Evaluation of sea surface salinity observed by Aquarius and SMOS

Sea surface salinity data derived from Aquarius and Soil Moisture and Ocean Salinity (SMOS) missions were compared with observations by Argo floats in the global oceans and outputs from a global ocean data assimilation system to evaluate the quality of the salinity measurements and assess the error structure in the data. Under the condition of sea surface temperature (SST) higher than 5°C and wind speed lower than 15 ms^-1, salinity observed by Aquarius agreed well with the Argo data with an rms difference of 0.6 psu. If we applied spatial and temporal averages over 1° × 1° and one month, the rms difference was reduced to 0.3 psu. The residual of the salinity observation depended significantly on the SST and wind speed, as expected from the principle of salinity measurement. Also bias caused by inaccurate corrections for the galactic radiation and radio frequency interference were considered to contribute largely to differences with in-situ observations.