A simple algorithm for sea surface salinity retrieval from L-band radiometric measurements at nadir

Abstract

The small slope approximation (SSA) theory is applied to the prediction of the foam-free sea surface brightness temperatures at L-band and nadir incidence angle. If surface geometry is assumed to be Gaussian, the wind induced polarized brightness temperature signals are integral functions of the product of the directional curvature spectrum harmonics and electromagnetic weighting functions. At nadir incidence angle, these electromagnetic weighting functions are equals in magnitude for horizontal and vertical polarization and exhibit peaky distribution as function of wavenumber. Using these properties together with azimuthal characteristics of the directional curvature spectrum at L-band, the combination of vertically and horizontally polarized brightness temperature signals at normal incidence is shown to form a simple linear equation of the dielectric constant, the SST and the wind direction. A simple analytical inversion algorithm is proposed to retrieve the Sea Surface Salinity without a priori knowledge of the wind speed using the previously established dependence.