Study On The Imaging Techniques For Geosynchronous SAR

Geosynchronous orbit synthetic aperture radar (GEO SAR) placed in the geosynchronous orbit satellite is an active detection tool for remote sensing. Compared with the conventional LEO SAR, it has significant potential advantages such as frequent revisit cycles for interesting place, extra wide mapping region, very large observing area, and so on. In view of this, GEO SAR will be in-depth study in this thesis. To begin with, the system characteristics of GEO SAR will be analyzed in detail. Then, based on the GEO SAR system characteristics and drawing on traditional spaceborne SAR research methods and results, theoretical exploration of the of GEO SAR signal modeling and imaging technology will be carried out. This thesis mainly focuses on following aspects of work:In the first place, coordinate systems in space are introduced for GEO SAR system, and the characteristics of GEO SAR system are analyzed. GEO SAR Doppler center frequency and chirp rate expressions are derived and the Doppler properties of GEO SAR are detailed.In the second place, in the aspect of system signal modeling, this thesis focuses on studying GEO SAR distance model. With reference to the history of the real distance, four history range model in GEO SAR imaging processing are given from a different perspective. Then, the phase error of the given range models are analyzed and similarities and differences of them are summarized, as well as their respective characteristics to guide GEO SAR signal modeling, and thus provide a theoretical basis for the imaging process.In the third place, in the aspect of GEO SAR imaging techniques, based on polynomial history range model and advanced squint history range model, GEO SAR frequency domain imaging algorithms are investigated detailedly in this thesis.1、Based on the polynomial history range model, this thesis proposes three kinds of imaging algorithms for GEO SAR. Firstly, the two-dimensional (2-D) spectrum of the polynomial-based is derived by the method of series reversion (MSR). And the Range-Doppler algorithm (RDA) and Chirp-Scaling algorithm (CSA) are designed for GEO SAR directly. Then a modified2-D spectrum based on MSR is obtained and the Omega-K algorithm for GEO SAR processing is presented. Simulation results demonstrate the effectiveness of the polynomial history range model as well as different imaging algorithms.2、In yaw-steering mode, based on the advanced squint history range model, three kinds of imaging techniques for GEO SAR are proposed in this thesis. Due to the characteristics of the advanced range model in the form,2-D spectrum is obtained based on the stationary phase principle (POSP) and the MSR, respectively. And the accuracy of two kinds of given spectrums is compared and analyzed. Then, according to the SAR classic imaging principle of frequency domain, the improved RDA, CSA as well as Omega-K algorithm are presented and studied in detail in yaw steering mode. Simulation results illustrate that the presented imaging algorithms can generate the well focusing performance.