Integrating ground-based and remote sensing-based monitoring of near-surface soil moisture in a Mediterranean environment

Spatially explicit near-surface soil moisture ($\theta$) patterns at high temporal resolution play a very important role in environmental modelling for improving risk assessment and for quantifying the effects of climatic seasonality and land use/land cover change on ecosystem services and functions in Mediterranean catchments. Remote sensing data from the European Copernicus mission are highly acknowledged to serve as fast, reliable, and available suppliers for the derivation of area wide, high grid-resolution information (20 m × 20 m) on near-surface soil moisture patterns acquired at a regular temporal resolution (satellite overpass is every six days). To reliably map $\theta$ from remote sensing radar (i.e., Sentinel-1) satellite products, robust calibration with gridded ground-data is needed and use of either sporadically measured or continuously monitored $\theta$ is of crucial importance for validation procedures. This study integrates remote- and ground-based monitoring of local-to field-scale $\theta$ in the Alento hydrological observatory situated in southern Italy. This Critical Zone Observatory was recently established in the Mediterranean Region and equipped with a multi-sensor network infrastructure. The final aim of this study is to develop site-specific calibration functions to relate spectral measurements to gridded topographic features to estimate near-surface soil moisture patterns. Estimation performance will be evaluated by comparing remote sensing-based (Sentinel-1) with ground-based soil moisture measured during satellite overpass. The soil moisture transfer relations will eventually support high temporal catchment-based hydrological modeling of groundwater and surface water fluxes under consideration of the climatic variability and in feedback with the vegetation.