Precision two-dimensional focusing of spaceborne synthetic aperture radar data with range-varying Doppler centroid

An efficient two-dimensional synthetic aperture radar (SAR) processing algorithm based on the exact transfer function is presented. The approximations made are similar to those in the chirp-scaling algorithm but it works with range-compressed data and can easily handle systems with range-varying Doppler centroids. The range-dependent migration is treated as a small perturbation from that of a given range position. This small deviation is corrected by resampling whilst the main migration factor (large in cases of large Doppler centroids) is corrected by a two-dimensional phase multiply. The azimuth compression filter is range-dependent and implemented as in the range-Doppler algorithm. This algorithm can be easily incorporated into SAR processors using the classical range-Doppler algorithm. The authors tested the algorithm on the Seasat Goldstone scene, ERS-1 and RADARSAT data. The interferometric offset tests show that the algorithm is phase-preserving