On the Use of GNSS-R for Biomass Studies Over Tropical Forests

A performance assessment of the Cyclone Global Navigation Satellite System (CyGNSS) mission for biomass studies is presented in this paper over Congo and Amazon tropical rainforests. The functional correlation between CyGNSS-derived trailing edge width TE and Avitabile et. al. Above Ground Biomass (AGB) pan-tropical data is evaluated using ICESat-1/GLAS-derived Canopy Height (CH), SMAP-derived Vegetation Optical Depth (VOD), and Polarization Index (PI). The main objective is to investigate the sensitivity of CyGNSS to biomass over dense forest canopies. The potential advantage of CyGNSS as compared to classical monostatic radar missions could rely on the increasing signal attenuation by the upwelling vegetation cover that reduces the coherent scattering component. This term can only be collected in a bistatic radar geometry. Using empirically-derived polynomial fitting functions, preliminary results show that the use of TE allows to estimate AGB up to ~ 400 ton/ha and ~ 250 ton/ha over Congo and Amazon rainforests at low elevation angles ~ [20, 40] º. The analysis using the SMAP-derived microwave vegetation parameters shows that: a) VOD performs well even over rainforests, and b) PI could depend also on the CH levels.