Tan Weixian

Efficient Pseudopolar Format Algorithm for Down-Looking Linear-Array SAR 3-D Imaging

In this letter, a novel 3-D imaging algorithm for down-looking linear-array synthetic aperture radar is presented. The usual algorithms involve either time-consuming interpolations or huge oversampling operations, which adds huge burden to the image formation processor. The proposed algorithm, in contrast, is not only accurate because little approximation has been made but also quite efficient because of two major endeavors that we have made: First, a novel 3-D pseudopolar domain is introduced for the focused data to avoid any oversampling and to make it possible to formulate the image formation process as an interpolation-free image series expansion, and second, convergence acceleration theory in computational mathematics is introduced to accelerate the convergence of the image series expansion. The 3-D imaging capability is evaluated, and the validation of the proposed algorithm is done by exploiting simulated data.In this letter, a novel 3-D imaging algorithm for down-looking linear-array synthetic aperture radar is presented. The usual algorithms involve either time-consuming interpolations or huge oversampling operations, which adds huge burden to the image formation processor. The proposed algorithm, in contrast, is not only accurate because little approximation has been made but also quite efficient because of two major endeavors that we have made: First, a novel 3-D pseudopolar domain is introduced for the focused data to avoid any oversampling and to make it possible to formulate the image formation process as an interpolation-free image series expansion, and second, convergence acceleration theory in computational mathematics is introduced to accelerate the convergence of the image series expansion. The 3-D imaging capability is evaluated, and the validation of the proposed algorithm is done by exploiting simulated data.

Research on the near range imaging of Ground-based SAR system

In this article, a specific problem of Ground-based SAR (GB-SAR) system imaging is introduced. As for GB-SAR, the illuminated area ranges from about 1m to 1000m. As a result, the attenuation of the echo with the range change could not be ignored. At the same time, imaging algorithms processing airborne and space-borne echo data will overlook the attenuation, so normal algorithms have deficiency in processing echo under such condition. Aiming at this specific problem, an echo model considering the attenuation is given at first; and a simulated echo is processed using Range Migration Algorithm. Then, to make up the deficiency of RMA under this specific situation, a method based on confocal imaging theory is given and corresponding simulation result are presented. Finally, the confocal imaging method is validated via experiment of Ground-based SAR system.

Circular SAR experiment for human body imaging

In this paper, the CSAR (circular synthetic aperture radar) technique is introduced firstly. The principle of CSAR 3D (three dimensional) imaging and the spatial wavenumber support are analyzed and the 3D resolution is discussed secondly. Secondly, Ku band fully-polarimetric CSAR human body imaging experiments are performed, and the experimental data is processed by a fast 3D backprojection algorithm, the corresponding amplitude images are shown. Finally, the future experiments for human body imaging are discussed.

SAR Three-Dimensional Imaging Experiments with Microwave Anechoic Chamber SAR Data

In this paper, two 3-D (three-dimensional) imaging techniques, MB-TomoSAR (multi-baseline SAR tomography) and CSAR (circular synthetic aperture radar), are introduced firstly. Secondly, the indoor experimental systems for acquiring SAR data in the microwave anechoic chamber are described, then the experiments of the two 3-D imaging mode for the metallic spheres and human body are performed, respectively. Finally, the 3-D imaging capability of the MB-TomoSAR and CSAR is demonstrated with the experimental data.

Study on SAR image formation for aspect-dependent scatterers

The isotropic scattering point scattering assumption is not hold for wide angle aperture SAR [1]. This paper introduced an image reconstruction method for the scatters objects that have narrow beam patterns and aspect-dependent scattering properties. The directional filter bank is applied to form well-matched subimages, which are noncoherently combined in the Generalized Likelihood Ratio Test (GLRT) image [3]. This noncoherent composite image retains the information of aspect-varying scattering of objects.

A novel imaging approach for multi-baseline SAR tomography

MB-TomoSAR (multi-baseline SAR tomography) is the most promising technique to realize the real 3-D (three-dimensional) resolution of the observed target zones in future. In this paper, the state art of MB-TomoSAR is briefly reviewed firstly. Secondly, a more general MB-TomoSAR model is described, and a novel imaging approach of processing MB-TomoSAR data is proposed base on this general model. Thirdly, the emphasis is placed onto the simulation of MB-TomoSAR, and the method has been proved able to process the MB-TomoSAR data. Finally, a conclusion is given, and the new challenges on MB-TomoSAR in application are discussed.

Burst Mode Imaging with ENVISAT-1 ASAR Alternating Polarisation Data

ENVISAT-1 ASAR (alternating polarisation) AP burst data segments frequency-time energy in Doppler histories according to the position of target relative to the burst timeline, at the same time, the energy that a scatterer contributes to the received echo ensemble depends on the relative scatterer position following the azimuth antenna pattern, hence the focused image exhibits the radiometric modulation, an effect known as scalloping. This paper investigates the applicability of the band-limited RD algorithm to process ENVISAT-1 ASAR AP burst-mode data, and shows its ability to remove the influence of the azimuth antenna pattern and to preserve phase information. Then the paper illustrates a strategy of filtering the power detected image to suppress the periodic modulation of the impulse response. Finally, the band-limited RD algorithm and the method of filtering in image power domain are verified by processing the ENVISAT-1 ASAR AP mode burst data

Multi reference plane projected confocal 3-D imaging algorithm for CSAR

Three dimensional (3D) images can be obtained with SAR moving in a circular trajectory (circular SAR, CSAR) using confocal 3D imaging algorithm (CIA). However, the image formation is very time-consuming due to the 3-D space variant filtering contained in the algorithm. This paper transformed the 3D space variant filtering into a 2D filtering followed by a time shift in the height direction based on the small scale imaging area approximation and presented a projected confocal 3D imaging algorithm (PCIA) for CSAR. To cancel the restriction on PCIA, a multi reference plane projected confocal 3D imaging algorithm (MRPPCIA) was presented. It is found that the disadvantages of CIA such as complexity and inefficiency can be conquered by PCIA and the restriction on PCIA can be cancelled by adoption of MRPPCIA.