Coastal Sea Level Variations Derived from GNSS SNR Data - A Case Study in Taiwan

  • 李 啓民

Student thesis: Master's Thesis

Abstract

Global sea level rise (SLR) has caused many kinds of disasters damaging the lives and properties of numerous human beings especially in low-lying coastal regions Therefore understanding and monitoring coastal sea level variations are of great importance for human society This research used Global Navigation Satellite System (GNSS) signal-to-noise ratio (SNR) data from the GNSS stations located in Taiwan (Kaohsiung Suao and TaiCOAST) and Sweden (Onsala Space Observatory OSO) to compute sea level heights (SLH) by using three different methods including Lomb Scargle Periodogram (LSP) aided with tidal harmonic analysis LSP-only and inverse modeling (IM) The GNSS-derived sea level variations are compared with those from co-located or nearby traditional tide gauges In Taiwan the GNSS-derived sea level variations in Kaohsiung and Suao show good agreement with those from tide gauges with the standard deviations (STDs) of differences ranging from 7 1 - 11 1 cm and the correlation coefficients of 0 94-0 97 In addition more than 80 % of SLH can be successfully achieved during the SNR available periods Besides the absolute sea level trend in Kaohsiung during 2006-2011 calculated by combining the vertical motion and the relative sea level from GNSS is mm/yr which agrees with that derived from satellite altimetry of mm/yr However this comparison is not robust because the uncertainty is almost the same level with the estimate resulting from the short time coverage of data In contrast merely 40 % of SLH can be successfully provided by TaiCOAST and the STD of differences between GNSS-derived and tide gauge sea level changes is 1 12 m with a correlation coefficient of 0 13 TaiCOAST has poor performance for monitoring sea level changes since the GNSS signals may be reflected from intertidal zone when sea level ebbs On the other hand the GNSS-based tide gauge in Sweden can offer over 90 % of SLH by both LSP and IM methods The STD of differences between sea level changes derived from GNSS SNR by IM and the tide gauge decreases about 2 cm compared with that by LSP and the correlation coefficient increases from 0 91 to 0 97 From the bottom line the GNSS stations in Taiwan except for TaiCOAST demonstrate the potential of serving as GNSS-based tide gauges to measure sea level changes like a specially designed one (e g OSO) does
Date of Award2017 Aug 29
Original languageEnglish
SupervisorChung-Yen Kuo (Supervisor)

Cite this

'