Spaceborne Azimuth Multichannel BiSAR With Geosynchronous Transmitter and LEO Receiver: High-Resolution Wide-Swath Image Formation

Spaceborne azimuth multichannel bistatic synthetic aperture radar (AMC-BiSAR) system employed inclined geosynchronous (GEO) transmitter and low-Earth-orbit (LEO) receiver is capable of providing a vast area of surveillance and fine spatial resolution, which presents great potentials for Earth observation. Nevertheless, owing to complex geometry and big differences of orbital characteristics, high-resolution wide-swath (HRWS) imaging for GEO-LEO AMC-BiSARs remains three major issues: 1) “Stop-and-Go” approximation is invalid because of long round-trip delay and high receiver velocity; 2) Due to the special bistatic configuration, the conventional effective phase center (EPC) operation for unambiguous signal reconstruction cannot be directly used; 3) Two-dimension spatial-variant characteristics of the echo signal caused by nonlinear and nonparallel trajectories of transmitter and receiver raise challenges for BiSAR focusing. To address these problems, starting from modeling geometry of inclined GEO-LEO AMC-BiSAR, an accurate slant range model without “Stop-and-Go” approximation is derived in the paper. Then the new effective positions of the receiving channels in GEO-LEO AMC-BiSARs are obtained based on the geometry, and the unambiguous Doppler spectrum can be recovered effectively. Finally, a nonlinear chirp scaling imaging algorithm based on the time-domain perturbation (TP-NLCS) is derived and presented, which can correct the variation of range cell migration and azimuth frequency modulation rate. Simulation results show the validity of the proposed method, which can implement GEO-LEO AMC-BiSAR HRWS focusing and has fine phase-preserved capability.