New total electron content retrieval improves SMOS sea surface salinity

The European Space Agency (ESA)-led SMOS (Soil Moisture and Ocean Salinity) mission aims at monitoring both soil moisture (SM) and ocean surface salinity (OS) on a global scale. The SMOS instrument is a microwave interferometric radiometer which provides visibilities, from which brightness temperatures (TB) maps are reconstructed in the spacecraft' antenna reference frame. In this study, we investigate how to improve the retrieval of salinity thanks to a better knowledge of the ionospheric Total Electron Content (TEC). We show how both the SMOS bias correction (the so-called Ocean Target Transformation, OTT) and the half orbit TEC profile can be obtained from SMOS third Stokes parameter A3 using a location on the SMOS field of view (FOV) where the sensitivity of TB to TEC is highest. The resulting TEC global maps compare favorably with those built from the International Global navigation satellite system Service observations. TEC values obtained from A3 are next used to optimize the OTT estimation for every polarization, and proved to provide more stable values. Finally, improvements achieved in the salinity retrieved from SMOS data are reported.