Soil water content monitoring: a verification of thermal inertia approaches on low spatial, high temporal resolutions images

Soil water content is directly connected with soil evaporation and plant transpiration processes; in particular, soil water content within the root zone, is readily available to evapotranspiration. Thus, in agricultural sciences, the assessment of the spatial distribution of soil water content could be of utmost importance in evaluating crop water requirement. In spite of limitations to applicability due to contingent cloud cover, water content of the upper part of the soil can be determined by applying the thermal inertia approach by coupling optical and thermal infrared images. The thermal inertia formulation, rigorously retrieved on bare soil, has been also verified on soils partially covered by vegetation. In each case, one of the crucial steps is the assessment of the phase difference between surface temperature and solar irradiation. Different approaches allow determining this latter parameter. To this aim, three formulations to retrieve the phase difference were tested: i) the first, assuming a spatially constant value based on the knowledge of the time when maximum surface temperature occurs; ii) other two methods, allowing determining its spatial distribution through three or four thermographies. In this framework, this research is focused to establish the simplest operational approach providing reliable results over time using low-resolution MODIS images collected over an agricultural area of South Italy (Campania). Temporal evolution of the remote sensing estimates have been compared to data collected by the micro-meteorological station installed in a vineyard within the area.