Monitoring Sea Level Change in Arctic using GNSS-Reflectometry

Long- and short-term variation of water level is critical in the Arctic as this region significantly affects the global climate and ecosystems. The water level changes are conventionally monitored by a tidal gauge. However, installing and maintaining tide gauges for continuous and seamless water level data in the Arctic is challenging due to the extreme environment. In this study, we investigate GNSS-Reflectometry (GNSS-R) as an alternative water level monitoring method in the Arctic, which measures the water levels based on remote sensing technique. Since GNSS performance at high latitudes is degraded due to satellite geometry and ionospheric effects on GNSS signals, an enhanced GNSS-R algorithm is applied, which accurately determines sea levels through enhanced spectrum analysis based on GNSS - including GPS and Galileo - multiple frequencies and statistical reliability verification. In addition, by including Galileo, the number of visible satellites is also increased that tackles another challenge of lack of available observations at high latitudes. The suggested algorithms are validated by analyzing water level changes in St. Michael, Alaska in June 2018. The water levels derived by GNSS-R based tide gauge are compared to independent data from the two neighboring NOAA's St. Michael and Unalakleet tide gauges (ID: 9468132 and 9468333) about 1.5 km and 74 km of GNSS-R based tide gauge, respectively. As a result, a good agreement is confirmed with a high correlation coefficient of up to 0.87. In addition, from a spectral analysis, meaningful harmonic constituents, M2, Kl, and 01 are founded from the sea level changes measured by GNSS-R based tide gauge. In addition, the temporal resolution of the output was significantly increased by adding the Galileo satellites. By implementing the advanced algorithms of GNSS-R, the proposed study successfully measured the highly accurate and precise water level variation in an environmentally challenging region. The experimental results show many promising applications for the Arctic GNSS-R based tide gauge.