Focusing of geosynchronous SAR with nonlinear chirp scaling algorithm

In geosynchronous (GEO) synthetic aperture radar (SAR), the satellite track is curvilinear and the typical assumption of 'stop-and-go' breaks down due to the increase of orbit altitude. Thus, standard imaging algorithms based on the conventional hyperbolic range equation (CHRE) become inadequate. A four-order range equation taking the 'stop-and-go' errors into consideration is adopted to improve the accuracy in the approximation of the range history for GEO SAR. Then, an accurate two-dimensional spectrum is analytically deduced under the curved trajectory model, and a modified nonlinear chirp scaling (NLCS) algorithm is proposed according to this new spectrum. Simulation results validate that the proposed algorithm has better performance than the CHRE-based NLCS algorithm in the GEO cases.