Soil moisture estimation from ERS/SAR data: toward an operational methodology

Previous studies have shown the possibility of using ERS/SAR data to monitor surface soil moisture from space. The linear relationships between soil moisture and the SAR signal have been derived empirically and thus were a priori specific to the considered watershed. In order to overcome this limit, this study focused on 2 objectives. The first one was to validate over 2 years of data the empirical sensitivity of the radar signal to soil moisture, in the case of 3 agricultural watersheds with different soil compositions and land cover uses. The slope of the observed relationship was very consistent. The second one was to propose an operational methodology for soil monitoring based on ERS/SAR data. The implementation of this methodology is based on 2 steps: the calibration period and the operational period. During the calibration period ground truth campaigns are performed to measure vegetation parameters and the ERS/SAR data is processed only once a field land cover map is established. In contrast during the operational period no vegetation field campaigns are performed and the images are processed as soon as they are available. The results confirm the relevance of this operational methodology since no loss of performance is observed between the calibration and operational periods.