Extending the analysis of the matchups from Figure 1, Figure 2 shows satellite minus Argo salinity differences (dSSS) with the same match-ups for SMAP V4.0, V5.0 and SMOS V700. In the open ocean, both SMAP V4.0 and V5.0 show small differences with Argo and no observable differences between the two versions. The exception to this is that V5.0 includes more data near the sea ice with improved sea-ice flagging and masking based on AMSR-2 TB measurements. Large positive biases in the Northern Hemisphere high latitudes are observed in both V4.0 and V5.0. These are partially due to problematic SSS data in the first few months of the SMAP mission, possibly related to instrument calibration.
In comparison, SMOS L2 data has more noise in the open ocean and larger negative biases in the higher latitude polar regions and the Southern Ocean. This is different from SMAP, which has positive biases around Greenland and Norway.