Global Navigation Satellite System Reflectometry (GNSS-R) is a microwave remote sensing technique that takes advantage from signals of opportunity emitted by the GNSS constellations (e.g., GPS) to measure the properties of the Earth surface to reflect the signal toward the receiving antenna, thus implementing a sort of bistatic radar configuration for observing the Earth. The application of this technique for measuring ocean wind and waves from space is consolidated, whilst the applications over land are getting interest from the scientific community. This project should demonstrate: i) to what extent what we know from models and past ground/airborne experiments on GNSS-R applications for soil moisture and vegetation biomass is still applicable from space, ii) which additional phenomena one should try to model, iii) which final bio-geophysical products one can deliver and how (with recommendations for future systems). It will exploit previous data sets collected from ground-based and airborne receivers and GNSS-R data delivered by the UK TechnoDemoSAT-1 satellite carrying on board a GNSS-R receiver and the NASA CYGNSS constellation of 8 small satellites. Spaceborne data will be compared to reference data from in-situ sensors and other earth observation products. The physical and electromagnetic phenomena that determine the signal will be investigated through model simulations, to understand specific limitation of spaceborne systems (e.g., related to SNR). The simulator developed in the past will be updated introducing those physical mechanisms peculiar of a spaceborne sensor (e.g., topography). Simulator outputs will help developing methods to retrieve the target parameters (soil moisture and vegetation biomass) from real data. A proper combination of GNSS-R data with virtual (i.e., a priori statistical information) or real (e.g., from other sensors/platforms) measurements will be exploited to overcome the ill-posed retrieval problem.
