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

Abstract 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 Soil Moisture Ocean Salinity (SMOS) and NASA Soil Moisture Active Passive (SMAP) offer unprecedented SSS observations globally (SSSSMOS and SSSSMAP, respectively). In this study, we compare these observations with in situ salinity observations (SSSin‐situ) made during the NASA salinity field campaign Salinity and Stratification at Sea Ice Edge (SASSIE) during the fall of 2022. The SASSIE SSSin‐situ were collected by nine different platforms: Castaway and Underway conductivity–temperature–depth (CTD), Wave Gliders, Thermosalinograph, Snake salinity, Surface Wave Instrument Float with Tracking (SWIFT) drifters, Upper Temperature of the Polar Oceans (UpTempO) buoys, Jet Surface Salinity Profiler (Jet-SSP), and Autonomous Lagrangian Thermometric Observer (ALTO) and Air-Launched Autonomous Micro Observer (ALAMO) profilers. Because satellite SSS retrievals are impacted by land and sea ice contaminations, cold temperatures, and surface roughness, mean differences, root-mean-square difference (RMSD), and standard deviation (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 SSSSMOS and SSSSMAP are well correlated (0.66 and 0.78, respectively) with similar RMSD when compared with SSSin‐situ. Close to the coast (0–150 km), SSSSMAP compares better with SSSin‐situ with RMSD (<2 g kg−1) lower than that from SSSSMOS. Near the sea ice edge (0–150 km), SSSSMOS compares better with SSSin‐situ with RMSD (<2.5 g kg−1) lower than that from SSSSMAP. In cold water (SST < 1.5°C) and low wind speed conditions (<7 m s−1), both SSSSMOS and SSSSMAP are consistent with each other. The RMSD between SSSSMAP and SSSin‐situ decreases considerably (<1 g kg−1) when SST > 1.5°C, while the RMSD between SSSSMOS and SSSin‐situ shows less dependence on SST.