Remote Sensing of Sea Surface Salinity: An Overview with Case Studies

Sea surface salinity (SSS) is critical for studying biological and physical processes in the ocean, such as the global water balance, ocean currents, and evaporation rates. The water and heat fluxes associated with precipitation and evaporation over global oceans are fundamental in regulating climate and weather. Yet measurements of global SSSs are sparse and do not show the required temporal and spatial variability of SSS distributions. Airborne microwave radiometers, such as the Scanning Low-Frequency Microwave Radiometer (SLFMR) and the Salinity, Temperature, and Roughness Remote Scanner (STARRS), have been used successfully to map SSS and its variability, but only in estuaries and coastal waters. Since 2009, SSS has been measured from satellite orbit by the European Soil Moisture and Ocean Salinity satellite, which is designed to provide synthesized SSS maps with a high accuracy. Other salinity-related satellites are being developed, such as Aquarius, which will provide the global view of salinity variability needed for climate studies. The objectives of this paper are to review remote sensing techniques for mapping SSS and to demonstrate the application of microwave radiometry by presenting two case studies.