First evaluation of SMOS L2 soil moisture products using in situ observation data of MAVEX on the Mongolian Plateau in 2010 and 2011

This study tried to make a first evaluation of SMOS L2 soil moisture data (ver. 4.00) obtained during ascending orbits using in situ hydrological observation data of a 120 km by 120 km study area on the Mongolian Plateau from April to August in 2010 and from May to September in 2011. Unfortunately, as we could hardly obtain any available data of SMOS L2 soil moisture from descending orbits for evaluation because of Radio Frequency Interferences (RFI), the evaluation results of SMOS L2 soil moisture products only from ascending orbits (5:30-7:00 in local time) were actually analyzed. Although SMOS slightly underestimated the soil moisture contents at a depth of 3 cm, good matching was observed in the response patterns of SMOS and in situ soil moisture data and the differences between these factors were not large. Accordingly, small values of RMSE and bias were obtained between SMOS soil moisture and in situ measured soil moisture at a depth of 3 cm. SMOS was able to estimate surface soil moisture contents with an accuracy of about 0.045 (m(3) m(-3)) in steppe areas of the Mongolian Plateau.