A chirp scaling algorithm based on modified range model at apogee in GEO SAR

In geosynchronous synthetic aperture radar (GEO SAR), due to the high orbit curvature, the traditional slant range mode cannot descript the “near-far-near” slant range history at apogee. This paper presented a modified range model in which curvature was negative to descript the range history at apogee in GEO SAR accurately. Based on the modified model, an accurate two-dimension spectrum of GEO SAR echo was obtained. Then, a modified Chirp-Scaling algorithm for apogee in GEO SAR was presented. At the same time, in order to focus wide swath in GEO SAR, the phase error caused by the linear variation of velocity in range direction can be compensated in azimuth processing. Finally, the simulation result of a large scene (100 km×100 km) proves that the CS algorithm based on the modified range model can achieve the focusing image of GEO SAR at apogee.