Relative Permittivity Measurement of Sea and Land by Ground-Based Dual Circularly Polarized GNSS-Reflectometry

The reflection characteristics of electromagnetic (EM) waves can be used to estimate certain environmental properties of the Earth surfaces. In this study, a low-cost and low-complexity dual circularly polarized reception (DCPR) system is used to measure the relative permittivity of land and seawater. This system consists of a custom, phase stable, dual circularly polarized antenna (DCPA) and off-the-shelf receivers for simultaneous reception of direct and reflected global navigation satellite system (GNSS) signals. DCPR offers two distinct improvements in comparison to the dual linear polarization reception. First, the DCPR system enables two low-correlation data streams due to the utilization of GNSS polarization and its orthogonal counterpart. Second, it enables easy observation of the surface scattering characteristics through the behavior of the reflected cross-polarized carrier-to-noise density ratio (C/N-0). The right-hand (RHCP) and left-hand circularly polarized (LHCP) reflection coefficients were extracted from the received C/N-0 streams using the GNSS-interference pattern technique (GNSS-IPT). The extracted signal peaks were fit with low-order curve functions for a better approximation of the Brewster angles. The measured RHCP and LHCP reflection coefficients enabled the determination of the Brewster angle position, leading to the relative permittivity estimate for the reflecting surfaces. The measured mean relative permittivity for the sea was 84.5 and for the land 13.57. The corresponding standard deviations (stds) were 10.48 and 8.05, and the standard error of mean was 0.23 and 0.17, respectively. The main factors for the uncertainties were the topography of sea and land surfaces, randomly distributed vegetation growth on land, and the receiver quantization process.