Multichannel Back Projection (MC-BP) Algorithm and Its Accelerated Form for HRWS SAR

Spaceborne multichannel (MC) synthetic aperture radar (SAR) can achieve high-resolution and wide-swath (HRWS) imaging. However, for an MC SAR system that does not satisfy the displaced phase center antenna (DPCA) condition, ghosts will appear in the image when the traditional back projection (BP) algorithm based on direct coherent integration is applied. To obtain the image without ghosts, an MC-BP algorithm based on time-domain channel weighting is proposed in this article. Compared with the traditional BP algorithm for single-channel signal, this algorithm just adds a channel-weighting factor in coherent integration. The channel-weighting factor is determined based on the channel index and ambiguity index, which is selected based on the instantaneous space angle of the pixel. Different from the existing MC imaging methods including two steps: signal reconstruction and imaging, the proposed method fulfills the image formation in one step and thus is simpler. Moreover, it can adapt the process of MC and multimode [stripmap, spotlight, sliding spotlight, and terrain observation by progressive scans (TOPSs)] data without any extra operation. To improve the efficiency of the MC-BP algorithm and overcome the defocusing issue caused by the Earth’s curved surface in the spaceborne geometry, a fast MC-BP algorithm based on a local spherical coordinate system, i.e., MC spherical Cartesian fast BP (MC-SCFBP) algorithm, is further developed. The spaceborne SAR simulation results with 0.1-m resolution are given to verify the effectiveness of this algorithm.