Coupled Model Simulation of Wind Stress Effect on Far Wakes of Ships in SAR Images

A high-resolution 3-D hydrodynamic model capable of simulating far wakes of ships has been implemented using computational fluid dynamics software. We feed the surface velocity field produced by the hydrodynamic model into a numerical radar imaging model to simulate synthetic aperture radar (SAR) signatures of the wake. Potential capabilities of this modeling method are demonstrated for an example of wind stress effects on the centerline (turbulent) ship wake. The numerical simulations show that an interaction of the wind-induced surface current with circulations in the ship wake results in a convergence zone on the upwind side of the centerline wake and a divergence zone on the downwind side. In the simulated radar image, the convergence zone appears to be bright because of enhanced surface roughness and radar backscattering. The divergence zone looks dark due to an attenuation of short gravity capillary waves and a corresponding reduction of the backscattered power. This combined hydrodynamic and radar imaging model predicts an asymmetry of the centerline wake with respect to the wind direction, which is consistent with observed ship wake signatures in high-resolution satellite SAR images. The approach developed in this work could be also useful for simulations of other natural and artificial fine-scale features on the sea surface (sharp frontal interfaces, freshwater plumes, etc.) and their interpretation in high-resolution SAR imagery.