A Numerical Model of Radar Scattering from Steep and Breaking Waves

Ocean gravity waves can be rather steep and even breaking depending on wind speed. Analytical modeling of both the evolution of such strongly nonlinear waves and electromagnetic (EM) scattering from them is currently impossible. At the same time, numerical modeling of these processes poses a significant challenge in terms of the complexity of codes and computational time. In this study, we employ an efficient and fast numerical solver which is based on a uniform approach equally convenient when dealing with both hydrodynamic and EM parts of the problem. As a result, a sequence of large-scale wave profiles is produced that follows through all stages of wave breaking. The small-scale roughness is treated statistically by employing the Pierson-Moskowitz spectrum, and it is added on top of smooth gravity waves. Using the EM code, the scattering problem is solved assuming an impedance boundary condition. The same spline description of the surface profiles of gravity waves is used in both hydrodynamic and EM codes. Backscattering cross sections and corresponding Doppler spectra were the subjects of this study. The numerical calculations demonstrate spike events, with the backscattered signal at horizontal polarization exceeding the backscattering signal at vertical polarization.