New sea surface salinity retrieval methods based on SMOS data

Abstract

The quality of brightness temperatures (TBs) provided by the Soil Moisture and Ocean Salinity (SMOS) satellite is assessed and validated by comparing them with simulated TBs. TB simulations are computed using the default transfer model implemented by the European Space Agency (ESA) level 2 ocean salinity processor, with auxiliary data taken from The European Centre for Medium Range Weather Forecasts (ECMWF). The ascending SMOS data of the western Pacific Ocean region (0 N–30 N, 120 E–150 E) in July and August 2012 are analysed, and biases of several kelvin are observed between the averaged SMOS TB and simulated TB, which strongly affect the accuracy of sea surface salinity (SSS) retrieval. Two methods are proposed in this article to deal with the biases. The first is that the biases are corrected, and the full range of SMOS multiangular TB is used for retrieval. The second is that the biases are not corrected, and only TB at angles of incidence in the range of 35–55 are used. Then all measurements of a given Stokes parameter in a pixel are regressed with respect to angles of incidence using a second-order polynomial fit in order to reduce noise in the TB. Finally, a least squares iterative process is used to retrieve SSS using the fitted TB. The accuracy of the retrieved SSS using the above two methods is estimated by comparing them with the Array for Real-Time Geostrophic Oceanography SSS and the ESA level 2 SSS.