利用全球導航衛星系統干涉反射技術建立臺灣高程基準之可行性評估

The Feasibility Assessment of Defining Taiwan’s Vertical Datum using GNSS-IR Technique

本研究評估利用全球導航衛星系統干涉反射技術（Global Navigation Satellite System Interferometric Reflectometry，GNSS-IR）建立臺灣高程基準之可行性。以高雄港共站GNSS與潮位站資料為研究對象，分析2005年至2016年間之觀測資料。首先利用GNSS訊噪比（Signal-to-Noise Ratio，SNR）資料進行反射面高度反演，並透過精密單點定位（Precise Point Positioning，PPP）解算天線橢球高，進而推估海水面橢球高。為提升反演精度，本研究考慮海水面動態變化、對流層折射及GNSS頻間偏差等誤差改正，並結合潮汐調和分析輔助頻譜分析。結果顯示，GNSS-IR所推估之海水面橢球高與潮位站觀測具有高度一致性，其變化趨勢相關係數達0.87，線性迴歸斜率為0.99，決定係數（R2）高達0.9999，顯示GNSS-IR技術能有效監測海水面變化。然而，兩者之間仍存在-12.7 cm之系統性基準偏差。此差異最可能源自於垂直方向系統性誤差及海況偏差，惟兩者對總體偏差之貢獻程度仍有待進一步探討。整體而言，在扣除基準差異後，GNSS-IR於動態海水面監測上展現良好一致性與穩定性。本研究結果證實，GNSS-IR技術具備推估長期平均海水面橢球高之能力，並可作為潮位站觀測之補充，甚至在觀測稀缺區域具備替代潛力，對於未來高程基準現代化具有重要應用價值。

This study evaluates the feasibility of using Global Navigation Satellite System Interferometric Reflectometry (GNSS-IR) to establish Taiwan’s vertical datum. The co-located GNSS station and tide gauge at Kaohsiung Harbor were used, covering observations from 2005 to 2016. GNSS signal-to-noise ratio (SNR) data were analyzed to retrieve reflector heights, and Precise Point Positioning (PPP) was applied to estimate antenna ellipsoidal heights, enabling the derivation of ellipsoidal sea surface heights. To improve retrieval accuracy, several error sources were considered, including sea surface dynamics, tropospheric refraction, and inter-frequency bias. In addition, tidal harmonic analysis was incorporated to constrain spectral peak identification in the Lomb–Scargle periodogram (LSP). The results show strong agreement between GNSS-IR and tide gauge observations, with a correlation coefficient of 0.87, a regression slope of 0.99, and a coefficient of determination (𝑅2 ) of 0.9999. These findings indicate that GNSS-IR effectively captures sea level variability. However, a systematic datum offset of -12.7 cm was observed between the two datasets. The most likely sources of this discrepancy are systematic vertical-related errors and sea state bias, although their respective contributions require further investigation. Overall, after accounting for datum differences, GNSS-IR demonstrates high consistency and reliability in monitoring sea level variations. The results confirm that GNSS-IR is a promising technique for estimating long-term mean ellipsoidal sea surface height and can serve as a complementary or alternative observation method to tide gauges, especially in regions with sparse observations.