Large-Scene Imaging Scheme for Geosynchronous Spaceborne-Airborne Bistatic SAR

Geosynchronous (GEO) spaceborne-airborne bistatic SAR (GEO BiSAR) has wide transmitting beam coverage due to its high altitude of illuminator. In order to broaden the swath of receiver on airborne platform, Terrain Observation with Progressive Scan (TOPS) technique is introduced to the airborne receiver in this paper. Meanwhile, the azimuth multichannel technique is applied to suppress the undersampled ambiguity in Doppler frequency domain caused by the lower PRF of GEO BiSAR transmitter than the receiving beam footprint bandwidth. Firstly, the Doppler characteristics of echo from TOPS receiving are analyzed. Then, deramp the Doppler centroid and apply multi-channel reconstruction method to suppress the undersampled ambiguity. Afterwards, the Two-Step Processing (TSP) is adopted to eliminate the scan ambiguity. Finally, the data is focused in two-dimensional frequency domain based on Omega-K imaging algorithm for GEO BiSAR followed by a modified TSP (MTSP) processing to remove the azimuth aliasing. Simulations are presented to validate the effectiveness of the proposed method.