An Accurate Ocean Doppler Velocity Estimation Approach for Azimuth MC-HRWS SAR System

In recent years, multiple synthetic aperture radar (SAR) satellites, such as Radarsat-2 and Gaofen-3 (GF-3) spaceborne SAR systems have adopted multichannel high-resolution and wide-swath (MC-HRWS) imaging technology, which can overcome the resolution and mapping width limitation of single-channel SAR. However, considering the influence of Doppler velocity of moving targets and signal energy outside the processed Doppler bandwidth (PDB) on azimuth signal reconstruction processing, Doppler distortion of moving targets and ambiguities energy will occur in the final single-look complex (SLC) data. These issues will result in significant Doppler centroid error and high azimuth ambiguity-to-signal ratio (AASR), severely restricting the ability to obtain accurate ocean surface Doppler velocities. Therefore, an accurate ocean Doppler velocity estimation method for the MC-HRWS SAR system was proposed based on a reconstruction algorithm in the imaging process and the azimuth ambiguity signal model. According to the Bayesian principle, the problem of estimating Doppler velocity on the ocean surface has been transformed into an optimization problem for maximizing the Doppler parameters of posterior probability. Simulation comparative experiments revealed that our method outperformed the conventional methods in the cases of low-uniform sampling, particularly in the region with high AASR. In addition, the Doppler velocity estimation results of the GF-3 ultrafine strip-map (UFS) mode also indicate that the proposed method has a good suppression effect on the Doppler velocity estimation error and AASR for the MC-HRWS SAR system.