Physically Comprehensive Representation of Bragg Facet Doppler Velocity for Wave-Induced Bias Correction in SAR Ocean Surface Currents Retrieval

The direct measurement of radial ocean surface currents (OSC) using SAR remains a major challenge due to wave-induced bias (WB). The bias caused by ocean waves arises from both the inherent motion of the scattering facets and the modulation of these facets by longer-wave orbital motions. Bragg waves are generally regarded as the dominant scatterers of ocean surface electromagnetic signals under moderate wind conditions. Conventional WB correction methods describe the motion of Bragg scatterers primarily through their phase velocity and its angular distribution, which fail to capture the complex influence of realistic sea-states on Bragg scattering intensity and phase. This study proposes a new Wave Bias Correction Model (WBCM) that accounts for the joint modulation of scattering intensity and phase by complex sea-states. Under narrow-band and internally neutral modulation conditions, the model naturally degenerates into the traditional form, with the Bragg contribution reduced to the conventional representation. Using Bragg internal modulation parameters calibrated from airborne along-track interferometric SAR (ATI-SAR) data, WBCM improved WB simulation accuracy by reducing the RMSE by about 81% relative to the KaDOP model in the corresponding validation case, thereby leading to more accurate OSC retrievals. The proposed method provides a new pathway toward improving both the accuracy and physical comprehensiveness of OSC retrieval from SAR.