Analysis of scattering characteristics from inland bodies of water observed by CYGNSS

Abstract

Measurements made by spaceborne Global Navigation Satellite System Reflectometry (GNSS-R) instruments have shown strong reflected power over inland waters that has been attributed to coherent scattering coming from the first Fresnel zone. Previous work in the field has shown the ability of GNSS-R to observe the global surface water distribution by generating dynamic maps of wetlands and other inundated areas. These maps can be generated by leveraging the large difference in received power of the GNSS signals as they reflect from water surfaces compared to land. In this paper, we utilize a full-forward scattering model approach to evaluate the accuracy of these maps. The CYGNSS End-to-End Simulator (E2ES) was extended to include the contributions from coherent surface scattering in heterogeneous regions where the area around the specular point contains both water and land in complex geometries. The simulator is then used to analyze the accuracy of a current approach to estimate the surface water content in the first Fresnel zone from a single measurement, called a fractional water in footprint approach. We find that contributions to the total received power by the scattering from outside the first Fresnel zone as well as CYGNSS instrument effects impact the accuracy of this approach. Furthermore, the measured signal from calibration scattering targets is compared to the results of simulation to validate the scattering model. The work shows that the variability of the peak reflected power over inland bodies of water due to the scene heterogeneities should be accounted for in designing retrieval algorithms to map wetland extent.