RADARSAT based surface soil moisture retrieval on agricultural catchments of Navarre (Spain)

The present paper reports the first results of an ongoing research whose main objective is the development of a simple methodology for initialising and updating the soil moisture component of distributed hydrological models using SAR data. Five RADARSAT-1 images acquired between 27 February 2003 and 2 April 2003 over the Navarre region (Northern Spain) have been processed. Soil moisture, surface roughness and crop parameters have been monitored coinciding with image acquisition dates over La Tejeria experimental watershed (Navarre). Calculated backscattering values have been compared to soil moisture and surface roughness ground measurements fitting empirical linear regression models. In the case of vegetated fields a semi-empirical water cloud model has been applied to account for vegetation effects on the observed backscattering values. Acceptable correlation has been observed between calculated backscattering values and ground measured soil moisture at field and watershed scale, although variability was high between fields belonging to the same vegetation and roughness classes. The physically based Integral Equation Method (IEM) model has been applied seeking for a more consistent approach. IEM reflected observed backscattering trends. However, dispersion was high probably due to an inadequate characterisation of surface roughness variability