Improving the Accuracy of Sea Level Change Rates Using GNSS Continuously Operating Reference Station

Abstract

Coastal sea level monitoring in Thailand is crucial for various aspects of the country. Tide gauges are commonly used in sea level monitoring; however, since they are affected by land subsidence, this research aims to correct the rate of sea level change by accounting for the impact of land subsidence at the tide gauges using GNSS data from a Global Navigation Satellite System Continuously Operating Reference Station (GNSS CORS). The study analyzed the rate of sea level change in the Gulf of Thailand over a 12-year period, using data from two tide gauges: Ko Lak and Ko Mattaphon. Vertical land displacement rates at the tide gauges were measured using GNSS CORS data over a 5-year period, from the PJRK and CMPN stations. The study found that the sea level change rates at Ko Lak and Ko Mattaphon increased at rates of 2.4-8.4 mm/year. Meanwhile, land subsidence rates from PJRK and CMPN were found to be 4.9-7.7 mm/year. After correcting for land subsidence, the sea level change rates were adjusted to 0.7 mm/year at Ko Lak and -2.1 mm/year at Ko Mattaphon. The results demonstrate that vertical land movement, as measured by GNSS satellite data, significantly influences the sea level change rate.