Comparison between SMOS and SMAP Sea Surface Salinity and SASSIE In-situ Measurements in the Arctic Ocean

Sea Surface Salinity (SSS) anomalies and near-surface thermohaline stratification are key parameters to improve our understanding of sea-ice retreat and formation in polar regions. Since 2010, the remote sensing salinity missions ESA SMOS (Soil Moisture and Ocean Salinity) and NASA SMAP (Soil Moisture Active Passive) offer unprecedented SSS observations globally (SSS SMOS and SSS SMAP respectively). In this study, we compare these observations with in-situ salinity observations (SSSin-situ) made during the NASA Salinity Field Campaign SASSIE (Salinity and Stratification at Sea-Ice Edge) during the fall of 2022. The SASSIE SSSin-situ were collected by 9 different platforms: CastAway and Underway CTD, Wave Gliders, Thermosalinograph, Snake-salinity, SWIFT drifters, UpTempO buoys, Jet-SSP and ALTO and ALAMO profilers. Because satellite SSS retrievals are impacted by land and sea-ice contaminations, cold temperatures, and surface roughness, mean differences, RMSD and STD between satellite SSS and SSSin-situ are examined as a function of distance from the coast and sea-ice edge, sea surface temperature (SST) and wind speed. We find that SSS SMOS and SSS SMAP are well correlated (0.66 and 0.78 respectively) with similar RMSD when compared with SSSin-situ. Close to the coast (0-150 km), SSS SMAP compare better with SSSin-situ with RMSD (<2 g/kg) lower than that from SSS SMOS. Near the sea-ice edge (0-150 km), SSS SMOS compare better with SSSin-situ with RMSD (<2.5 g/kg) lower than that from SSS SMAP. In cold water (SST<1.5˚C) and low wind speed conditions (< 7 m/s), both SSS SMOS and SSS SMAP are consistent with each other. The RMSD between SSS SMAP and SSSin-situ decreases considerably (<1 g/kg) when SST >1.5˚C, while the RMSD between SSS SMOS and SSSin-situ shows less dependence on SST.