Numerical simulation of the effect of the sea surface current gradient on the SAR radial velocity

Wave-current interactions are typically neglected when retrieving radial velocities from synthetic aperture radar (SAR) data. In this study, the impact of spatially varying currents on wind waves and swell, and on SAR-derived radial velocity, is simulated using the SWAN wave model and two semi-empirical Doppler models. Simulations were conducted for two wind speeds (5 and 10 m s −1) along with two current profiles (convergent and divergent). The results indicate that the magnitude of variation in wave-induced Doppler velocity (Δ⁢�D) increases with the strength of the current gradient. This is primarily attributed to the increase (decrease) in significant wave height (�s) and the decrease (increase) in peak period (�p) under convergent (divergent) currents. Additionally, convergent currents lead to larger variations in Δ⁢�D. The impact of wind speed is relatively minor. When considering only the modulation of �s, Δ⁢�D exceeds 0.1 m s −1 only in cases where the current front is 1 km wide, and this threshold is surpassed only locally. However, when both �s and �p modulations are taken into account, Δ⁢�D exceeds 0.1 m s −1 over approximately 10 km beyond the front. In contrast, the swell-current interaction under the conditions simulated in this study results in a negligible Δ⁢�D.