Impact of Limited Satellite Visibility on Estimates of Vertical Land Movements

Abstract

The number of Global Navigation Satellite System (GNSS) satellites and their geometry directly affect the quality of positioning and derived satellite products. Accordingly, the International GNSS Service (IGS) recommends GNSS antennas to be installed away from natural and man-made surfaces and structures, which may affect the incoming signals through severe multipath or obstructions. Following these recommendations, continuous GNSS (cGNSS) stations are generally located in low multipath environments with minimal signal obstructions. However, some applications require GNSS antennas to be installed at specific locations in order to measure local processes. In support of sea level studies, cGNSS stations are established at or close to tide gauges in order to accurately monitor the local vertical land movements experienced by the sea level sensors. However, the environment at the tide gauge might not be optimal for GNSS observations due to the aforementioned station-specific effects, which may degrade the quality of coordinate solutions. This study investigates the impact of severe signal obstructions on long-term position time series for some selected stations. A masking profile from an actually obstructed site is extracted, simulated and applied to unobstructed IGS sites. To investigate these effects, we implemented a new feature called azimuth-dependent elevation masking in the Bernese GNSS Software version 5.2. We present our preliminary results on the use of this new feature to study the impact of different obstruction scenarios on long-term GNSS position time series and vertical land movement estimates. The results show that a certain obstruction, with the effect being highly dependent on its severity and azimuthal direction, affects all coordinate components with the effect being more significant for the Up component. Moreover, it causes changes in the rate estimates and increases the rate uncertainty with the effect being site-specific.