An accurate imaging focusing method in GEO SAR

The geosynchronous earth orbit synthetic aperture radar (GEO SAR) running in high orbit can capture high resolution radar image in hundreds or thousands of kilometers and offer a very effective way for target reconnaissance and accurate attack in wide swath. The large orbit height brings a lot of advantages, and causes a lot of imaging difficulties for GEO SAR. The conventional lower orbit SAR secondary range compression algorithms are based on the linear trajectory model or the Fresnel approximation. It will cause high order phase error of hundreds radians and result in severe spatial-variance in range direction when it is used in GEO SAR, thus the accurate focusing is difficult to be implemented under the conditions of long synthetic aperture time and large scene. An improved secondary range compression (SRC) algorithm to adapt the GEO SAR imaging requirements at perigee was proposed. Based on the accurate satellite curve trajectory model, the chirp rate of azimuth reference function was analytically derived, and its variance was adaptively compensated and the spatial-variance in range direction was overcome. Under the conditions of 100 seconds in synthetic aperture time and 40 km in distance, the simulation results verify the effectiveness of the algorithm proposed in this paper, and the highly accurate imaging can be implemented in GEO SAR.