Research On Vibrating Target Detection And Imaging In Dual-channel SAR

Target micro-motion conveys extremely useful information for understanding synthetic aperture radar (SAR) images. It means a lot for future military application to study the detection and imaging of micro-motion target. Compared with single-channel SAR, dual-channel SAR has become hot in current study due to the stronger ability in clutter suppression. Therefore, by using the classic micro-motion target, vibrating target as the research object, this dissertation detailedly investigates the method of vibrating target detection and imaging in dual-channel SAR. The main work consists of the following aspects:As to the vibration target echo modeling in dual-channel SAR, equivalent phase center principle and geometry related approximate method have been used to avoid the traditional complex Taylor approximation.As to the vibrating target detection in dual-channel SAR, two methods based on displaced phase center antenna (DPCA) and along-track interferometry (ATI) have been pointed out respectively, which can detect vibrating target quickly and accurately in clutter and system noise. In addition, we concluded that the ATI performance in clutter suppression will be interfered by noise, which may lead peaks to appear in the range cell of static clutter.And then, for vibration parameters estimation in dual-channel SAR, according to the analysis of DPCA signal characteristics, we convert the vibration parameters estimation to estimation of a signal with the form of absolute value of a sine function, and the converting condition is also given. Accordingly, an algorithm combining the Fourier transform with least squares is proposed for estimating. Furthermore, the analysis of micro-Doppler feature of ATI signal indicates the problem of vibration parameters estimation can be converted to parameters estimation of a cosine curve in the time-frequency plane. Based on this, a method which combines the short time Fourier transform (STFT) with generalized Radon transform (GRT) for parameters estimation has been presented. The simulation results show that both the two methods can estimate vibration parameters precisely in low signal-to-noise ratio (SNR).Also, as to the vibration target imaging in dual-channel SAR, at first, by using the paired echo principle (PEP), the phenomenon that target vibration can make ghost images appear on regular SAR imaging has been interpreted. The relationship between vibration parameters and the feature of ghost images has been given, and the conclusion that the higher the frequency the farther the distance between ghost images and the bigger the amplitude the more the ghost images has been obtained. And then, an improved range-doppler (RD) algorithm has been proposed in primary signal domain to make vibration target refocuse in SAR images. Moreover, another improved RD algorithm has been presented in DPCA signal domain as a resolution to the problem that when there is static target in the range cell of vibrating target, the imaging method in primary signal domain can't focus on these two kinds of targets at the same time. Finally, this dissertation points out that compared with the imaging method in primary signal domain, the imaging method in DPCA signal domain requires higher accuracy in vibration frequency estimation, which however, with better interference rejection.