An Improved Imaging Method Based on Optimal Topographic Imaging Plane Reconstruction for Nonlinear Trajectory SAR

Radar echo signals may experience the significant 2-D space dependence when it comes to the nonlinear trajectory of the synthetic aperture radar (SAR). The backprojection (BP) imaging algorithm is generally effective for achieving satisfactory focused SAR images under this condition. However, the conventional BP algorithm usually selects a uniform reference imaging plane, regardless of the actual topography of the observation scene. In undulating topographies, it has been proved that the range migration of the actual target and its projection point on the reference imaging plane may not remain consistent, leading to residual uncompensated phase errors and resulting in imaging defocusing during nonlinear trajectories. To address this problem, this article proposes an improved imaging method that involves the optimal topographic imaging plane reconstruction based on the image quality evaluation. The coarse plane and subsequent partitioned subplanes are sequentially constructed to create a topographic imaging plane that closely resembles the digital elevation model (DEM). The BP imaging algorithm is then applied to the reconstructed topographic imaging plane to overcome the defocusing problem. Both simulated and actual experiment datasets validate the effectiveness of the proposed method. Moreover, the proposed method significantly alleviates registration difficulties.