| Summary: | 碩士 === 國立成功大學 === 測量及空間資訊學系 === 107 === 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.
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