Assessing Tropospheric Delay on Monitoring Coastal Sea Level Changes from GNSS-R

  • 洪 紹倫

Student thesis: Doctoral Thesis

Abstract

Due to global warming the global mean sea level has risen rapidly in recent years causing many serious impacts especially in the coastal areas Thus monitoring coastal sea level changes is an important and hot topic In general the conventional methods to measure sea level variations are to use tide gauges and satellite altimetry; however tide gauge measurements are affected by vertical land motions and satellite altimetry observations in the coastal regions are inaccurate resulting from complex waveforms caused by land contaminations Recently signal-to-noise ratio (SNR) data from Global Navigation Satellite System (GNSS) have been demonstrated for measuring sea level heights This study use GNSS-Reflectometry (GNSS-R) SNR data to retrieve sea level heights by the method of Lomb Scargle Periodogram (LSP) aided with tidal harmonic analysis and the results are compared with the nearby traditional tide gauges In addition the tropospheric delays would cause errors in sea surface heights from GNSS SNR data so two different tropospheric corrections are applied including refraction correction and tropospheric model correction In this study the data from two GNSS stations at Chittagong site in Bangladesh and Heping site in Taiwan with different tidal ranges and surroundings are used The result in Chittagong station shows the standard deviation (STD) of differences is 30 4 cm and the correlation coefficient is 0 97 while the result in Heping station shows the STD of differences is 12 8 cm and the correlation coefficient is 0 96 The clear elevation-dependent errors observed in Chittagong station are probably from tropospheric delays After applying the refraction correction the STD in Chittagong station is reduced from 30 4 cm to 28 1 cm Moreover after applying the tropospheric model correction the STD in Chittagong station decreases from 30 4 cm to 29 4 cm However the elevation-dependent errors in Heping station is small It may result from that the tidal range is small or the other larger errors are not corrected so the tropospheric correction is limited
Date of Award2019
Original languageEnglish
SupervisorChung-Yen Kuo (Supervisor)

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