Reflection measurement of building materials at microwaves

Abstract. Radio waves interact differently with different materials. The knowledge of reflection and transmission characteristics of the electromagnetic waves through and from the building walls is the key in designing a radio propagation model. The dielectric properties of the material determine the behavior of reflection and transmission of the electromagnetic waves. Therefore, an oblique reflection model is implemented in this thesis to estimate the dielectric properties of various walls at frequency range of 0.7–7 GHz (6.3 GHz bandwidth). The measurement setup consists of a four-port vector network analyzer, two wideband dual-polarized cross-shaped Vivaldi antennas and two 8 m long coaxial cables. Measurements for parallel and perpendicular polarizations are achieved simultaneously by using the dual-polarized antennas. Time-domain gating is applied to separate the desired reflection and eliminate all other multiple reflections from the environment and to suppress the Line-of-Sight component from the delayed response. The estimation of dielectric property of a material is an optimization problem where a suitable objective function is minimized to get the appropriate value. A theoretical model is implemented, so that the minimum difference between the theoretical and measured absolute value of reflection coefficient gives an estimated value of complex relative permittivity. The non-linear least squares algorithm is used for optimization purpose. The real and imaginary part of complex relative permittivity is investigated in this thesis. The real part signifies the amount of electric energy stored in a material, and is called dielectric constant whereas the imaginary part is called the loss factor, which signifies the dissipation of the radiated energy. The estimated values are in good agreement with the values found in the literature. The estimated dielectric properties in this study, such as dielectric constant, loss tangent and Brewster angle of the various materials can be utilized further in designing radio propagation models for similar environments

A method for ice thickness characterization using GNSS C/N0 data

Abstract A Dual Circular Polarized (CP) reception method is proposed to simultaneously record direct and reflected signals in GNSS reflectometry. The purpose of using a dual CP antenna system is to exploit incident wave’s polarization variation after reflection. This paper presents the theoretical background for dual CP reception system and the advantage of using dual CP system over a single polarization. Theoretical multipath propagation is validated by measurements performed at frozen Baltic sea. The Right-Hand Circular Polarization (RHCP) and Left-Hand Circular Polarization (LHCP) received signals are post-processed to retrieve information about the measurement environment. The analysis method gives the evidence of penetration of GNSS signal into the layered media and the possibility to characterize ice-thickness or layered media using only C/N0 data

Depolarization due to wedge diffraction in satellite radiowave communication

Abstract In this paper, the depolarization effect due to the electromagnetic wave diffraction from the rooftop wedge of a building at 1.575 GHz frequency is presented. Diffraction measurement was performed using a dual circularly polarized (CP) antenna system. The Right Hand Circularly Polarized (RHCP) Global Positioning System (GPS) satellite transmission was utilized for measurement. The orbital motion of a single satellite enabled diffraction measurement as a function of the receiver depth in the shadow region, while the receiver was static. The experimental result of RHCP signal was compared with a theoretical knife-edge diffraction model, and they were in good agreement. In case of the deep shadow region, we found the levels of left- and right circular polarized signals to be equal, which indicates a strong depolarization of the incident RHCP wave. The observed depolarization for conductive wedge is explained by the geometrical theory of diffraction

Monitoring sea ice thickness using GNSS-Interferometric reflectometry

Abstract This letter presents the analysis of frozen sea surface properties using low-cost and low-complexity terrestrial global navigation satellite system (GNSS) receivers. Monitoring sea ice thickness and the mean sea level (MSL) of the frozen sea are performed using the interference frequency obtained by the GNSS interference pattern (IP) technique. The height variations between the GNSS antenna and the sea surface evaluated using the IP of the direct and reflected carrier-to-noise density ratio (C/N0) are used to find the corresponding MSL. The GNSS-reflectometry (GNSS-R) derived MSL for open sea conditions agreed well with the mareograph data with a root-mean-squared error (RMSE) of 2.72 cm with an R-squared value of 0.9644. For frozen sea, a notable difference was observed between the measured MSL and ground-truth MSL values. This difference was caused by the combined thickness of snow and ice above the frozen sea surface, also known as the total freeboard. Assuming the conditions for hydrostatic equilibrium is satisfied, total freeboard was converted to ice thickness. The ice thickness values agreed well with the published ice charts by the Finnish Meteorological Institute (FMI). The main uncertainty in the extracted ice thickness was due to the thick snow accumulation and unknown snow properties

Dynamic dual polarized GNSS reflectometry using UAV

Abstract In this paper, GNSS-Reflectometry is performed using Unmanned Aerial Vehicle (UAV). Received GNSS multipath signal is utilized to perform environment remote sensing in dynamic and static flight modes. Right-Hand Circular Polarized (RHCP) multipath signal is recorded and its interference frequency is used to estimate the height of UAV above the ground surface. In the dynamic flight mode, the C/N0 level of the reflected Left-Hand Circular Polarized (LHCP) signal is used to indicate the presence of different ground surfaces. In comparison with the ground measurement systems, UAV provides a dynamic and flexible measurement platform, potentially significantly reducing the measurement time. At the same time, measurement signal quality is influenced due to the variation of the UAV altitude. The results presented strongly indicate the possibility of utilizing UAVs as measurement platform for remote sensing using GNSS multipath signal