Research On Technique Of High-resolution And Wide-swath Geosynchronous SAR Images

Geosynchronous Synthetic Aperture Radar(GEO SAR) is a kind of radar system running on the geosynchronous orbit with a certain inclination. As its ultra-high orbit altitude, ultra-long integration time and ultra-wide swath, the GEO SAR has a lot of advantages when compared with the low earth orbit SAR(LEO SAR). As the development of SAR technique, LEO SAR couldn’t fulfill the people’s requirement in long observed time, wide swath, short repeat period. And GEO SAR gradually become a hotspot in SAR research area.Being similar to the other spaceborne SAR system, one of the most important problems in GEO SAR system is SAR focusing. In this paper, we do the research on the focusing problem and some derived problems through the methods of theoretical analysis and simulated verification. The mainly researches in this paper are listed as follows:We analyze the system performances of GEO SAR that have close relations with SAR focusing, such as the nadir-point track, the Doppler course, the yaw steering, the integration time, and the azimuth resolution of GEO SAR. With the analysis and the simulation, some conclusions are reached, and a whole acquaintance of GEO SAR is achieved.A comparison of some familiar high-precision slant range models is performed. After fully considering the imaging precision and the availability of carrying out focusing algorithm, we choose the Taylor expansion model as the slant range model of GEO SAR. To deeply comprehend the character of Taylor expansion model and its influence on SAR imaging, we analyze and simulate the influence of the phase error of each order on impulse response. In addition, we analyze the variation of the model’s phase error along with the orbital element under the parameters of GEO SAR system. Then we use the simulation of the point target imaging based on method of series reversion(MSR) to validate our conclusions.Along with the requirements of high-efficiency, wide swath, long integration time in GEO SAR imaging, we propose three focusing algorithms, respectively. They are SS-RD algorithm, RD-ACS algorithm and RD-3ACS algorithm. The detailed deriving process is given, and the serious azimuth-variance and range-variance in GEO SAR imaging are mainly analyzed and compensated. Based on the research above, the validity of the imaging algorithms are validated through the simulation performed by space borne radar advance simulator(SBRAS).Finally, we analyze the system error in GEO SAR. The influence of the frequency source’s stability is considered, and requirement of the system design is given. The influence of the ionosphere’s variation on GEO SAR imaging is analyzed and simulated. The variation of the satellite gesture is modeled, and its influence on SAR imaging is analyzed. The compensated method is proposed, and the validity of the method is validated.