SENSITIVITY ANALYSIS OF GNSS-R DELAY DOPPLER MAPS TO SOIL MOISTURE AND VEGETATION USING A PHYSICS-BASED MODEL

Global navigation satellite system (GNSS)-reflectometry (GNSS-R) delay-Doppler maps (DDMs) are used in various remote sensing applications over land, including retrieving surface soil moisture. Analyzing GNSS-R DDM sensitivity to such geophysical variables aids in understanding retrieval limitations and performance. This work presents a sensitivity analysis of DDMs to vegetation and soil moisture. The analysis uses the improved geometric optics with topography (IGOT) model, which computes DDMs over topographical lands with bare to intermediate vegetation. This IGOT model was validated using Cyclone GNSS (CYGNSS) DDMs over various validation sites. Analytical sensitivity results of the IGOT model are presented in this paper. Specifically, DDM is sensitive to the amplitude of the Fresnel reflection coefficient of the surface, which incorporates soil moisture. Furthermore, DDM is sensitive to the secant of the incidence angle multiplied by the surface normalized bistatic radar cross section (NBRCS), which includes an exponential term of the vegetation parameter.