Evaluation of GNSS Reflectometry Method for Sea Level Estimation in Indonesia Lisa A. Cahyaningtyas (a*), Dudy D. Wijaya (a), Bambang Setyadji (a), Ivonne M. Radjawane (b), Hansan Park (c), Rega Himawan (d)
(a) Geodesy and Geomatics Engineering, Institut Teknologi Bandung, Bandung 40132, Indonesia
(b) Oceanography, Institut Teknologi Bandung, Bandung 40132, Indonesia
(c) Marine Technology Cooperation Research Center - Cirebon Center, Cirebon 45611, Indonesia
(d) PT Wisesa Berkah Bumi, Jakarta 133220, Indonesia
Abstract
Over the last decade, GNSS reflectometry (GNSSR) has been developed as a technique for observing sea level height using data from GNSS satellite observations. GNSSR estimates sea level height from the phase center antenna using the reflection of the extracted GNSS signal at sea level. With a large number of tidal stations equipped with GNSS antennas, GNSSR has the potential to be implemented in Indonesia. GNSSR observations can also cover sea surface areas tens to hundreds of kilometers away from where the antenna is located in coastal areas. Furthermore, the installation of a GNSS antenna at a safe height on land allows for the observation of sea levels during extreme conditions such as storms and cyclones. To employ GNSSR effectively, several factors must be considered, including signal-to-noise ratio (SNR) data analysis, data processing, filtering control variables, and increased frequency extraction. This study will focus on increasing temporal resolution by identifying the best control variables for each study area. This study used three months of GPS and GLONASS satellite SNR data from two stations, Barus and Morotai. The separated multipath data is then analyzed using the Lomb-Scargle Periodogram (LSP) based on its spectral frequency. The results of GNSSR sea surface height observations were validated using tide gauge data from both stations. Based on the test results, the RMSE values were 8.7 cm at the Barus station and 8.4 cm at the Morotai station. When GNSS-R results are compared to tide gauge data, they show a high correlation, with 0.955 at the Barus station and 0.982 at the Morotai station. Furthermore, the residual vector values from the comparison of the main tidal constants (K1, O1, S2, and M2) from tidal and GNSSR sensor data show relatively small values, namely less than 10 cm at both stations. Based on these findings, the GNSSR method can be used to complement tidal sensor data by applying proper quality control.
