以衛星及地面資料探討台灣高程系統

Abstract

基於台灣地區的高程系統，是以基隆驗潮站之平均海水面作為 正高起算面的零點。今以水尺及水準觀測配合驗潮站之潮位記錄值 ，率定基隆平均海水面與台灣高程基準點間之相對高程，其中，平 均海水面每年上昇0.16mm(依1971-1989年之年平均潮位值之變化量 )，高程基準點每年上昇1.34mm(於全球海水面上昇率1.5mm/yr之假 設情況下 )。因此，將來重測一等水準網時，應考慮此地殼垂直變 動率。 另配合IGS在台灣的測站，以 GPS測定6個驗潮站之ITRF地心座 標，並以衛星測高資料、 GPS觀測成果及本研究所採用的大地起伏 模式EGM96，求得6驗潮站的海水面地形(SST)，進而求得5個驗潮站 相對於基隆驗潮站之平均相對 SST值，此相對SST值除可顯示該等5 個驗潮站之平均海水位非處於同一等位面外，另可用於台灣一等水 準網加權約制平差模式之條件中，且其平差後之結果，恰反應實際 之地殼垂直變動。經比較各種不同之平差模式後，本研究成果顯示 ，在平差水準網中選定幾個控制點作為加權約制條件之模式，可適 用於未來台灣一等水準網整體平差。 The mean sea level (MSL) of the Keelung tide gauge is used to define the zero orthmetric height of Taiwan's height system. The relationship between the MSL of Keelung and the vertical datum's original point of Taiwan has been calibrated using a electronic device, differential leveling and tide records. According to the changes of yearly averaged tide records during 1971-1989, a trend of 0.16mm/yr (uplift) of Keelung MSL was found. Over that period the original point of vertical datum of Taiwan has been changed secularly at 1.34 mm/yr (uplift). The rate of vertical crustal motion must be considered when re-measuring Taiwan's first order leveling net. Using the GPS data from the IGS station in Taiwan and the IGS orbit, the geocentric coordinates in ITRF of the six key tide stations around Taiwan Island were determined. Satellite altimetry data, GPS and a geoid model have been used to determine the sea surface topography (SST) of the six tide stations. The mean SST at the five tide stations relative to Keelung were also computed. The relative SST reveal the fact that the MSL at these tide stations do not lie on the same equipotential surface. The relative SST at tide stations were then used as weighted constraints in the adjustment of Taiwan┬ first-order leveling net. and tht result reflects the vertical crustal motion of some benchmarks. The model of weighted constraints is recommended for furture adjustment of Taiwan's leveling net.