2.3.3. SMOS-BEC L4 Surface Soil Moisture

The cloud-free SMOS L4 SSM product—a disaggregated soil moisture at 1 km over the Iberian Peninsula—was used. This product is based on a semi-empirical downscaling approach that combines SMOS and MODIS observations together with data from the European Centre for Medium-Range Weather Forecasts (ECMWF). The product uses a shape-adaptive moving window to integrate the SMOS brightness temperature (L1C v.620) and SSM (L2 v.620) at 25 km, the 16-day Terra MODIS Normalized Difference Vegetation Index (NDVI, MOD13A3 v.5) at 1 km, and the modeled ECMWF Era Retrospective Analysis (ERA)-Interim LST in a linear linking model [51]. The downscaling algorithm is applied separately for daily ascending and descending orbits. As with the previous products, the daily average of ascending and descending data was used.
