Comparison of Sea Surface Salinity Retrieved from Spaceborne Radiometric Observations and Measured In Situ
[11-Apr-2016] Dinnat, E., Le Vine, D., Meissner, T., Boutin, J., and Martin, N.
Presented at the 14th Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment
During the last few years, two satellite missions shared the scientific objective of mapping the global Sea Surface Salinity (SSS), yet their observations showed significant differences. Both the Soil Moisture and Ocean Salinity (SMOS) and the Aquarius/SAC-D missions use L-band (1.4 GHz) radiometers to measure emission from the sea surface and retrieve SSS. SMOS observations started in 2010 and are still ongoing. Aquarius has been acquiring data from August 2011 to June 2015 when the mission ended due to spacecraft failure. Despite the unfortunate loss of Aquarius, there are 3 years and 9 months of concurrent SSS retrievals between both instruments available to be analyzed. In 2015, a new L-band radiometer started observing the ocean as part of the Soil Moisture Active Passive mission (SMAP). SMAP overlapped with Aquarius during 2 months and is still ongoing. Significant differences in SSS retrieved by both SMOS and Aquarius have been reported in the past, with SMOS SSS being generally lower than Aquarius SSS, except for very cold waters where SMOS SSS is the highest overall. Differences were mostly between -1 psu and +1 psu (psu, practical salinity unit), with a significant regional and latitudinal dependence. In 2015, improved data products have been released for both instruments. Our presentation will report comparisons between SSS retrieved by SMOS and Aquarius, and comparisons between satellite SSS and in situ measurements. We will discuss the impact of the latest changes in the SMOS and Aquarius processing on the retrieved SSS and the differences between both instruments. The impact of differences in the retrieval algorithms (e.g. dielectric constant, ancillary sea surface temperature, surface roughness model, Faraday rotation) on the differences in SSS will be analyzed. If the maturity of the SSS retrieval algorithm for SMAP permits, we will also report first comparisons of SMAP SSS with other satellite SSS and in situ data.