EVALUATION OF SURFACE SOIL-MOISTURE DISTRIBUTION BY MEANS OF SAR REMOTE-SENSING TECHNIQUES AND CONCEPTUAL HYDROLOGICAL MODELING

This paper discusses the attempts to derive surface soil moisture info rmation for two catchments under different climates in Europe based on active microwave remote sensing techniques and conceptual hydrologica l modelling. The two catchments were selected as test sites during the MAC-EUROPE'91 campaign. The first catchment, Slapton Wood, is situate d in south-west England. The second catchment, Virginiolo, is situated in Tuscany, Italy. For both sites, multitemporal full polarimetric AI RSAR (C-, L- and P-band) data are available for the summer of 1991. Ba sed on ground-truth data collected during the flights, simple SAR-soil moisture relationships are established, This allows the estimation of the spatial variation of surface soil moisture at the field scale. Fr om hydrological and meteorological data acquired during the experiment , a conceptual water and energy balance model was calibrated. Simulati on results for soil moisture are then compared with SAR-based soil moi sture estimates. The comparison between sampled, modelled and SAR-deri ved soil moisture at the transect scale is acceptable, but the spatial patterns of soil moisture predicted by the conceptual model and the S AR images are different owing to the influence of vegetation. The resu lts are also useful in pointing out some of the major problems encount ered in the application of SAR data at the catchment scale.