The Potential of Spaceborne GNSS Reflectometry for Soil Moisture, Biomass, and Freeze-Thaw Monitoring: Summary of a European Space Agency-Funded Study

This work presents an overview of the activity developed in the frame of a project funded by the European Space Agency (ESA). The research was focused on the study of the potential applications of GNSS Reflectometry (GNSS-R) over land, with an emphasis on soil moisture (SM) and biomass. A study about the sensitivity with respect to the freeze-thaw dynamics was considered as well. The work started with an analysis of the sensitivity of GNSS-R reflectivity collected by the TechDemoSat-1 (TDS-1) experimental satellite, although, to a limited extent, the Cyclone GNSS (CyGNSS) constellation was considered as well. The encouraging sensitivity outcomes led to the development of retrieval algorithms: three different approaches for SM and one for biomass based on neural networks. A more theoretical investigation was carried out to better understand and predict the signal from a satellite platform, which required the updating of two different models. Topography effects and sensitivity to moisture and roughness of a rough soil were included as well as the effect of vegetation cover. The project was carried out by a large team involving different research groups in Europe. It has led to main conclusions and recommendations derived from a beneficial collaboration and fertilization of ideas. The primary approaches and outcomes are summarized here, including comparisons to the recent literature.