earth and Planetary Sciences ,Cartesian coordinate system ,Electrical and Electronic Engineering ,Algorithm ,Interpolation ,Ground plane - Abstract
This article presents a fast back-projection (BP) algorithm based on subaperture (SA) image coherent combination in a downsampled Cartesian coordinate grid for high squint diving terrain observation by progressive scans (HSD-TOPS) synthetic aperture radar (SAR) ground plane imaging. A two-step spectrum compression (SC) method is proposed to coherently combine the aliasing SA images by exploiting the relationship between the wavenumber and the image frequency. The first-step SC is introduced to align the spectrum support region centers. The second-step SC effectively corrects the space-variant spectrum inclination. The proposed algorithm does not need interpolation in the process of image combination, which ensures the accuracy and the efficiency of the algorithm. Furthermore, the SC method is well-modified to suppress the sidelobes of the focused image. Simulation and measured data processing verify the effectiveness of the proposed method.
- Published
- 2021
15. 2-D Beam Steering Method for Squinted High-Orbit SAR Imaging
- Author
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Wenkang Liu, Vito Pascazio, Zheng Bao, Mengdao Xing, Guang-Cai Sun, and Quan Chen
- Subjects
Synthetic aperture radar ,Physics ,squint ,swath maximation ,business.industry ,Beam steering ,2-D beam steering (TDBS), high-orbit synthetic aperture radar (SAR), resolution adjustment, squint, swath maximation ,0211 other engineering and technologies ,resolution adjustment ,02 engineering and technology ,High Earth orbit ,Azimuth ,Optics ,2-D beam steering (TDBS) ,Orbit (dynamics) ,General Earth and Planetary Sciences ,high-orbit synthetic aperture radar (SAR) ,Electrical and Electronic Engineering ,Antenna (radio) ,business ,Image resolution ,Beam (structure) ,021101 geological & geomatics engineering - Abstract
Since path curvature becomes severer for higher orbit synthetic aperture radar (SAR), the stripmap mode may not provide a reliable azimuth resolution under different look angles or at different positions. Beam steering is especially valuable herein for adjusting the azimuth resolution under different observation conditions by designing the antenna steering rate. Moreover, considering that the large range migration and center range variation in the squint mode may increase the echo length and reduce the achievable scene width, we proposed a novel 2-D beam steering (TDBS) method, which promises not only a required azimuth resolution but also a wide swath (or shortened echo length) at squint when cooperated with the variable interpulse time (VIPT) technique. The simulation results obtained under different look directions are shown to validate the effectiveness of the proposed beam controlling method.
- Published
- 2021
16. Water Body Detection in High-Resolution SAR Images With Cascaded Fully-Convolutional Network and Variable Focal Loss
- Author
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Yihua Hu, Li Mengya, Jianlai Chen, Zheng Bao, Guang-Cai Sun, Jinsong Zhang, and Mengdao Xing
- Subjects
Conditional random field ,Synthetic aperture radar ,Pixel ,Computer science ,business.industry ,Scattering ,Gaussian ,Feature extraction ,0211 other engineering and technologies ,Pattern recognition ,02 engineering and technology ,Convolutional neural network ,Upsampling ,symbols.namesake ,Robustness (computer science) ,symbols ,General Earth and Planetary Sciences ,Artificial intelligence ,Graphical model ,Pyramid (image processing) ,Electrical and Electronic Engineering ,business ,021101 geological & geomatics engineering - Abstract
The water body detection in high-resolution synthetic aperture radar (SAR) images is a challenging task due to the changing interference caused by multiple imaging conditions and complex land backgrounds. Inspired by the excellent adaptability of deep neural networks (DNNs) and the structured modeling capabilities of probabilistic graphical models, the cascaded fully-convolutional network (CFCN) is proposed to improve the performance of water body detection in high-resolution SAR images. First, for the resolution loss caused by convolutions with large stride in traditional convolutional neural network (CNN), the fully-convolutional upsampling pyramid networks (UPNs) are proposed to suppress this loss and realize pixel-wise water body detection. Then considering blurred water boundary, the fully-convolutional conditional random fields (FC-CRFs) are introduced to UPNs, which reduce computational complexity and lead to the automatic learning of Gaussian kernels in CRFs and the higher boundary accuracy. Furthermore, to eliminate the inefficient training caused by imbalanced categorical distribution in the training data set, a novel variable focal loss (VFL) function is proposed, which replaces the constant weighting factor of focal loss with the frequency-dependent factor. The proposed methods can not only improve the pixel accuracy and boundary accuracy but also perform well in detection robustness and speed. Results of GaoFen-3 SAR images are presented to validate the proposed approaches.
- Published
- 2021
17. Fast Rotation Matching Method for SAR and Optical Images
- Author
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Tao Xiong, Xinchen Li, Liang Han, Yachao Li, Mengdao Xing, Liang Guo, and Guang-Cai Sun
- Subjects
Synthetic aperture radar ,Atmospheric Science ,Matching (graph theory) ,Computer science ,Fast Fourier transform ,Geophysics. Cosmic physics ,Directional derivative ,rotation matching ,optical image ,Histogram ,Computer vision ,Computers in Earth Sciences ,Adaptive optics ,TC1501-1800 ,Cross-correlation ,business.industry ,QC801-809 ,fungi ,synthetic aperture radar (SAR) ,body regions ,Ocean engineering ,Computer Science::Computer Vision and Pattern Recognition ,Artificial intelligence ,business ,Rotation (mathematics) - Abstract
The rotation matching between synthetic aperture radar (SAR) and optical images is essential for their registration. In this article, we introduce a novel fast rotation matching method for SAR and optical images. In the method, the absolute directional derivative histograms (ADDHs) of SAR and optical images can be used to reflect the rotation difference between them, and then the rotation difference is removed by the cross correlation of the two images’ ADDHs. Subsequently, we generate the ADDHs by oriented Gaussian-Gamma-shaped operator. Then, the cross correlation based on fast Fourier transform is used to deal with the ADDHs of SAR and optical images in order to determine the rotation difference of the two images. The experiment results demonstrate that the proposed method can detect the rotation difference in various conditions and achieves rotation matching with high speed.
- Published
- 2021
18. A High-Squint TOPS SAR Imaging Algorithm for Maneuvering Platforms Based on Joint Time-Doppler Deramp Without Subaperture
- Author
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Zheng Bao, Ning Li, Bowen Bie, Mengdao Xing, and Guang-Cai Sun
- Subjects
Synthetic aperture radar ,Computer science ,business.industry ,Beam steering ,0211 other engineering and technologies ,02 engineering and technology ,Geotechnical Engineering and Engineering Geology ,Signal ,Time–frequency analysis ,symbols.namesake ,Aliasing ,symbols ,Computer vision ,Time domain ,Artificial intelligence ,Electrical and Electronic Engineering ,business ,Doppler effect ,021101 geological & geomatics engineering - Abstract
The beam steering of high-squint terrain observation by progressive scans (TOPS) synthetic aperture radar (SAR) mounted on maneuvering platforms causes azimuth spectrum aliasing and nonlinear variation of the Doppler center with target azimuth position. A joint time-Doppler deramp (JTDD) based method is proposed and mainly contains two parts. First, for the azimuth spectrum aliasing, the unfolded 2-D spectrum is obtained by a modified linear deramp function in the azimuth time domain constructed from the 3-D motion parameters. After range cell migration correction (RCMC), the data supporting area in the azimuth time domain is expanded, and thus, aliased because of the nonlinear variation of Doppler center. Then, a nonlinear deramp operation in the Doppler domain is further proposed to obtain a nonaliasing signal. The proposed algorithm is efficient with less zero-padding due to the consideration of nonlinear components of Doppler center variation. Simulation and real SAR data processing are presented to validate the proposed algorithm.
- Published
- 2020
19. Clutter Suppression via Subspace Projection for Spaceborne HRWS Multichannel SAR System
- Author
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Boyu Li, Yihua Hu, Liang Guo, Guang-Cai Sun, Zheng Bao, and Mengdao Xing
- Subjects
Synthetic aperture radar ,Pulse repetition frequency ,Covariance matrix ,Computer science ,business.industry ,0211 other engineering and technologies ,02 engineering and technology ,Geotechnical Engineering and Engineering Geology ,symbols.namesake ,symbols ,Clutter ,Computer vision ,Artificial intelligence ,Nyquist frequency ,Electrical and Electronic Engineering ,business ,Projection (set theory) ,Doppler effect ,Subspace topology ,021101 geological & geomatics engineering - Abstract
Traditional clutter suppression methods are mainly studied under the condition that the pulse repetition frequency (PRF) of the system is not less than the Nyquist frequency. Whereas in the high-resolution and wide-swath (HRWS) multichannel synthetic aperture radar (SAR) system, a low PRF is used to break through the minimum antenna area constraint. The low PRF case brings new challenges to the traditional clutter suppression methods. In this letter, a subspace projection clutter suppression method is proposed based on the fact that moving targets and the clutter consist in different signal subspaces. This method can be directly applied to the HRWS multichannel SAR system, and it shows better performance compared to the space-time adaptive processing (STAP) when the moving target components cannot be ignored in the clutter covariance matrix calculation. Simulated data and airborne measured data are processed to verify its effectiveness.
- Published
- 2020
20. Focusing of MEO SAR Data Based on Principle of Optimal Imaging Coordinate System
- Author
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Wenkang Liu, Zheng Bao, Mengdao Xing, Hang Li, and Guang-Cai Sun
- Subjects
Synthetic aperture radar ,Image formation ,Computer science ,Coordinate system ,0211 other engineering and technologies ,02 engineering and technology ,Signal ,symbols.namesake ,Linearization ,symbols ,General Earth and Planetary Sciences ,Electrical and Electronic Engineering ,Algorithm ,Doppler effect ,021101 geological & geomatics engineering - Abstract
The curved trajectory and long synthetic aperture time of medium-Earth-orbit (MEO) synthetic aperture radar (SAR) lead to a 2-D spatial variation in the signals. Traditional methods treat the range and azimuth variations separately and usually suffer from high computational complexities. In this article, we investigate the Doppler rate distribution across a large scene and exploit an optimal imaging coordinate system, in which the MEO SAR signals satisfy the azimuth-shift-invariant property. Thus, the additional processing of the azimuth spatial variation in MEO SAR imaging algorithms can be avoided, and the efficiency of the image formation processor can be obviously improved. The Doppler linearization is used to address the higher-order Doppler parameters to achieve more precise focusing, and at the same time, addresses the azimuth time shift caused by the changes of signal distribution. Finally, processing results of simulated stripmap-mode data with the 2-m resolution are presented to validate the proposed algorithm.
- Published
- 2020
21. GF-3 data real-time processing method based on multi-satellite distributed data processing system
- Author
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Jun Yang, Liang Guo, Mengdao Xing, Yandong Cao, and Guang-Cai Sun
- Subjects
Synthetic aperture radar ,Data processing ,Computer science ,Real-time computing ,0211 other engineering and technologies ,Metals and Alloys ,General Engineering ,Process (computing) ,020206 networking & telecommunications ,02 engineering and technology ,Data processing system ,Kernel (image processing) ,0202 electrical engineering, electronic engineering, information engineering ,Satellite ,Raw data ,Field-programmable gate array ,021101 geological & geomatics engineering - Abstract
Due to the limited scenes that synthetic aperture radar (SAR) satellites can detect, the full-track utilization rate is not high. Because of the computing and storage limitation of one satellite, it is difficult to process large amounts of data of spacebome synthetic aperture radars. It is proposed to use a new method of networked satellite data processing for improving the efficiency of data processing. A multi-satellite distributed SAR real-time processing method based on Chirp Scaling (CS) imaging algorithm is studied in this paper, and a distributed data processing system is built with field programmable gate array (FPGA) chips as the kernel. Different from the traditional CS algorithm processing, the system divides data processing into three stages. The computing tasks are reasonably allocated to different data processing units (i.e., satellites) in each stage. The method effectively saves computing and storage resources of satellites, improves the utilization rate of a single satellite, and shortens the data processing time. Gaofen-3 (GF-3) satellite SAR raw data is processed by the system, with the performance of the method verified.
- Published
- 2020
22. Design of synthetic aperture radar low-intercept radio frequency stealth
- Author
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Wensheng Chang, Yanbin Liu, Guang-Cai Sun, and Haihong Tao
- Subjects
Synthetic aperture radar ,Radio frequency ,Geology ,Remote sensing - Published
- 2020
23. Highly Squinted MEO SAR Focusing Based on Extended Omega-K Algorithm and Modified Joint Time and Doppler Resampling
- Author
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Xiang-Gen Xia, Guang-Cai Sun, Mengdao Xing, Zheng Bao, Dong You, and Wenkang Liu
- Subjects
Synthetic aperture radar ,Time delay and integration ,symbols.namesake ,Computer science ,Resampling ,Bandwidth (signal processing) ,symbols ,General Earth and Planetary Sciences ,Wavenumber ,Electrical and Electronic Engineering ,Algorithm ,Doppler effect - Abstract
A squinted observation geometry along with long integration time significantly aggravates the range walk and spatial variation of a medium-earth-orbit (MEO) synthetic aperture radar (SAR) signal. Variable pulse repeating frequency (PRF) is recommended to avoid the blockage in echo recording and save storage space. The existing wavenumber algorithms cannot handle the nonlinear and range–azimuth-coupled spatial variation (RACSP) over a large scene. In this paper, we propose a modified Stolt mapping method along with a modified joint time and Doppler resampling (JTDR) for highly squinted MEO SAR data processing. An azimuth timescale transformation is used to deal with the nonlinear spatial variation of the azimuth frequency-modulation (FM) rate. An extended Omega-K is used to linearize the range frequency and achieve range cell migration correction (RCMC). To address the RACSP, the Doppler is linearized in the range-Doppler domain using a range-dependent Doppler scale transformation. The computational complexity and geometry distortion correction (GDC) are also discussed. Simulation results are shown to verify the effectiveness of the developed focusing approaches.
- Published
- 2019
24. Ship Imaging based on Azimuth Ambiguity Resolving for High-Speed Maneuvering Platforms Sar with Small-Aperture
- Author
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Mengdao Xing, Ning Li, Guang-Cai Sun, and Vito Pascazio
- Subjects
Synthetic aperture radar ,Computer science ,business.industry ,media_common.quotation_subject ,ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION ,Ambiguity ,Residual ,Azimuth ,symbols.namesake ,symbols ,ComputerSystemsOrganization_SPECIAL-PURPOSEANDAPPLICATION-BASEDSYSTEMS ,Computer vision ,Artificial intelligence ,Envelope (radar) ,Antenna (radio) ,business ,Image resolution ,Doppler effect ,media_common - Abstract
Due to the constraint of minimum antenna area, azimuth ambiguity resolving is a challenging task in the ship focusing for single-channel synthetic aperture radar (SAR) mounted on high-speed maneuvering platforms. In order to accommodate the issues, a ship focusing algorithm based on azimuth ambiguity resolving is proposed in this paper. For ship SAR imaging with small-aperture data, the energies of different targets are separated in Doppler domain with different Doppler ambiguity numbers. Thus, the Doppler ambiguity number of a single target can be estimated by residual envelope inclination. Then, the target can be accurately focused and located at the correct position by the known Doppler ambiguity number. After the operation of each target is completed, the focusing SAR image of the whole scene can be obtained. Finally, simulation results are presented to validate the proposed algorithm.
- Published
- 2021
25. Refocusing of Moving Ships in Squint SAR Images Based on Spectrum Orthogonalization
- Author
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Liang Han, Min Bao, Xuyao Tong, Yu Zhang, Guang-Cai Sun, and Mengdao Xing
- Subjects
Synthetic aperture radar ,Motion compensation ,Computational complexity theory ,Computer science ,spectrum orthogonalization ,squint minimization ,Science ,010401 analytical chemistry ,Fast Fourier transform ,0211 other engineering and technologies ,02 engineering and technology ,Translation (geometry) ,01 natural sciences ,0104 chemical sciences ,squint synthetic aperture radar (SAR) ,General Earth and Planetary Sciences ,back-projection (BP) algorithm ,moving ship refocusing ,Orthogonalization ,Algorithm ,021101 geological & geomatics engineering ,Analytic function ,Interpolation - Abstract
Moving ship refocusing is challenging because the target motion parameters are unknown. Moreover, moving ships in squint synthetic aperture radar (SAR) images obtained by the back-projection (BP) algorithm usually suffer from geometric deformation and spectrum winding. Therefore, a spectrum-orthogonalization algorithm that refocuses moving ships in squint SAR images is presented. First, “squint minimization” is introduced to correct the spectrum by two spectrum compression functions: one to align the spectrum centers and another to translate the inclined spectrum into orthogonalized form. Then, the precise analytic function of the two-dimensional (2D) wavenumber spectrum is derived to obtain the phase error. Finally, motion compensation is performed in the two-dimensional wavenumber domain after the motion parameter is estimated by maximizing the image sharpness. This method has low computational complexity because it lacks interpolation and can be implemented by the inverse fast Fourier translation (IFFT) and fast Fourier translation (FFT). Processing results of simulation experiments and the GaoFen-3 squint SAR data validate the effectiveness of this method.
- Published
- 2021
26. High-Speed Maneuvering Platforms Squint Beam-Steering SAR Imaging Without Subaperture
- Author
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Xiang-Gen Xia, Bowen Bie, Zheng Bao, Guang-Cai Sun, Liang Guo, and Mengdao Xing
- Subjects
Synthetic aperture radar ,Aperture ,business.industry ,Computer science ,Beam steering ,Filter (signal processing) ,Signal ,symbols.namesake ,Optics ,Frequency domain ,symbols ,General Earth and Planetary Sciences ,Time domain ,Electrical and Electronic Engineering ,business ,Doppler effect - Abstract
This paper investigates the imaging problems in squint beam-steering synthetic aperture radar (SBS-SAR) mounted on high-speed platforms with constant acceleration. The cross-range-dependent range cell migration (RCM) is compensated by keystone transform (KT) and time domain RCM correction (RCMC). By derotation and phase compensation, the KT of Doppler folded signal is achieved without zero-padding. For azimuth processing, the signal is reconstructed by the nonlinear phase and range-dependent derotation. Then, the space-variant (SV) Doppler chirp rate is corrected by time domain azimuth nonlinear chirp scaling (ANCS). After frequency domain matched filtering, the full aperture signal is focused in the 2-D time domain. The algorithm is validated by simulated SAR data, including the evaluation of RCMC with KT, geometric correction, and the focusing performance.
- Published
- 2019
27. Focusing Improvement of Curved Trajectory Spaceborne SAR Based on Optimal LRWC Preprocessing and 2-D Singular Value Decomposition
- Author
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Buge Liang, Jianlai Chen, Yuexin Gao, Guang-Cai Sun, and Mengdao Xing
- Subjects
Synthetic aperture radar ,Computer science ,0211 other engineering and technologies ,02 engineering and technology ,Frequency domain ,Singular value decomposition ,Trajectory ,Range (statistics) ,General Earth and Planetary Sciences ,Preprocessor ,Electrical and Electronic Engineering ,Nuclear Experiment ,Algorithm ,021101 geological & geomatics engineering - Abstract
The curved trajectory can lead to severely 2-D spatial-variance in spaceborne synthetic aperture radar (SAR). The azimuth-variance makes the traditional frequency domain imaging algorithms for the straight trajectory based on the assumption of azimuth translational invariance invalid. To correct the severely 2-D spatial-variance in curved trajectory spaceborne SAR, this paper studies a frequency imaging algorithm based on an optimal linear range walk correction (LRWC) preprocessing and 2-D singular value decomposition (SVD). Before the correction of the 2-D spatial-variance, an optimal LRWC preprocessing is introduced to minimize the azimuth-variance. Subsequently, a range block-SVD is proposed to correct the range-variance and, thus, achieves the accurate range cell migration correction. Finally, the azimuth tandem-SVD method is used to correct the azimuth-variance and, thus, accomplishes the azimuth compression for the whole azimuth scene. Processing of the simulated data validates the effectiveness of the proposed algorithm.
- Published
- 2019
28. A Frequency Domain Backprojection Algorithm Based on Local Cartesian Coordinate and Subregion Range Migration Correction for High-Squint SAR Mounted on Maneuvering Platforms
- Author
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Bowen Bie, Jing Guobin, Tianhua Wei, Guang-Cai Sun, Mengdao Xing, Yi Liang, Xiang-Gen Xia, and Yang Yu
- Subjects
Synthetic aperture radar ,Computer science ,010401 analytical chemistry ,0211 other engineering and technologies ,02 engineering and technology ,Filter (signal processing) ,01 natural sciences ,0104 chemical sciences ,law.invention ,Domain (software engineering) ,Range (mathematics) ,symbols.namesake ,law ,Frequency domain ,Trajectory ,symbols ,General Earth and Planetary Sciences ,Cartesian coordinate system ,Electrical and Electronic Engineering ,Doppler effect ,Algorithm ,021101 geological & geomatics engineering - Abstract
Accurate range modeling, cross-range-dependent range migration, and space-variant Doppler parameter are main issues to be solved in processing high-squint synthetic aperture radar (SAR) data acquired from maneuvering platforms. A frequency domain backprojection algorithm, based on local Cartesian coordinate (LCC) and subregion range cell migration correction, is proposed to deal with these problems. With the proposed algorithm, the range model is built in an LCC system to accurately match the signal characteristics after range walk correction. Then, the compensation of cross-range-dependent range migration is implemented based on properly divided subregions after azimuth spectrum filtering. Finally, the space-variant Doppler parameter and higher order phase terms are coherently integrated in range-Doppler domain to get the focused subregion images with full resolution of the synthetic aperture. The final image of the entire scene is obtained by directly connecting all subregion images. The results of simulated and real SAR data validate the proposed algorithm.
- Published
- 2018
29. Vehicle Trace Detection in Two-Pass SAR Coherent Change Detection Images With Spatial Feature Enhanced Unet and Adaptive Augmentation.
- Author
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Zhang, Jinsong, Xing, Mengdao, Sun, Guang-Cai, and Shi, Xin
- Subjects
SYNTHETIC aperture radar ,CONVOLUTIONAL neural networks ,DATA augmentation ,REMOTE sensing ,CHARGE coupled devices - Abstract
As a typical application of remote sensing technology, change detection can find the ground information changes by acquiring the images of the same region at different times. The change detection using the synthetic aperture radar (SAR) with the advantages of all day and all-weather usually monitors the significant surface change, such as flood disasters and earthquake deformation. However, when it comes to detecting subtle changes such as vehicle traces, the traditional methods ignoring the phase coherence between image pairs cannot intensify these faint changes in the difference image. The SAR coherent change detection (CCD) based on repeat-pass repeat-geometry complex images utilizing both the intensity and phase fraction could exhibit the subtle vehicle trace in the difference image. However, the complicated background and decorrelation factors significantly affect the quality of difference images, further causing great trouble for automatic trace detection. This article proposes the spatial feature enhanced Unet and adaptive data augmentation to realize vehicle trace detection. More specifically, the pseudocolor image is first synthesized based on a two-stage coherence estimation method. Then, considering the long-continuity and parallel distribution of vehicle trace samples, the enhanced Unet is constructed by fusing spatial convolutional neural network and spatial attention mechanism. After that, the adaptation data augmentation strategy is presented by introducing manual registration errors and multiple estimation windows. Finally, the experimental results on the Sandia CCD data and our measured data demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
30. Attributed Scattering Center Extraction Method for Microwave Photonic Signals Using DSM-PMM-Regularized Optimization.
- Author
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Xie, Yiyuan, Xing, Mengdao, Gao, Yuexin, Wu, Zhixin, Sun, Guang-Cai, and Guo, Liang
- Subjects
ORTHOGONAL matching pursuit ,PARTICLE swarm optimization ,MICROWAVES ,SYNTHETIC aperture radar - Abstract
The microwave photonic (MWP) radar has the capability of generating ultrawideband (UWB) signals. It is a challenge to realize accurate extraction of attributed scattering centers (ASCs) from MWP signals. This manuscript presents a scattering parameter estimation method in the image domain for UWB MWP signals. The polar-to-rectangular resampling is required for UWB MWP signals. Therefore, a range-azimuth decoupled representation based on the ASC model is formed. The model parameter estimation is converted into an optimization problem, where the statistics of the target signal and the features of interest are modeled to provide prior information. The distribution spread maximization (DSM) and peak magnitude maximization (PMM) principles in the optimization embody this prior information. The particle swarm optimization (PSO) is utilized to search for the parameters of each ASC in the image domain. Moreover, the orthogonal matching pursuit (OMP) algorithm is introduced to avoid repeated computation. Experimental results conducted on the simulated data, XPATCH data, and real data confirm the effectiveness of the proposed method. The proposed method takes into account the specific features of UWB MWP signals, which are neglected in the existing studies. Therefore, the proposed method performs better in extracting ASC parameters from UWB MWP signals in terms of accuracy and more complete sets. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
31. Time-Domain Autofocus for Ultrahigh Resolution SAR Based on Azimuth Scaling Transformation.
- Author
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Lin, Hao, Chen, Jianlai, Xing, Mengdao, Chen, Xiaoxiang, Li, Ning, Xie, Yiyuan, and Sun, Guang-Cai
- Subjects
AZIMUTH ,SYNTHETIC aperture radar - Abstract
For ultrahigh resolution synthetic aperture radar (SAR), azimuth spectrum aliasing limits the application of frequency-domain autofocus algorithms. Therefore, time-domain autofocus algorithms are often used for ultrahigh resolution SAR imaging. However, the azimuth deramping operation in current time-domain autofocus algorithms may introduce an additional azimuth-dependent phase. This phase can be regarded as a part of the phase error, which significantly reduces the estimation accuracy of the phase error. To address this issue, this article proposes a new time-domain autofocus algorithm based on azimuth scaling transformation (AST) for ultrahigh resolution SAR. In this algorithm, we first adopt the azimuth scaling operation to avoid the azimuth-dependent phase so that the estimation accuracy of error can be greatly improved. Then, for the azimuth-dependent shifts caused by the azimuth scaling operation, we adopt the alignment processing to remove them in azimuth-time domain. Finally, we can estimate the error accurately from the aligned signal. The simulation and measured data were processed to verify the effectiveness of the algorithm. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
32. A Real-Time Imaging Processing Method Based on Modified RMA with Sub-Aperture Images Fusion for Spaceborne Spotlight SAR
- Author
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Jun Yang, Fang Zhou, Jiajia Zhang, and Guang-Cai Sun
- Subjects
Synthetic aperture radar ,Image fusion ,business.industry ,Aperture ,Computer science ,symbols.namesake ,Transmission (telecommunications) ,Aliasing ,Frequency domain ,symbols ,Computer vision ,Time domain ,Artificial intelligence ,business ,Doppler effect - Abstract
The small satellite SAR has received increasing attention due to its flexibility and low cost. But limited by the data transmission technology, real-time transmission of a large amount of raw data generated by the spaceborne spotlight SAR can hardly be achieved. Meanwhile, the azimuth bandwidth of the spotlight mode is larger than the PRF, resulting in aliasing of the azimuth spectrum. Based on these, this paper proposes a real-time scheme for small satellite SAR with spotlight mode. The method can solve the problem of data transmission and eliminate spectrum overlap in Doppler domain by means of sub-aperture processing. The modified range migration algorithm (RMA) is used to perform range compression and range cell migration compensation (RCMC) on sub-aperture data. Then dechirp in the azimuth time domain is applied to obtain the low-resolution complex image focused in the range time-azimuth frequency domain. Finally, all theected onto a grid image with azimuth interval matching the azimuth full-resolution to complete image fusion.
- Published
- 2020
33. An Image-Domain Baseline Error Estimation Method for Azimuth Multi-Channel Sar
- Author
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Jixiang Xiang, Mengdao Xing, Guang-Cai Sun, Liang Guo, Yuqi Wang, and Zijing Zhang
- Subjects
Synthetic aperture radar ,Pixel ,Computer science ,Covariance matrix ,fungi ,0211 other engineering and technologies ,02 engineering and technology ,Iterative reconstruction ,body regions ,Azimuth ,0202 electrical engineering, electronic engineering, information engineering ,020201 artificial intelligence & image processing ,Antenna (radio) ,skin and connective tissue diseases ,Joint (audio engineering) ,Baseline (configuration management) ,Algorithm ,021101 geological & geomatics engineering - Abstract
This paper presents a new method for estimating the baseline error of an azimuth multi-channel SAR antenna in the SAR image domain. In this paper, the expressions of the image domain of multi-channel SAR signals with azimuth baseline errors are derived. The covariance matrix of the image domain signals is obtained by using the joint pixel method. Finally, the least-squares method of image domain is deduced to estimate the azimuth baseline of multi-channel SAR error. Simulation experiments verify the effectiveness of the proposed method.
- Published
- 2020
34. Clutter Suppression and Moving Target Radial Velocity Estimation Method for HRWS Multichannel System based on Subspace Projection
- Author
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Boyu Li, Guang-Cai Sun, and Mengdao Xing
- Subjects
Synthetic aperture radar ,business.industry ,Computer science ,020208 electrical & electronic engineering ,0211 other engineering and technologies ,02 engineering and technology ,Radial velocity ,symbols.namesake ,0202 electrical engineering, electronic engineering, information engineering ,symbols ,Clutter ,Computer vision ,Artificial intelligence ,business ,Projection (set theory) ,Doppler effect ,Subspace topology ,021101 geological & geomatics engineering - Abstract
Ghost targets occur when moving targets are processed as stationary scene in the high-resolution and wide-swath azimuth multichannel SAR system, so moving targets require special treatment. Combining the subspace theory with the system, this paper proposes a clutter suppression method and a moving target radial velocity estimation method. The proposed clutter suppression method does not need pre-processing and it preforms better than the spacetime adaptive processing when the moving target component occupies a large proportion in the received data. And the proposed velocity estimation method has lower time complexity than the method based on the minimum entropy, so it is appropriate for the time sensitive applications. The processing of the airborne measured data verifies the effectiveness of the methods.
- Published
- 2020
35. Unambiguous Signal Reconstruction Algorithm for High Squint Multichannel SAR Mounted on High Speed Maneuvering Platforms
- Author
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Guang-Cai Sun, Mengdao Xing, and Ning Li
- Subjects
Synthetic aperture radar ,Computer science ,Signal reconstruction ,0211 other engineering and technologies ,020206 networking & telecommunications ,02 engineering and technology ,Filter (signal processing) ,Iterative reconstruction ,Signal ,symbols.namesake ,0202 electrical engineering, electronic engineering, information engineering ,Trajectory ,symbols ,Algorithm ,Doppler effect ,021101 geological & geomatics engineering - Abstract
High squint multichannel (HSMC) synthetic aperture radar (SAR) mounted on high speed maneuvering platforms is an available mode to achieve wide swath imaging. However, the traditional multichannel reconstruction methods are not suitable because of range-dependent and time-variant steering vector caused by the nonlinear trajectory. To address the issue, a novel unambiguous signal reconstruction algorithm is proposed in this paper. According to the geometry model, the properties of range-dependent and time-variant steering vector are analyzed. Then, a range-dependent and time-variant inter-channel phase compensation method is proposed to correct the space time spectrum, and the constant steering vector is obtained. Before the reconstruction, the range walk correction (RWC) is performed to remove the mismatch between the reconstruction filters and the squinted signal. Furthermore, a modified spatial domain filter is proposed to reconstruct the unambiguous Doppler spectrum. Finally, simulation results are presented to validate the proposed approach.
- Published
- 2020
36. Long Synthetic Aperture Passive Localization Using Azimuth Chirp-Rate Contour Map
- Author
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Guang-Cai Sun, Mengdao Xing, Jixiang Xiang, Liang Guo, Yuqi Wang, and Zijing Zhang
- Subjects
Synthetic aperture radar ,Frequency-shift keying ,Acoustics ,0211 other engineering and technologies ,Physics::Optics ,020206 networking & telecommunications ,02 engineering and technology ,Signal ,Time–frequency analysis ,Azimuth ,symbols.namesake ,Contour line ,0202 electrical engineering, electronic engineering, information engineering ,symbols ,Chirp ,Physics::Accelerator Physics ,Physics::Atomic Physics ,Nuclear Experiment ,Nonlinear Sciences::Pattern Formation and Solitons ,Doppler effect ,Geology ,021101 geological & geomatics engineering - Abstract
A long synthetic aperture passive localization method for two Frequency shift keying (2FSK) signal via azimuth chirp-rate contour is proposed in this paper. By introducing synthetic aperture radar (SAR) imaging technology into passive localization, Doppler frequency change rate of received signal, which is called as azimuth chirp-rate in this paper, is estimated by azimuth focusing. Then, a grid map is formed on the ground and azimuth chirp-rate of each point is calculated to get an azimuth chirp-rate contour map. In the contour map, signal emitter is located in an azimuth chirp-rate curve in which the azimuth chirp-rate value is equal to its estimate. The azimuth chirp-rate contour map of a ground area varies with position of sensor. Therefore, two different azimuth chirp-rate curves can be obtained through different periods of a trajectory and the intersection of the two curves gives estimate of the emitter location.
- Published
- 2020
37. An Efficient MEO SAR Imaging Algorithm Based on Optimal Imaging Coordinate System
- Author
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Wenkang Liu, Vito Pascazio, Guang-Cai Sun, and Mengdao Xing
- Subjects
Image formation ,Synthetic aperture radar ,020301 aerospace & aeronautics ,Property (programming) ,Computer science ,Coordinate system ,0211 other engineering and technologies ,02 engineering and technology ,symbols.namesake ,0203 mechanical engineering ,Range (statistics) ,symbols ,Doppler effect ,Algorithm ,021101 geological & geomatics engineering - Abstract
The curved trajectory and long synthetic aperture time of medium-earth-orbit (MEO) synthetic aperture radar (SAR) lead to a two-dimensional spatial variation in the signals. Traditional methods treat the range and azimuth variations separately, and usually suffer from high computational complexities. We investigate the Doppler rate distribution across a large scene, and exploit an optimal imaging coordinate system, in which the MEO SAR signals satisfy the azimuth-shift-invariant property. The additional processing of the azimuth spatial variation in MEO SAR imaging algorithms can be avoided, and the efficiency of the image formation processor can be improved. Finally, processing of simulated stripmap-mode data with 2-m resolution can validate the proposed algorithm.
- Published
- 2020
38. Synthetic aperture radar (SAR)
- Author
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Guang-Cai Sun, Liang Guo, and Mengdao Xing
- Subjects
Synthetic aperture radar ,Azimuth ,Basis (linear algebra) ,Computer science ,Process (computing) ,Mode (statistics) ,TOPS ,Rotation (mathematics) ,Signal ,Algorithm - Abstract
This chapter introduced the basic concepts of SAR and the principle of 2D target resolution. Obtaining high range resolution with wideband signal and high azimuth resolution with long synthetic array is the basis of the 2D high-resolution imaging. RDA is widely used in SAR imaging processing. Azimuth-translation invariance is the key of RDA. This chapter described the major processing step of RDA, including range compression, range migration correction and azimuth compression, and derives the signal expression of the key step. With the development of SAR imaging requirements, SAR has developed a variety of working modes. This chapter also introduced the working geometry of Stripmap mode, Spotlight mode, Sliding Spotlight mode, TOPS mode and Scan mode, established the unified signal model for multi-modes and analysed the signal property. In imaging processing for multi modes, a unified focusing algorithm based on FrFT is shown, which can simultaneously process Stripmap, Spotlight, Sliding Spotlight and TOPS SAR mode data. The focusing algorithm is parameterised into a rotation angle or a rotation factor, which is determined by the rotation centre distance. Real data of different modes can be well focused by using different and appropriate rotation angles.
- Published
- 2020
39. Estimation of Surface Soil Moisture during Corn Growth Stage from SAR and Optical Data Using a Combined Scattering Model
- Author
-
Xiaolei Lv, Guang-Cai Sun, Jingchuan Yao, Li Zhang, and Qi Chen
- Subjects
Synthetic aperture radar ,3D optical data storage ,combined scattering model ,Correlation coefficient ,Scattering ,surface soil moisture ,TerraSAR-X ,Landsat ,artificial neural network ,corn ,Inverse transform sampling ,Soil science ,Inversion (meteorology) ,Normalized Difference Vegetation Index ,TheoryofComputation_MATHEMATICALLOGICANDFORMALLANGUAGES ,General Earth and Planetary Sciences ,lcsh:Q ,lcsh:Science ,Water content ,Mathematics - Abstract
As an indispensable ecological parameter, surface soil moisture (SSM) is of great significance for understanding the growth status of vegetation. The cooperative use of synthetic aperture radar (SAR) and optical data has the advantage of considering both vegetation and underlying soil scattering information, which is suitable for SSM monitoring of vegetation areas. The main purpose of this paper is to establish an inversion approach using Terra-SAR and Landsat-7 data to estimate SSM at three different stages of corn growth in the irrigated area. A combined scattering model that can adequately represent the scattering characteristics of the vegetation coverage area is proposed by modifying the water cloud model (WCM) to reduce the effect of vegetation on the total SAR backscattering. The backscattering from the underlying soil is expressed by an empirical model with good performance in X-band. The modified water cloud model (MWCM) as a function of normalized differential vegetation index (NDVI) considers the contribution of vegetation to the backscattering signal. An inversion technique based on artificial neural network (ANN) is used to invert the combined scattering model for SSM estimation. The inversion method is established and verified using datasets of three different growth stages of corn. Using the proposed method, we estimate the SSM with a correlation coefficient R ≥ 0 . 72 and root-mean-square error R M S E ≤ 0.043 cm 3 /cm 3 at the emergence stage, with R ≥ 0 . 87 and R M S E ≤ 0.046 cm 3 /cm 3 at the trefoil stage and with R ≥ 0 . 70 and R M S E ≤ 0.064 cm 3 /cm 3 at the jointing stage. The results suggest that the method proposed in this paper has operational potential in estimating SSM from Terra-SAR and Landsat-7 data at different stages of early corn growth.
- Published
- 2020
40. The Impact of SAR Parameter Errors on the Ionospheric Correction Based on the Range-Doppler Model and the Split-Spectrum Method
- Author
-
Guang-Cai Sun, Fangjia Dou, Xiaolei Lv, Xiao Zhou, Ye Yun, and Qi Chen
- Subjects
Physics ,Synthetic aperture radar ,010504 meteorology & atmospheric sciences ,Mean squared error ,Phased array ,interferometric synthetic aperture radar ,0211 other engineering and technologies ,Phase (waves) ,02 engineering and technology ,Slant range ,01 natural sciences ,split-spectrum method ,parameter errors ,Interferometry ,Interferometric synthetic aperture radar ,General Earth and Planetary Sciences ,lcsh:Q ,ionospheric correction ,range-Doppler imaging model ,lcsh:Science ,021101 geological & geomatics engineering ,0105 earth and related environmental sciences ,Remote sensing ,Group delay and phase delay - Abstract
Interferometric synthetic aperture radar (InSAR) products may be significantly distorted by microwave signals traveling through the ionosphere, especially with long wavelengths. The split-spectrum method (SSM) is used to separate the ionospheric and the nondispersive phase terms with lower and higher spectral sub-band interferogram images. However, the ionospheric path delay phase is very delicate to the synthetic aperture radar (SAR) parameters including orbit vectors, slant range, and target height. In this paper, we get the impact of SAR parameter errors on the ionospheric phase by two steps. The first step is getting the derivates of geolocation with reference to SAR parameters based on the range-Doppler (RD) imaging model and the second step is calculating the derivates of the ionospheric phase delay with respect to geometric positioning. Through the numerical simulation, we demonstrate that the deviation of ionospheric phase has a linear relationship with SAR parameter errors. The experimental results show that the estimation of SAR parameters should be accurate enough since the parameter errors significantly affect the performance of ionospheric correction. The root mean square error (RMSE) between the corrected differential interferometric SAR (DInSAR) phase with SAR parameter errors and the corrected DInSAR phase without parameter errors varies from centimeter to decimeter level with the L-band data acquired by the Advanced Land Observing Satellite (ALOS) Phased Array type L-band SAR (PALSAR) over Antofagasta, Chile. Furthermore, the effectiveness of SSM can be improved when SAR parameters are accurately estimated.
- Published
- 2020
- Full Text
- View/download PDF
41. A Imaging Passive Localization Method for Wideband Signal Based on SAR
- Author
-
Jixiang Xiang, Mengdao Xing, Guang-Cai Sun, Yuqi Wang, Liang Guo, and Jun Yang
- Subjects
Synthetic aperture radar ,business.industry ,Computer science ,0211 other engineering and technologies ,020206 networking & telecommunications ,02 engineering and technology ,Signal ,Domain (software engineering) ,Image (mathematics) ,Azimuth ,0202 electrical engineering, electronic engineering, information engineering ,Range (statistics) ,Computer vision ,Artificial intelligence ,Wideband ,business ,Focus (optics) ,021101 geological & geomatics engineering - Abstract
A imaging passive localization method for wideband signal is proposed in this paper. By introducing synthetic aperture radar (SAR) imaging method, the location of the signal emitter is directly given in SAR image. The key of this method is to focus unknown wideband data in range and azimuth domain. To focus the data in range domain without signal parameter, a new pulse compress method is proposed by constructing reference signal from raw data. To focus the data in azimuth domain without knowing range, a range-searching azimuth focus method is proposed by constructing azimuth focus functions with different range. Simulation result validate the effectiveness of the proposed method.
- Published
- 2019
42. Intersatellite cloud computing system for GF-3 SAR data real-time processing
- Author
-
Jun Yang, Guang-Cai Sun, Yandong Cao, Du Mingang, Mengdao Xing, and Liang Guo
- Subjects
Synthetic aperture radar ,Search engine ,Data processing ,Kernel (image processing) ,Computer science ,business.industry ,Real-time computing ,Cloud computing ,Satellite ,business ,Field-programmable gate array ,Raw data - Abstract
Because of computing and storage limitation of one satellite, it is difficult to process large amounts of data of spaceborne synthetic aperture radars. A new method for networked satellites data processing based on intersatellite cloud computing system (ICCS) using a “stage-by-stage” CS algorithm is proposed in this paper, which is built with FPGA chips as the computing kernel of the system. Different from the traditional CS algorithm processing, the system divides data processing into three stages. The computing tasks are reasonably allocated to different data processing units (i.e. satellites) in each stage. The method effectively saves computing and storage resources of satellites, improves the utilization rate of a single satellite, and shortens the data processing time. GF-3 satellite SAR raw data is processed by the system, with the performance of the method verified.
- Published
- 2019
43. A New Approach for Optimization Selection of Spaceborne SAR Beam Position Parameters
- Author
-
Yandong Cao, Jun Yang, Liang Guo, Du Mingang, Mengdao Xing, and Guang-Cai Sun
- Subjects
Synthetic aperture radar ,Computer science ,010401 analytical chemistry ,0211 other engineering and technologies ,Beam geometry ,02 engineering and technology ,01 natural sciences ,0104 chemical sciences ,Pulse (physics) ,Position (vector) ,Band width ,Physics::Accelerator Physics ,Selection method ,Algorithm ,Selection (genetic algorithm) ,Beam (structure) ,021101 geological & geomatics engineering - Abstract
In this paper, a new optimized selection method of beam position parameters for spaceborne synthetic aperture radar(SAR) is proposed. Aiming at the difficulty in selecting pulse repeatition frequency (PRF) and observation band width in spaceborne SAR beam position design, this paper deduces the iterative relationship between adjacent beam positions in detail from the spaceborne SAR beam geometry, and proposes an automatic optimization and selection method for beam position parameters. The proposed method meets the principles of PRF restriction and maximum observation band width. The PRF and observation band width of one beam position can be optimized and selected at the same time, and the next beam position parameters can be automatically iteratively selected according to the current selection result. Simulation results validate the effectiveness of the proposed method.
- Published
- 2019
44. Focusing of Medium-Earth-Orbit SAR Using an ASE-Velocity Model Based on MOCO Principle
- Author
-
Wenkang Liu, Liang Guo, Yang Lan, Guang-Cai Sun, Jianlai Chen, Mengdao Xing, and Yuexin Gao
- Subjects
Synthetic aperture radar ,Motion compensation ,Singular value ,Quadratic equation ,Computer science ,Trajectory ,Range of a projectile ,General Earth and Planetary Sciences ,Electrical and Electronic Engineering ,Algorithm ,Medium Earth orbit - Abstract
The available focusing algorithms for medium-Earth-orbit (MEO) SAR are all based on the complex nonhyperbolic range equation, which may make it more difficult in imaging processing. In this paper, we model the range equation as the standard hyperbolic form based on the motion compensation (MOCO) principle. However, the conventional two-step MOCO may introduce azimuth spectrum expansion due to the potential large motion error, which can lead to severe azimuth ambiguity. To resolve this problem, we develop an omega-K algorithm based on a modified two-step MOCO and an adaptively straight equivalent (ASE)-velocity model. The algorithm is implemented through three-step processing: 1) the modified two-step MOCO does not compensate for the quadratic motion error (the main factor for the spectrum expansion); 2) an ASE-velocity model is introduced to compensate for the quadratic motion error; and 3) an extended Stolt mapping is proposed to perform the accurate range cell migration correction, and the tandem singular value decomposition-nonlinear chirp scaling algorithm is to correct the azimuth-variant phase error and to perform the azimuth compression. Processing of simulated data and airborne SAR real data validates the effectiveness of the proposed algorithm.
- Published
- 2018
45. A Modified CSA Based on Joint Time-Doppler Resampling for MEO SAR Stripmap Mode
- Author
-
Liang Guo, Xiang-Gen Xia, Wenkang Liu, Guang-Cai Sun, Mengdao Xing, and Jianlai Chen
- Subjects
Synthetic aperture radar ,Image formation ,Computer science ,010401 analytical chemistry ,0211 other engineering and technologies ,Mode (statistics) ,02 engineering and technology ,01 natural sciences ,0104 chemical sciences ,symbols.namesake ,Resampling ,Range (statistics) ,symbols ,General Earth and Planetary Sciences ,Electrical and Electronic Engineering ,Algorithm ,Doppler effect ,021101 geological & geomatics engineering - Abstract
Image formation of large scenes is still challenging in medium-earth-orbit (MEO) synthetic aperture radar (SAR) due to the existence of severe 2-D space variance. In this paper, the properties of space variance are analyzed in detail, and then a variable-coefficient fourth-order range model is adopted to model the space-variant range history of every target in a large scene accurately. A method integrating a modified chirp scaling algorithm with joint time-Doppler resampling is proposed to address the range-variant range cell migration, as well as the azimuth-variant frequency-modulation rate and higher order Doppler parameters. The computational burden and alternative implementation approaches are also discussed. Finally, processing of simulated data for MEO SAR with 2-m resolution is presented to validate the proposed algorithm.
- Published
- 2018
46. An Analytical Resolution Evaluation Approach for Bistatic GEOSAR Based on Local Feature of Ambiguity Function
- Author
-
Yong Wang, Liang Guo, Guang-Cai Sun, Yuexin Gao, Mengdao Xing, and Jianlai Chen
- Subjects
Time delay and integration ,Synthetic aperture radar ,020301 aerospace & aeronautics ,Ambiguity function ,Computer science ,ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION ,0211 other engineering and technologies ,02 engineering and technology ,High Earth orbit ,Bistatic radar ,0203 mechanical engineering ,Feature (computer vision) ,Trajectory ,General Earth and Planetary Sciences ,Electrical and Electronic Engineering ,Algorithm ,021101 geological & geomatics engineering - Abstract
Due to the very high orbit, the apparent features of geosynchronous synthetic aperture radar (GEOSAR) are the curved trajectory and long integration time, which can lead to severe coupling between the azimuth and the range directions and, therefore, complicates the resolution evaluation. The traditional analytical approach based on the 2-D division may produce large resolution error, and the numerical approach may suffer from huge computation burden. Therefore, an analytical resolution evaluation approach for GEOSAR based on the local feature of the ambiguity function is studied in this paper. The proposed approach is validated with simulation data to be of high efficiency and accuracy. In addition, the proposed approach is also demonstrated to be capable of evaluating the resolution for other complex platforms, and of evaluating the 3-D resolution of a SAR system.
- Published
- 2018
47. Moving Target Refocusing Algorithm in 2-D Wavenumber Domain After BP Integral
- Author
-
Dong Qi, Sheng Zhang, Xiang-Gen Xia, Guang-Cai Sun, and Mengdao Xing
- Subjects
Synthetic aperture radar ,Motion compensation ,Frequency band ,Computer science ,Fast Fourier transform ,0211 other engineering and technologies ,020206 networking & telecommunications ,02 engineering and technology ,Geotechnical Engineering and Engineering Geology ,symbols.namesake ,Radar imaging ,0202 electrical engineering, electronic engineering, information engineering ,symbols ,Wavenumber ,Electrical and Electronic Engineering ,Algorithm ,Doppler effect ,021101 geological & geomatics engineering ,Interpolation - Abstract
Focusing moving targets with frequency-domain algorithms may suffer from azimuth spectrum not entirely contained within a pulse-repetition frequency band, which may lead to degraded detection performance due to distributing the energy to the artifacts. In order to avoid this problem, a refocusing algorithm after back-projection integral is proposed. The main idea is first to uniformly and coarsely focus moving targets for detection, and then extract the detected targets for refocusing. By deriving the exact analytic expression of the wavenumber spectrum, motion parameter estimation and motion compensation are directly carried out on the 2-D wavenumber domain of the small-sized extracted data, which involves fast Fourier transform and Inverse Fast Fourier Transform operations only with no interpolation, thus reduces the computational complexity. Then, the final refocused image of the moving target is achieved. Refocusing results of both airborne and spaceborne synthetic aperture radar data are shown to validate the effectiveness of the proposed method.
- Published
- 2018
48. Space‐variant RCMC method for squint beam‐steering SAR imaging on high‐speed manoeuvring platforms
- Author
-
Guang-Cai Sun, Bowen Bie, and Mengdao Xing
- Subjects
Synthetic aperture radar ,conventional Doppler domain RCMC method ,business.industry ,Computer science ,Doppler radar ,Beam steering ,zero‐padding ,Domain (software engineering) ,law.invention ,TK1-9971 ,symbols.namesake ,space‐variant range cell migration components ,law ,Radar imaging ,modified RCMC method ,symbols ,Computer vision ,simulated SAR data ,Artificial intelligence ,Time domain ,Electrical engineering. Electronics. Nuclear engineering ,Electrical and Electronic Engineering ,business ,Doppler effect ,high‐speed platforms - Abstract
The focusing of squint beam-steering synthetic aperture radar (SAR) data is a challenging task for the technical difficulty of space-variant range cell migration correction (RCMC). It is more complicated when considering the manoeuver of high-speed platforms. The conventional Doppler domain RCMC method is with low performance and requires a large amount of zero-padding. This Letter proposes a modified RCMC method which removes the space-variant range cell migration (RCM) components by deramp-keystone transform and then compensates the unified RCM terms in the time domain. Compared with the conventional method, the proposed one is with high performance and can avoid zero-padding. This method is validated by the simulated SAR data.
- Published
- 2019
49. A Novel Two-Step Approach of Error Estimation for Stepped-Frequency MIMO-SAR
- Author
-
Xiang-Gen Xia, Mengdao Xing, Guang-Cai Sun, Jing Guobin, and Zheng Bao
- Subjects
Synthetic aperture radar ,Computer science ,Bandwidth (signal processing) ,MIMO ,0211 other engineering and technologies ,Phase (waves) ,020206 networking & telecommunications ,02 engineering and technology ,Geotechnical Engineering and Engineering Geology ,Range (mathematics) ,0202 electrical engineering, electronic engineering, information engineering ,Electrical and Electronic Engineering ,Constant (mathematics) ,Algorithm ,021101 geological & geomatics engineering ,Communication channel - Abstract
For a multiple-input and multiple-output synthetic aperture radar, stepped frequency chirps can be used to generate high-resolution range profiles (HRRPs) by using spectrum synthesis. However, the presence of channel phase errors may degrade the performance of HRRP synthesis. This letter presents a channel error estimation method to address this problem. First, to obtain a focused subband image, a range phase adjustment by contrast enhancement algorithm is proposed to estimate inner-channel high-order phase errors. Second, a sidelobe balanced model is established to estimate constant phase error from the relationship between the balanced sidelobe and constant phase; the constant phase error can be directly obtained in an efficient manner. Experimental analysis using real data demonstrates the effectiveness of the proposed method.
- Published
- 2017
50. A 2-D Space-Variant Motion Estimation and Compensation Method for Ultrahigh-Resolution Airborne Stepped-Frequency SAR With Long Integration Time
- Author
-
Zhenyu Li, Jianlai Chen, Guang-Cai Sun, and Mengdao Xing
- Subjects
Synthetic aperture radar ,Time delay and integration ,Motion compensation ,Computer science ,business.industry ,010401 analytical chemistry ,0211 other engineering and technologies ,02 engineering and technology ,01 natural sciences ,0104 chemical sciences ,Ultrahigh resolution ,Motion estimation ,General Earth and Planetary Sciences ,Computer vision ,Artificial intelligence ,Electrical and Electronic Engineering ,business ,Image resolution ,021101 geological & geomatics engineering - Abstract
For the ultrahigh-resolution airborne stepped-frequency synthetic aperture radar, very large synthetic bandwidth and very long integration time may lead to a 2-D space-variant (SV) motion error when the aircraft flies off the ideally straight trajectory due to the atmospheric turbulence. This new type of error complicates the motion estimation and motion compensation (MOCO). For the motion estimation, we present a jointly 2-D SV motion error estimation method to simultaneously consider the range-variant motion error and the azimuth-variant motion error. For the MOCO, we propose a 2-D SV-MOCO method. The method is implemented through three processing steps: 1) two-step MOCO for the space-invariant motion error and the range-variant phase error; 2) range block-based chirp-z transform (CZT) for the range-variant envelope error; and 3) range block division for the range-dependent azimuth-variant phase error based on the azimuth subaperture method. Finally, processing of simulated data and real data validates the proposed methods.
- Published
- 2017
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