Modeled vs. SMOS L2 Soil Moisture in the Central Part of the Duero Basin (Spain)

The temporal evolution of three soil moisture datasets, which comprised remote sensing, in situ observations and modeled data, was analyzed. The study area is located in the central part of the Duero basin (Spain), where the long-term soil moisture monitoring network REMEDHUS is operating. The soil moisture time series of several representative stations were used as a benchmark during the period January 2010-June 2012. This dataset is compared on a daily basis to the L2 soil moisture product from the Soil Moisture and Ocean Salinity (SMOS) mission in both the ascending and descending orbits. The Soil Water Balance Model-Green Ampt (SWBM-GA) has been calibrated and validated in the REMEDHUS area, and the resulting time series were also compared to the SMOS data. The overall results of the comparisons were acceptable and showed that SMOS L2 agreed better with the modeled data (average correlation coefficient, R, equal to 0.63) than it did with the observed (R = 0.48) data. Through the application of a normalization technique, the systematic differences between SMOS and the in situ or modeled datasets were significantly reduced, with Root Mean Square Difference (RMSD) values in the range of 0.02-0.15 m(3) m(-)3 (average RMSD = 0.07 m(3) m(-3)). The results are closer to and sometimes better than the target accuracy of the SMOS mission (0.04 m(3) m(-3)).