Soil moisture index from ERS-SAR and its application to the analysis of spatial patterns in agricultural areas

Soil moisture is an important factor influencing hydrological and meteorological exchange processes at the land surface. Synthetic aperture radar (SAR) backscatter is strongly affected by the volumetric soil moisture content, thus providing the potential to derive spatially distributed soil moisture information. Archives of historic SAR data exist, in which the use is limited by the lack of corresponding ground truth measurements. This study analyzes the potential of using a soil moisture index (SMI) with high spatial resolution to assess the soil moisture status in the absence of ground truth data. The index method is applied to agricultural areas in the catchment of the river Rur in Germany. The SMI was evaluated using antecedent precipitation and the wetting and drying behavior. The spatial patterns of the SMI were analyzed using semivariograms. This study confirms the applicability of a high resolution soil moisture index for monitoring near-surface soil moisture changes, to analyze soil moisture patterns, and indicates the possibility to complement antecedent precipitation as an input to hydrological models.