On the effect of atmospheric emission upon the passive microwave polarimetric response of an azimuthally anisotropic sea surface

A numerical investigation is carried out in order to evaluate the impact of the atmospheric emission on passive microwave polarimetric measurements of the ocean wind vector. The apparent full Stokes vector at the top of the atmosphere, due to both the surface and atmospheric brightness temperatures, is simulated. The atmospheric upwelling and downwelling radiation is considered through an unpolarized radiative transfer model, suitable for an atmosphere with non-precipitating clouds and low to moderate rainfall. A wind-generated azimuthally anisotropic sea surface is described by a means a two-scale two-dimensional e.m. model. The surface scattering model takes into account the geometrical tilting of the small-scale capillary waves due to the large-scale gravity waves, including also the effect of foam coverage. A statistical evaluation of the atmospheric contribution impact in the K and Ka band is carried out by using both radiosounding measurements and numerical outputs of a microphysical mesoscale cloud model. Finally, a simplified model function of the passive polarimetric response to ocean wind fields, including the modeled atmospheric effects, is derived.