Influence of sea surface emissivity model parameters at L-band for the estimation of salinity

In order to prepare the Soil Moisture and Ocean Salinity (SMOS) mission, we present sensitivity studies on a two-scale sea surface emissivity model used to compute brightness temperatures (T-B) from the Sea Surface Temperature (SST), the wind vector, the incidence angle and the Sea Surface Salinity (SSS). We analyse the impact of uncertainties of the model on T-B at 1.4 GHz (lambda(0) = 21 cm), namely we determine the influence of the parametrization of the sea surface permittivity and of the cutoff wavelength lambda(d) (the limit which separates the short scales of the wave spectrum from the large scales). Using two existing permittivity parametrizations we find differences on T-B ranging from 0.4 to 1.1 K. For SST warmer than 12degreesC and incidence angles smaller than 35degrees, the difference on T-B is a bias independent of SSS and weakly dependent on SST. For these small incidence angles, the choice of the cutoff wavelength does not lead to significant differences on T-B. For incidence angles larger than 40degrees, the permittivity parametrization and the choice of lambda(d) are more critical, resulting in a variation of T-B of several tenths of a Kelvin.