Earth Observation (EO) data for high resolution soil moisture (SM) monitoring

A wealth of soil-vegetation-atmosphere (SVA) variables, such as soil moisture, leaf area index, land surface temperature, precipitation, ... are globally monitored by satellite observations funded by national and international Space Agencies. They have proven useful for improving understanding of the global water and energy cycles and strengthening applications such as large scale hydrologic modelling, numerical weather prediction (NWP), flood forecasting, and drought monitoring and prediction. Despite the usefulness of existing Earth Observation (EO) products, significant scientific interest remains to enhance the ability to resolve fine-scale surface heterogeneity. In particular, soil moisture patterns at a high spatial resolution (e.g., 100m-1000m) can improve quantitative understanding of the SVA system and boost applications, such as mapping the impact of irrigation on local water budgets, assessing the impact of local soil moisture variability on atmospheric instability, and improving NWP and hydrological modelling at regional scales. Besides, the need for soil moisture information at a high temporal frequency (e.g., sub-daily) as well is becoming increasingly urgent in hydrometeorological research focusing on extreme weather events in a climate change era. Spaceborne Synthetic Aperture Radar (SAR) sensors are currently the most suitable systems to retrieve soil moisture at a high spatial resolution and scales ranging from local to regional and continental. The Copernicus program with its sustained observation strategy for the next decades, through the European Radar Observatory Sentinel-1 (S-1), the S-1 Next Generation satellites, and the forthcoming EU L-band Radar Observation System for Europe (ROSE-L) system, motivates and stimulates the development of operational land surface monitoring at high spatial and temporal resolution. In parallel, scientific and technological studies of new satellite observation concepts, such as the GEOSAR systems, are currently under development in order to resolve the sub-daily changes of surface parameters. In this presentation, examples of soil moisture products at high resolution derived from C- and L-band SAR systems are provided, together with case studies of land applications, such as the detection in time and space of irrigated areas. Besides, a European Space Agency airborne campaign carried out in Southern Italy to investigate the monitoring of rapid changes in soil moisture is presented and results are illustrated. Finally, a European metrology study aiming at combining soil moisture measured by different methods and at different spatial support, from point scale sensors, Cosmic Ray Neutron Sensing and satellite-based remote sensing, is introduced.