Channel Migration Correction for Low-Altitude Airborne SAR Tomography Based on Keystone Transform

Synthetic aperture radar (SAR) tomography (TomoSAR) has a 3-D resolving ability. Most existing 3-D imaging methods for TomoSAR consider the layovers for different channels are the same. However, in the low-altitude airborne cases, the variation of layovers between channels becomes unneglectable. In this letter, we studied the channel migration (CM) phenomenon of sparse TomoSAR under low-altitude scenarios. We derived the model of the differential range from a particular target to different antennas, which is nearly a linear function along the array dimension. Therefore, we applied Keystone transform (KT) on the array axis to correct this CM, and then the traditional compressed sensing-based 3-D imaging methods for TomoSAR can be applied to get the final 3-D reconstruction results. The approach was tested with simulation data and also the real data of the MV3DSAR system, which is a mini drone-borne TomoSAR system. The results demonstrate that the proposed method can provide a more accurate solution to the low-altitude sparse TomoSAR reconstruction problem.