Weixian Tan

DLSLA 3-D SAR imaging algorithm for off-grid targets based on pseudo-polar formatting and atomic norm minimization

This paper concerns the imaging problem for downward looking sparse linear array three-dimensional synthetic aperture radar (DLSLA 3-D SAR) under the circumstance of sparse and non-uniform cross-track dimensional virtual phase centers configuration. Since the 3-D imaging scene behaves typical sparsity in a certain domain, sparse recovery approaches hold the potential to achieve a better reconstruction performance. However, most of the existing compressive sensing (CS) algorithms assume the scatterers located on the pre-discretized grids, which is often violated by the off-grid effect. By contrast, atomic norm minimization (ANM) deals with sparse recovery problem directly on continuous space instead of discrete grids. This paper firstly analyzes the off-grid effect in DLSLA 3-D SAR sparse image reconstruction, and then introduces an imaging method applied to off-gird targets reconstruction which combines 3-D pseudo-polar formatting algorithm (pseudo-PFA) with ANM. With the proposed method, wave propagation and along-track image reconstruction are operated with pseudo-PFA, then the cross-track reconstruction is implemented with semidefinite programming (SDP) based on the ANM model. The proposed method holds the advantage of avoiding the off-grid effect and managing to locate the off-grid targets to accurate locations in different imaging scenes. The performance of the proposed method is verified and evaluated by the 3-D image reconstruction of different scenes, i.e., point targets and distributed scene.创新点下视稀疏线性阵列三维合成孔径雷达(DLSLA 3-D SAR)常常由于跨航向的稀疏阵列安装条件受限等因素出现等效相位中心缺失和非均匀分布的情况,造成跨航向稀疏非均匀采样。对于具有稀疏性的3-D SAR成像场景,压缩感知(CS)方法能够在稀疏非均匀采样情况下获得良好的重构效果。然而,大多数CS算法都是基于离散假设,即假设散射点准确位于离散网格上;当真实散射点与离散网格不重合时,CS算法的重构效果将会受到网格偏离现象(off-grid effect)的影响。与离散的CS算法不同,原子范数最小化方法(ANM)直接在连续域上对稀疏信号进行恢复,不受网格偏离现象的影响。本文首先分析了DLSLA 3-D SAR跨航向稀疏重构时存在的网格偏离现象,然后提出了伪极坐标变换与原子范数最小化结合的成像算法。该算法首先通过距离压缩对波传播方向成像,然后对航迹向和跨航向进行伪极坐标变换,并通过傅里叶变换实现航迹向成像,然后在跨航向利用原子范数最小化方法进行成像。本文提出的方法能够在不同的成像场景中避免网格偏离现象、获得精确的成像结果。不同成像场景(点目标和分布式目标场景)的仿真实验成像结果验证了本文算法的有效性。

Investigation of Azimuth Multichannel Reconstruction for Moving Targets in High Resolution Wide Swath SAR

The azimuth multichannel imaging scheme with the large receive antenna divided into multiple sub-apertures usually leads to azimuth non-uniform sampling, and echoes from all azimuth channels should be reconstructed based on the signal model before conventional SAR imaging. Unfortunately, the multichannel signal model of a moving target is different from that of a fixed target. This paper analyzes the multichannel signal model of the moving target and the effect of the target velocity on azimuth multichannel reconstruction. Based on the multichannel signal mode of the moving target, a new multichannel signal reconstruction algorithm is proposed. Furthermore, the slant range velocity is estimated by computing signal energy distribution. Simulation results on point targets validate the proposed approach.

Near range microwave 3D imaging algorithm based on L1 optimization in range direction for target feature enhancements

Near range microwave three-dimensional (3D) imaging system, which is based on the principle of synthetic aperture radar, can reconstruct the 3D complex image of observing object and obtain object information including shape, structure and scattering characteristics. The system has advantages of high precision, penetrating, non-ionizing radiation. Therefore, it is widely applied in the fields of hidden items detect under human body, biomedical imaging, and so on. The basic principle of the system can be described as follows. In range direction, it transmits and receives broadband electromagnetic signals to achieve high-resolution. At the same time, it achieves two-dimensional azimuth resolution by constructing mechanical synthetic aperture or array real aperture in two orthogonal directions. In near range observing applications, the observing scene is usually complex target, leading to the non-sparsity in azimuth directions of echo data. However, the echo data is sparse in range direction due to the limited penetration of microwave imaging. By analyzing the signal sparsity in range direction of near range microwave 3D imaging, this paper introduces L1 optimization reconstruction method into near range imaging and focuses on the study of target feature enhancement method based on L1 optimized. In detail, the near range 3D imaging geometry and echo model are established in Section 2 and signal sparsity in range direction is also analyzed in this section. Then, L1 optimization method is applied to 3D imaging and the imaging algorithm is deduced in Section 3, and two-step iterative shrinkage (TwIST) method is adopted to achieve the range reconstruction. In Sections 4 and 5, the target feature enhancement performance based on the imaging algorithm of this paper is verified via numerical simulation and near range microwave 3D imaging experiments.

Study on motion compensation of helicopter-borne snapshot imaging radar based on antenna array

The Snapshot imaging radar based on antenna array can achieve high-resolution imaging both in spatial domain and time domain. In this paper, the snapshot imaging radar located on helicopter platform is studied. The paper mainly focused on the influence on the echo caused by the vibration characteristics and non-ideal trajectory of helicopter platform. Firstly, adopting frequency modulated continuous wave signal, the paper analyzes the echo model with motion errors. Then, the error is decomposed into linear and quadratic terms, and the frequency scaling algorithm with motion error compensation is deduced. Finally, the model and methods described in the paper are verified via a snapshot imaging experiment based on antenna array.

Estimation and analysis soil moisture of hunshandake sandy land from polarimetric SAR data

At present, various models are developed for soil moisture retrieval, but the application of polarimetric SAR data to retrieve soil moisture in sandy land is rare. Therefore, it is necessary to develop a method for retrieving soil moisture in sandy land. In this paper, we proposed a model to estimate the soil moisture in Hunshandake Sandy Land. The model does not need to take into account the surface roughness, only using the VV and HH polarization backscattering coefficients can be used to retrieve soil moisture. In addition, diversity of the vegetation over the sandy land is difficult to predict. We selected five samples to analyze the effect of vegetation on the inversion results of soil moisture in sandy land.

Investigation of Wavenumber Domain Imaging Algorithm for Ground-Based Arc Array SAR

Ground-based synthetic aperture radar (GB-SAR) has become an important technique for remote sensing deformation monitoring. However, most of the existing GB-SAR systems realize synthetic aperture by exploiting two closely spaced horn antennas to move along a linear rail. In order to obtain higher data acquisition efficiency and a wider view angle, we introduce arc antenna array technology into the GB-SAR system, which realizes a novel kind of system: ground-based arc array SAR (GB-AA-SAR). In this paper, we analyze arc observation geometry and derive analytic expressions of sampling criteria. Then, we propose a novel wavenumber domain imaging algorithm for GB-AA-SAR, which can achieve high image reconstruction precision through numerical solutions in the wavenumber domain. The proposed algorithm can be applied in wide azimuth view angle scenarios, and the problem of azimuth mismatch caused by distance approximation in arc geometric efficient omega-k imaging can be solved successfully. Finally, we analyze the two-dimensional (2D) spatial resolution of GB-AA-SAR, and verify the effectiveness of the proposed algorithm through numerical simulation experiments.

Three-Dimensional Microwave Imaging for Concealed Weapon Detection Using Range Stacking Technique

Three-dimensional (3D) microwave imaging has been proven to be well suited for concealed weapon detection application. For the 3D image reconstruction under two-dimensional (2D) planar aperture condition, most of current imaging algorithms focus on decomposing the 3D free space Green function by exploiting the stationary phase and, consequently, the accuracy of the final imagery is obtained at a sacrifice of computational complexity due to the need of interpolation. In this paper, from an alternative viewpoint, we propose a novel interpolation-free imaging algorithm based on wavefront reconstruction theory. The algorithm is an extension of the 2D range stacking algorithm (RSA) with the advantages of low computational cost and high precision. The algorithm uses different reference signal spectrums at different range bins and then forms the target functions at desired range bin by a concise coherent summation. Several practical issues such as the propagation loss compensation, wavefront reconstruction, and aliasing mitigating are also considered. The sampling criterion and the achievable resolutions for the proposed algorithm are also derived. Finally, the proposed method is validated through extensive computer simulations and real-field experiments. The results show that accurate 3D image can be generated at a very high speed by utilizing the proposed algorithm.

Atmospheric phase correction based on coherent scatterers in GB-SAR interferometry using a single InSAR Pair

Recently ground-based synthetic aperture radar (GB-SAR) has been an important technical means in remote sensing deformation monitoring. However, similar to spaceborne and airborne SAR, the accuracy of GB-SAR interferometry is also seriously affected by atmospheric phase disturbances. In this paper, a novel GB-SAR atmospheric phase correction (APC) algorithm based on coherent scatterers (CSs) is proposed. Firstly, coherent scatterers is selected by frequency interleaved sub-images entropy [1], which only use a single pair of echo data. Then spatial correlation is used for distinguish the stable control points among the coherent scatterers. Finally, the atmospheric phase screen (APS) can be obtained by spatial interpolation and polynomial fitting of the stable control points, which has zero deformation phase. Compared with the existing atmospheric phase correction algorithms, the proposed algorithm using short temporal characterized properties, which is more suitable for GB-SAR real-time deformation monitoring. And due to the spatial correlation of atmospheric phase, the new algorithm has strong robustness by combination of spatial interpolation and polynomial fitting.

Study on fine feature description of multi-aspect SAR observations

The target feature is sensitive to the aspect angle of SAR observation, making the interpretation and target recognition of the SAR image difficult. The information acquired from a certain aspect angle is partial and incomplete, and the multi-aspect observations have the potential to improve the SAR performance in this aspect. Three topics of fine feature description of multi-aspect SAR observations are discussed, and they are the 3D information extraction, the optimum imaging strategy for anisotropic scatterers, and the multi-aspect scattering feature extraction. The initial results of the real P band airborne circular SAR (CSAR) data and the turn table data show that multi-aspect SAR observations have the encouraging potential capability in target fine feature description.

Development and experiments of multi-aspect ground-based SAR for deformation monitoring

Natural geological disasters such as landslide, mudslide and man-induced mine collapse, landslide and other mountain deformations seriously endanger the personal safety and property of people. GB-SAR (Ground-Based Synthetic Aperture Radar) imaging radar has been developing as an important technical for deformation monitoring. In this paper, a novel multi-aspect ground-based SAR deformation monitoring system is developed and introduced. Firstly, a brief background on ground-based microwave imaging radar for high accurately deformation monitoring is provided. Then, system configuration is given. Finally, some preliminary experiments are presented, and the obtained data is processed to further demonstrate the potential capability and precision of the system.