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 (TB) 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 TB at 1.4 GHz (0 = 21 cm), namely we determine the influence of the parametrization of the sea surface permittivity and of the cutoff wavelength 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 TB ranging from 0.4 to 1.1 K. For SST warmer than 12°C and incidence angles smaller than 35°, the difference on TB 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 TB. For incidence angles larger than 40°, the permittivity parametrization and the choice of d are more critical, resulting in a variation of TB of several tenths of a Kelvin.