Soil moisture downscaling activities at the REMEDHUS Cal/Val site and its application to SMOS

The European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) mission will provide accurate global surface soil moisture estimates. However, due to technological limitations, the spatial resolution of SMOS observations is limited to 40-km. This resolution is adequate for many global applications, but restricts the use of the data in regional studies over land, where a resolution of 1–10 km is needed. Different downscaling experiments have been carried out at the REMEDHUS Cal/Val site within the GPS and RAdiometric Joint Observations one-year field experiment (GRAJO) to explore the possibility of enhancing the spatial resolution of SMOS-derived soil moisture estimates. This paper investigates the use of visible/infrared remote sensing data to improve the spatial resolution of passive microwave soil moisture estimates, and presents an approach to down-scale airborne observations acquired with the UPC Airborne RadIomEter at L-band (ARIEL) using LANDSAT imagery. Although a full validation of the method was not possible, preliminary results indicate that with this approach it is feasible to improve the spatial and radiometric resolution of the soil moisture estimates. The comparison with ground-based soil moisture demonstrates the strength of the link between visible/infrared satellite data and soil moisture status, and the potential of adapting this downscaling technique to SMOS-derived soil moisture estimates.