Using Envisat Scansar Data for Characterising Scaling Properties of Scatterometer Derived Soil Moisture Information over Southern Africa

Spaceborne scatterometers and radiometers offer soil moisture information with resolutions in the order of a few tens of kilometres. However, hydrologic users often request a resolution in the order of 1 km. Based on the insight that surface soil moisture in part is driven by large scale atmospheric forcing, a temporal analysis was carried out between backscatter on a local (1 km) and a regional (25 km) scale. The resulting scaling layer consist of the coefficient of determination between the two scales, which can be interpreted as the amount of soil moisture variation on the local scale explained by the variation of soil moisture on the regional scale. On locations where a high correlation is achieved, the regional soil moisture information, corresponding to scatterometer derived estimates, can be used directly on the 1 km scale. In agreement with theory, the highest correlations were found over agricultural fields and grasslands.