Emissivity of the sea surface roughened by rain: simulation results

The effect of a rain cell within the antenna beam of a down-looking radiometer pointing to the sea surface is three-fold: a) it increases the opacity of the atmosphere and the scattering of the up-welling radiation, b) it creates a surface layer of fresh water, and c) it changes the roughness of the sea surface. The high radiometric accuracy required to determine the sea surface salinity from L-band measurements requires a) the identification of rainy/cloudy conditions, preferably with sensors with a spatial resolution higher than that of the radiometer antenna, and b) an accurate modeling of atmospheric and surface roughness effects, if rainy/cloudy pixels are going to be used in the salinity retrieval process. This paper presents simulation results of the sea surface emissivity oriented to better understand the effect of the rain-induced roughness using a modified Kirchhoff model, which parameters are derived from a sea spectrum that includes wind speed and direction, and rain intensity. Simulation results at L-band and other frequencies of interest are discussed