INVESTIGATING THE IMPACT OF COHERENT AND INCOHERENT SCATTERING TERMS IN GNSS-R DELAY DOPPLER MAPS

Forward scattering properties of Earth-reflected Global Navigation Satellite Systems (GNSS) signals are evaluated over land surfaces. The CYclone Global Navigation Satellite System (CYGNSS) End-to-End Simulator (E2ES) is updated. A GNSS-Reflectometry (GNSS-R) model capable of evaluating both the incoherent and the coherent scattering terms is developed based on the Huygens-Kirchhoff principle. The coherent term is studied for incidence angles theta(i) similar to [0,80]degrees over a wide range of surface height standard deviation sigma = [1, 4] cm and Vegetation Optical Depth VOD = [0, 1.5]. This model is validated over a lake with space-borne data as generated using the CYGNSS raw IF processor. Results demonstrate the impact of higher order Fresnel zones on the spatial resolution of GNSS-R over heterogenous areas, showing "ringing" fluctuations in the reflected power near high contrast boundaries. We expect to contribute to the accurate interpretation of datasets over inland water bodies.