Comprehensive Vector Radiative Transfer Model for Estimating Sea Surface Salinity From L-Band Microwave Radiometry

Sea surface salinity (SSS) retrieval from satellitebased microwave radiometer is hampered by uncertainties due to atmospheric and surface scattering contributions. This study presents a comprehensive vector radiative transfer model (VRTM) for estimation of brightness temperature (TB) (for SSS retrieval) from L-band radiometry based on a matrixoperator method. It includes an efficient two-scale model (TSM) that combines a geometrical optics (GO) model and a smallperturbation model (SPM) for computing both the small- and large-scale scattering components of the sea surface. Moreover, it considers the influence of rain effects on TB by including the radiation extinction term (scattering and attenuation). The simulation results using the VRTM were validated with those obtained from the RT4 model for flat sea surface conditions and the RTTOV model for rough sea surface conditions. The relative difference in the estimated TB among the models was small (<1%) for low wind speeds (<1 m/s) and increased up to 3% for high wind speeds and observation angles. Simulations on the influence of wind speed on TB with various parameterizations were further examined. Compared with SMOS-MIRAS and Aquarius measurements, the VRTM simulations agreed well with satellite measurements for both vertically and horizontally polarized TBs with biases of less than 2.2 K for observation angles from 20 degrees to 65 degrees. The binned TBs showed even better results, with a standard deviation of less than 1.45 K and an absolute mean error of less than 1.2 K.

Automated summary

This study proposed a comprehensive vector radiative transfer model for estimating sea surface brightness temperature, which was validated with other models. The results showed that there were differences in the estimated brightness temperature among different models under various wind speed conditions.