An Evaluation of Low-Cost GNSS-R Technique for The Precise Measurement of Water-Level Fluctuations Utilizing a Height Displacement Tool

Abstract. The problem of sea-level rise, mainly caused by global warming, requires ongoing and comprehensive monitoring through various observation methods. Satellite-based and ground-based surveying techniques are commonly used to monitor sea-level changes. The Global Navigation Satellite System (GNSS) serves as a valuable tool in this context. Besides providing accurate positioning data, GNSS supports both direct and indirect monitoring of environmental conditions through signal propagation in the atmosphere, which aids in modeling ionospheric and tropospheric dynamics. Moreover, analyzing multipath data—often considered as an error source—can reveal valuable insights into the surroundings of GNSS receivers. Recently, GNSS-Reflectometry (GNSS-R) has emerged, utilizing multipath effects to gather data on the Earth’s surface’s physical properties. This study compares the GNSS-R performance of both geodetic-grade and low-cost GNSS receivers by utilizing a ComNav SinoGNSS N2 as geodetic-grade receiver and antenna and a Septentrio Mosaic-x5 low-cost receiver with ArduSimple AS-ANT2B low-cost antenna, both established near above the pond located in ITU Ayazaga Campus. In order to simulate potential variations in water-levels, including tidal fluctuations, the elevations of the antennas were systematically adjusted using a height displacement tool. Subsequently, it was investigated whether the changes in the antenna height were detected by both the geodetic receiver and the low-cost receiver, and the GNSS-R antenna height determination performance of the low-cost receiver/antenna system was revealed. As a conclusion, the discrepancies in antenna height change measurements ranged from 1.4 cm to 3.7 cm for the geodetic receiver, and from 0.7 cm to 5.0 cm for the low-cost setup. Overall, the average height difference for the geodetic-grade receiver was 2.5 cm, while the average height difference for the low-cost receiver was 3.3 cm.