Effects of Rough Topography in GNSS-R: A Parametric Study based on a Digital Elevation Model

Understanding the effects of Earth's surface topography in Global Navigation Satellite Systems Reflectometry (GNSS-R) spaceborne data is essential to correct experimental observations so as to achieve accurate Soil Moisture Content (SMC) determination and biomass monitoring. A comprehensive set of observables obtained from Delay Doppler Maps (DDMs) generated on-board Cyclone Global Navigation Satellite Systems (CyGNSS) are evaluated as a function of several topographic parameters derived from a Digital Elevation Model (DEM). Terrain Ruggedness Index (TRI) and profile curvature have a moderate-to-strong impact on CyGNSS-derived trailing edge (TE) and reflectivity Γ for low elevation angles θ _e ~ [20, 30]° (r_tri_Γ ~ -0.39, r_tri_TE ~ 0.39, r_curv_Γ ~ 0.41, r_curv_TE ~ -0.38). On the other hand, local slopes have an influence on Γ and TE for a constant curvature level, while both observables are independent of the slopes for a constant TRI.