Can We Retrieve Sea Surface Salinity With Polarimetric Radar Measurements?

Sea surface salinity (SSS) is measured operationally with radiometers [e.g., soil moisture and ocean salinity (SMOS)] with a resolution from 25 to 40 km. In this contribution, we theoretically evaluate radar sensitivity to SSS, especially we focus on synthetic aperture radar (SAR) due to its intrinsic high-resolution imaging capabilities. This work focuses first on the variations in the dielectric properties of seawater with salinity at different SAR frequency bands (P-, L-, and C-bands) and then evaluate the consequences of both on the normalized radar cross section (NRCS) and copolar phase difference (CPD). The main challenge is to disentangle the sensitivity to dielectric properties from the surface roughness contribution in the SAR backscattered signals. In line with the literature, the results show that the NRCS sensitivity with salinity increases with decreasing operating frequency. In addition, we present new theoretical results on salinity sensitivity to CPD that have not been explored in the existing literature.