Chapter 5 – Spatiotemporal Estimates of Surface Soil Moisture from Space Using the Ts/VI Feature Space

Abstract Earth Observation (EO) has played an imperative role in extending our abilities for obtaining information on the spatio-temporal distribution of surface soil moisture (SSM). A wide range of techniques have been proposed for this purpose. Some of those techniques have based on the integration of satellite-derived estimates of Fractional Vegetation Cover (Fr) and Land Surface Temperature (Ts) in the form of a scatterplot domain, often combining land surface process model simulations. These techniques aim at combining the horizontal coverage and spectral resolution of EO imagery with the vertical coverage and fine temporal continuity of the process models. Herein one such technique - named the “triangle” - has been implemented with EO datasets from both the AATSR and ASTER sensors together with SimSphere land surface model. Validation of the derived SMC maps was undertaken in different sites in Europe representing a variety of climatic, topographic and environmental conditions, for which validated in-situ observations from diverse operational ground observational networks were available. Results indicated a good agreement between the in-situ and both “triangle” schemes for the estimation of SMC (ASTER R – 0.561/AATSR R – 0.844), with the AATSR results again outperforming the ASTER, comparable to previous studies implemented using different types of EO data. Comparisons of the derived SMC maps regionally against other satellite-derived products also showed largely an explainable distribution of SMC in relation to surface heterogeneity. Our results provide strong supportive evidence for the potential value of the “triangle” inversion modelling technique to accurately derive estimates of SMC, and are important steps as well towards efforts focusing on operational implementation of this approach.