Evaluation of sea surface salinity observed by Aquarius

Sea surface salinity data derived from Aquarius on the SAC-D satellite were compared with observations by Argo floats in the global oceans to evaluate the quality of the Aquarius salinity measurement and assess the error structure in the data. In tropical and mid latitudes, salinity observed by Aquarius agreed well the Argo data with an rms difference of 0.6 psu. In high latitudes where the sea surface temperature is low, a large scatter of data with a deviation up to 2 psu was discernible. The residual of the salinity observation depended significantly on the sea surface temperature, wind speed and relative wind direction, as expected from the principle of salinity measurement.