Geo-location error analysis in geosynchronous SAR

The Doppler rate of geosynchronous synthetic aperture radar (GEO SAR) is zero at some orbital positions due to their high altitude. Also, the Doppler frequency varies along the range direction in the squint mode which is widely used in GEO SAR. The above-mentioned Doppler characteristics have serious effects on the calculation of geo-location error, which are not considered in the conventional model. To solve the problem, an accurate model of the geo-location error is derived based on the range-Doppler equations and the geometry of the squint GEO SAR. The proposed model perfectly matches the simulation results, and can be widely used in both the broadside mode and the squint mode of the spaceborne SAR. Furthermore, the sensitivity of the geo-location error to error sources is analysed based on the simulation for GEO SAR. It is found that the satellite velocity error is the main error source of the geo-location error in GEO SAR.