Abstract
Accounting for multipath in Global Navigation Satellite Systems (GNSS) is a difficult task and an important one, especially during the pre-investigation phase for the installation of a permanent GNSS station for positioning or timing applications. Sites with a high level of multipath can cause positioning errors or timing errors resulting in the quality of GNSS products (position or timing) becoming degraded by several metres or nanoseconds. We investigate and attempt to map multipath as part of the site investigation for the installation of the timing antenna for lunar laser ranging applications at the Hartebeesthoek Radio Astronomy Observatory (HartRAO). A high-resolution wavelet power spectrum and a standard deviation parameter are used to map multipath in both the time and frequency domain as well as spatial variations on the sky plot. The high standard deviation values on the sky map are attributed to reflections due to shrubs or trees on the site, while smaller standard deviation areas are attributed to bare soil or less vegetated as this would give constant reflection over time provided the ground has constant moisture. We conclude that the site is suitable for installation of the timing antenna and that a mask of 15°-20° elevation angle will be applied to the timing antenna to minimise multipath at lower elevations.
Highlights
Multipath signals in most Global Navigation Satellite Systems (GNSS) applications are considered noise
We present an experimental study, which aims to map multipath around the new site for the timing antenna for the new Lunar Laser Ranging (LLR) station located at the Hartebeesthoek Radio Astronomy Observatory (HartRAO)
Bilich and Larson (2007) indicated certain limitations associated with MP1 and MP2 derived from Translation Editing and Quality Check (TEQC) software to map multipath environments
Summary
Multipath signals in most Global Navigation Satellite Systems (GNSS) applications are considered noise. Multipath occurs when an electromagnetic signal arrives at an antenna along an indirect path due to the deflection and reflection of the signal by nearby objects or the surface near the antenna (Larson et al, 2008). Multipath signals are caused by surrounding features such as trees or soil reflecting transmitted signals from the satellites to the antenna. Trees affect the frequencies in the L-band, the leaves and the trunk cause shadowing and attenuation, scattering originates from the tree branches, reflection and diffraction are caused mainly by the tree trunk (Schubert et al, 2010). Soil moisture changes affect the phase of the Signal-to-noise ratio (SNR) modulation pattern and its magnitude when a GPS satellite decends or ascends at low elevations (Zavorotny et al, 2010). The Lband signals penetrate further in dry soil as compared to wet soil (Njoku and Entekhabi, 1996)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
