A Novel 3-D Focusing Scheme for Distributed SAR Tomography

Distributed synthetic aperture radar (SAR) tomography has recently aroused extensive attention due to its 3-D imaging capability and flexibility. However, atmospheric turbulence brings in motion errors, and collaborative work of multiple platforms increases the degree of freedom (DoF) for motion errors and introduces time-frequency synchronization errors. These undesired errors result in severe 2-D image defocusing, making SAR tomography 3-D imaging unattainable. To address these issues, a novel 3-D focusing scheme that can simultaneously compensate for high DoF motion errors and time-frequency synchronization errors is proposed. Firstly, the RCM offset induced by time synchronization errors is corrected through preprocessing. Then, image-quality-based 2-D autofocus is utilized to achieve 2-D focusing. Finally, the effects of linear phase and constant phase introduced by 2-D autofocus are eliminated by image registration and elevation autofocus based on maximizing image sharpness, respectively. Simulation results demonstrate the effectiveness of the proposed 3-D focusing scheme.