Radial Velocity Estimation Approach of Ship for Spaceborne Multichannel HRWS SAR SLC Data

Multichannel high-resolution and wide-swath (MC-HRWS) synthetic aperture radar (SAR) systems with digital beamforming (DBF) in azimuth can suppress Doppler ambiguity to realize HRWS SAR imaging. The imaging position deviation of the moving ship in SAR image is caused by the radial velocity, which can be estimated to accurately position the moving ship in SAR image. For MC-HRWS SAR system, radial velocity will cause Doppler spectrum distortion and azimuth ambiguous, which will reduce the accuracy of traditional single-channel SAR radial velocity estimation method. This article presents a high accuracy radial velocity estimation approach for ships based on maximum likelihood (ML) in MC-HRWS SAR system. The influence of the sea background is eliminated by estimating its Doppler centroid, and extracting the azimuth antenna pattern and the system noise power from the signal of background sea clutter. In contrast to the conventional radial velocity estimation methods based on echo data for MC-HRWS SAR, the proposed method enables direct estimation based on focused SAR single-look complex (SLC) data devoid of auxiliary information, the sea clutter interference is small, and the interaction of multiple ships under the same beam irradiation is avoided. The effectiveness of the method is demonstrated via simulation and GaoFen-3 (GF-3) data of ultra-fine strip (UFS)-map mode. Furthermore, the obtained results show that the estimated radial velocity is consistent (6% root-mean-square deviation) with that provided velocity information of AIS data.