Optical/Thermal-Based Techniques for Subsurface Soil Moisture Estimation

Abstract The aim of this chapter is to evaluate the aptitude of a simple method based on the relationship between remote sensed estimates of sensible heat flux and vegetation index (VI) from a moderate resolution imaging spectroradiometer (MODIS) to retrieve subsurface soil moisture (SM). A high correlation ( R 2  > 0.69) is shown between the remotely sensed temperature vegetation dryness index (TVDI) and soil water content at 10, 40, 60, and 120 cm depths in two agroclimatic zones of the Argentine Pampas. The different factors of the approach (spatial resolution, temporal evolution of TVDI parameters) and soil-vegetation system (root depth, vertical integration) influencing the aptitude of the method are discussed. In soils without physical limitations for root exploration and vegetation type with deep root system, the capability of the method to estimate deep-water status increases. Finally, the study confirms the usefulness of remote sensed optical/thermal technique for understanding hydrological and ecological processes associated with SM in regions with poor data availability.