A Novel Nonplanar Grid Based Fast Back Projection Algorithm for ConGaL-Borne Terrain Matching SAR

By effectively integrating the terrain matching (TM) mode with the Constellation of Geostationary and Low Earth Orbit (ConGaL) Synthetic Aperture Radar (SAR), researchers can achieve quick revisiting, continuous monitoring, and multiple-angle observation of long, narrow, and curved regions of interest (ROI) at a low cost. However, compared to conventional mono-static SAR constellations, the variations in the observation geometry of such advanced remote sensing instruments bring significant challenges for the subsequent signal processing, resulting in most existing SAR imaging algorithms ineffective. In this article, a novel nonplanar grid based fast back-projection algorithm (NNPG-FBPA) is specially designed for the TM mode on ConGaL-SAR (ConGaL-borne TMSAR), which features a nonplanar ROI-oriented grid meshing method that utilizes the World Geodetic System 1984 (WGS84) Earth model, along with a high-efficiency time-domain imaging kernel established upon it. As a result, the mutual coupling between the azimuth and range directions of TMSAR and the vertical and horizontal directions of the imaging grid is significantly alleviated, and the proposed algorithm offers outstanding imaging efficiency, accuracy, and robustness. Experiments for both point target and distributed target are conducted to convincingly demonstrate the performance of the proposed imaging method for ConGaL-borne TMSAR.