Novel Electromagnetic Method to Retrieve Ocean Surface Salinity and Temperature Using Polarimetric SAR Data

Abstract Ocean circulation plays a vital role in Earth's energy balance by redistributing heat globally and influencing climate. Driven by differences in seawater temperature and salinity, circulation involves dense, cold, salty water sinking and driving deep ocean currents (thermohaline circulation), while warmer, less saline water stays near the surface. These heat transport processes are sensitive to changes from evaporation, precipitation, and ice melt, which can disrupt circulation, affecting climate and marine ecosystems. This study proposes a new method to estimate seawater salinity and temperature using quad‐polarimetric synthetic aperture radar (quad‐PolSAR) data, which are key factors influencing ocean circulation. The method is based on the relationship between the seawater surface's complex dielectric constant and its physical properties, analyzed at the radar's operating frequency. It employs SAR target decomposition theory and a multi‐component scattering model to isolate the single‐bounce backscattering signal from the sea surface. Two data sets are used to verify the proposed method: a simulated data set at L‐band (1.27 GHz) and real Radarsat‐2 data at C‐band (5.405 GHz) from the Strait of Gibraltar. Results show accurate estimation of seawater electromagnetic properties with strong agreement to ground truth. The study finds that L‐band performs better than C‐band, which is affected by multivalued functions. Environmental and system impacts are accounted for using additive Gaussian noise, and the method's sensitivity to signal‐to‐noise ratio is analyzed. This research offers a valuable tool for monitoring ocean conditions relevant to global climate systems.