The Soil Moisture and Ocean Salinity (SMOS) mission provides a unique new collection of land surface measurements that help to globally estimate soil moisture. These measurements have a limited spatial and temporal coverage and only allow some estimation of the top ~5 cm of the land surface soil moisture. Either the multi-angular brightness temperatures or the retrieved soil moisture estimates can be assimilated into a land surface model to obtain improved continuous estimates of surface soil moisture, but also deeper root-zone. Such soil moisture updates may eventually contribute to improved weather and climate predictions.

The assimilation of SMOS soil moisture retrievals into the Catchment land surface model, as part of the NASA Global Modeling and Assimilation Office GEOS-5 system, is validated against in situ soil moisture observations from different networks. The results show an improved temporal variability in surface as well as root-zone soil moisture estimates. The assimilation of SMOS multi-angular brightness temperatures involves the coupling of the land surface model to a radiative transfer model. Results from both retrieval and radiance assimilation will be compared and discussed in view of the plans for soil moisture assimilation from the future Soil Moisture Active Passive (SMAP) mission.