High-Squint SAR Imaging of Maritime Ship Targets

High-squint synthetic aperture radar (HS-SAR) imaging technology greatly enhances the flexibility of SAR. However, the existing HS-SAR imaging algorithms are generally based on the assumption that the illuminated target is static during the synthetic aperture formation. As a consequence, the state-of-the-art algorithms are unable to focus on moving targets well, thus leading to displaced and blurred images of the targets. A maritime ship is a typical kind of moving target with complex noncooperative motion, which has received much attention. Thus, it is a difficult but valuable issue to study HS-SAR imaging of ship targets. In this work, the influence of ship translation and fluctuation is theoretically analyzed. On the basis of these analyses, the new conception of "third range compression (TRC)" caused by ship translation is proposed, and the squint minimization (SM) operation is implemented for the compensation of TRC. Moreover, considering that the target Doppler parameters induced by ship fluctuation are related to its position, a novel method called WASH-CLEAN (watershed and CLEAN) is proposed to automatically focus ship scattering points with different swings. Finally, we propose an integrated modified range-Doppler (RD) imaging algorithm by combining the advantages of HS-SAR and inverse synthetic aperture radar (ISAR). The simulation results show the validity and effectiveness of the presented method.