Large scale operational soil moisture mapping from passive MW radiometry: SMOS product evaluation in Europe & USA
Earth Observation (EO) allows deriving from a range of sensors, often globally, operational estimates of surfacesoil moisture (SSM) at range of spatiotemporal resolutions. Yet, an evaluation of the accuracy of those productsin a variety of environmental conditions has been often limited. In this study, the accuracy of the SMOS SSMglobal operational product across 2 continents (USA, and Europe) and a range of land use/cover types is investigated.SMOS predictions were compared against near concurrent in-situ SSM measurements from theFLUXNET observational network. In total, 7 experimental sites were used to assess the accuracy of SMOS derivedsoil moisture for 2 complete years of observations (2010–2011). The accuracy of the SMOS SSM product isinvestigated in different seasons for the seasonal cycle as well as different continents and land use/cover types.Results showed a generally reasonable agreement between the SMOS product and the in-situ soil moisturemeasurements in the 0–5 cm soil moisture layer. Root Mean Square Error (RMSE) in most cases was close to 0.1m3 m−3 (minimum 0.067m3 m−3). With a few exceptions, Pearson’s correlation coefficient was found up toapprox. 55%. Grassland, shrublands and woody savanna land cover types attained a satisfactory agreementbetween satellite derived and in-situ measurements but needleleaf forests had lower correlation. Better agreementwas found for the grassland sites in both continents. Seasonally, summer and autumn underperformedspring and winter. Our study results provide supportive evidence of the potential value of this operationalproduct for meso-scale studies in a range of practical applications, helping to address key challenges presentnowadays linked to food and water security.