Research On Signal Processing Of Distributed Spaceborne InSAR And SAR-GMTI

Distributed spaceborne SAR system is a novel spaceborne radar system combining satellite formation flying technology and spaceborne SAR technology perfectly. Through formation flying and cooperation of several satellites, the system utilize Interferometric SAR to measure the large-scale terrain digital elevation model(DEM) with high precision. Ground Moving Target Indication (GMTI) of distributed spaceborne SAR system gives the opportunity for large scale surveillance, spying, and target tracking, position. Because of its special value for military and civil application, the distributed spaceborne SAR system is currently one of the research focuses all around the world.The spaceborne SAR system faces a lot of system theory and technique challenges as well as it improves the performance. Since the system is a multilevel and complex large-scale system concerning broad technology, the novel system design theory and signal processing technique need to be studied to resolve the difficulties in the key techniques. This thesis focuses on the signal processing technique of InSAR and SAR-GMTI of the distributed spaceborne SAR system. The systematic research is carried out in single-baseline and multi-baseline signal processing technique of InSAR and SAR-GMTI in the paper. The research in each chapter is arranged as following:In chapter 2, the single-baseline signal processing techniques of the distributed spaceborne InSAR system are studied. Firstly, an adaptive multiresolution filtering approach for interferometric phase is proposed. In the complicate topographic fields, the long baseline between the two satellites makes the interferometric fringe densely and increases the dispersion of the phase noise. The proposed method can track the phase 2-D changes more accurately and achieve a better attention to removal of the noise and preservation of the topographic details. Secondly, a layover and shadow detection method is proposed for single-baseline InSAR. From the geometrical model and signal model of layover and shadow, the thesis proposed a layover and shadow fields detection technique based on the information theoretic criteria. The layover and shadow fields are separated from the interferometric phase to ensure the validity and reliability of the following processing steps.In chapter 3, the multi-baseline signal processing techniques of the distributed spaceborne InSAR system are studied. Based on the distributed spaceborne multi-baseline InSAR system, we study the detection of layover fields, the estimation of the number of the signal component, the estimation of interferometric phase and phase unwrapping. Firstly, based on the information theoretic criteria method, layover and shadow are isolated from the ordinary interferometric phase fields, and the number of the signal component in the layover fields are estimated. Secondly, interferometric phase estimation and phase unwrapping are studied based on Root-MUSIC and RELAX. In the layover fields, the signal from different fields are separated. Phase unwrapping are carried out in the ordinary interferometric phase fields and the layover fields separately.In chapter 4, the single-baseline signal processing techniques of the distributed spaceborne SAR-GMTI system are studied. Firstly, based on the signal model and statistical model of the two clutter cancellers, the detection performance of SAR-ATI and SAR-DPCA are analyzed and compared, with consideration to the channel amplitude-phase unbalance error, time/frequency synchronization error and the influence of clutter and noise. Secondly, based on the joint probability density function (PDF) of interferogram's phase and amplitude of the two hypotheses"clutter"and"clutter plus signal", the one-step constant false alarm rate(CFAR) detector with interferometric phase or amplitude and the two-step CFAR detector with marginal PDF of interferometric phase or amplitude are analyzed for their capabilities and limitations. A new two-step CFAR detector with conditional PDF and a new two-dimensional CFAR detector are proposed. The likelihood ratio test based on the Neyman-Pearson(NP) criterion is exploited as an upper bound for the performance of the above CFAR detectors. Lastly, the clutter suppression technique are studied based on distributed spaceborne SAR-GMTI system, which includes hybrid along-track and cross-track baseline. When the ground scenes are flat earth, the modified SAR-DPCA and SAR-ATI technique are proposed. When the ground scenes are fluctuant mountainous area, an adaptive SAR-DPCA technique is proposed to settle the problem under some conditions.In chapter 5, we proposed a robust optimum adaptive clutter suppression, moving targets detection, velocity measurement and target relocation technique for distributed spaceborne multi-baseline SAR-GMTI systems. Firstly, Some realistic problems related to the implementation of the processor are investigated, which include system multiplicative phase noise and steering vector mismatch. The diagonally loading techniques is resorted to improve the estimation of clutter statistics in the presence of multiplicative noise. A prior information, like road network information, is integrated into the optimum adaptive processor to reduce moving target steering vector mismatch. Secondly, two hypotheses and multiple hypotheses CFAR testing technique are proposed, which are based on the prior information of road network. Lastly, based on a priori information, the target velocity measurement and relocation technique are proposed, which improve the estimation accuracy with low computation load.In chapter 6, we summarize the major work of the thesis, the innovation point and the problems needs to be improved.