A Wide-Swath Spaceborne TOPS SAR Image Formation Algorithm Based on Chirp Scaling and Chirp-Z Transform

Based on the terrain observation by progressive scans (TOPS) mode, an efficient\ud full-aperture image formation algorithm for focusing wide-swath spaceborne TOPS data is proposed.\ud First, to overcome the Doppler frequency spectrum aliasing caused by azimuth antenna steering,\ud the range-independent derotation operation is adopted, and the signal properties after derotation\ud are derived in detail. Then, the azimuth deramp operation is performed to resolve image folding\ud in azimuth. The traditional dermap function will introduce a time shift, resulting in appearance\ud of ghost targets and azimuth resolution reduction at the scene edge, especially in the wide-swath\ud coverage case. To avoid this, a novel solution is provided using a modified range-dependent deramp\ud function combined with the chirp-z transform. Moreover, range scaling and azimuth scaling are\ud performed to provide the same azimuth and range sampling interval for all sub-swaths, instead of the\ud interpolation operation for the sub-swath image mosaic. Simulation results are provided to validate\ud the proposed algorithm.