Simulated HF Doppler spectra obtained with an exact modeling of the EM backscattering by 3D time-evolving sea surfaces

As a long term objective we would like to define the required conditions to detect oil spills, using high frequency surface wave radar (HFSWR). Assuming that the presence of oil spills on the sea surface modifies the surface tension which in turn affects the dynamics of the sea, we would like to determine the minimal surface tension which makes this phenomenon observable on a Doppler spectrum (DS). For this purpose we have developed a simulator based on a linear modeling of the sea and of its temporal variation as well as on an exact modeling of the interactions between the electromagnetic (EM) waves and the environment. We have chosen to implement a full wave model called Elsem3D, developed by ONERA. This tool is based on the method of moments (MoM) which can be accelerated by the fast multipole method (FMM). The issues of such a modeling are numerous, as for example the prohibitive computational time due to the number of temporal realizations required to generate the DS and the dimension of the scene. In this paper, we will discuss these issues and outline how we can overcome them. We will then show results from sinusoidal surfaces and sea surfaces for different sea state configurations.