Uncertainties on salinity retrieved from SMOS measurements over global ocean

In order to prepare the Soil Moisture and Ocean Salinity (SMOS) mission, we present 1) the sea surface salinity precision that could be achieved with the SMOS radiometer measurements and 2) the time and space scales over which averaged SMOS Tb should remain relatively constant in order to prepare after-launch monitoring of radiometer drifts. Leaving aside errors due to the instrument and the image reconstruction process, the SSS averaged over 200 × 200 km² areas and over 10 days retrieved from SMOS measurements should meet the GODAE requirements with a precision better than 0.1 psu in most oceanic regions, assuming random noise on W and SST of 2 m s^-1 and 1 °C, respectively. On another hand, this requirement will not be met if no a priori information on the wind speed is available. However, it is likely that SMOS Tb will suffer from temporal drifts and/or from regional biases linked to sun disturbances for instance. In these biases are going to be monitored using Tb averages, it will be necessary to take into account wind speed variability.