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

摘要

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