Determining complex permittivity from Fresnel coefficients in GNSS- reflectometry

Global Navigation Satellite System Reflectometry (GNSS-R) is a microwave remote sensing technique which has been used in the last twenty years to derive information about the composition or the properties of ground surfaces [1,2]. The received power of the GPS signals reflected by the ground is proportional to the modulus of the perpendicular and parallel polarization Fresnel coefficients (see Fig.1). These coefficients depend on the incidence angle , and on the ground's permittivity which is a complex quantity. The knowledge of  is important for determining the soil moisture conditions and other characteristics of the surface (e.g., salinity, freeze-thaw transitions).