台灣重力網平差及重力資料應用

Abstract

本研究利用聯勤測量隊進行全省重力網量測之觀測量組成觀測方程式，再以加權約制平差求解重力網中各未知重力點的絕對重力值，平差結果的後驗中誤差為+-0.020 mgal，各未知重力點中誤差估值為0.1∼0.3mgal。將收集之陸上重力經過約化、改正，船測重力經過平差和測高資料經過修正後，以進行下列之應用：1.利用上述資料，以最小二乘配置法（Least-Squares Collocation, LSC）配合去除回一復法（Remove-Restore）和剩餘地形模式（Residual Terrain Model, RTM）理論計算出高精度大地起伏，並支GPS結合水準測量檢核其精度，結果證實計算之大地起伏平地可符合5mm√K二等水準測量精度要求，而高山可符合12mm√K三等水準測量精度要求。2.利用TOPEX/POSEIDON測高資料配合應用一計算之大地起伏求得交叉點處海水面地形（SST），然後以SST分析交叉點處短週期海流流況，結果發現夏季海流往北方流，冬季海流往南方流；若分別以平均後的測高資料計算交叉點海流，其流速約為41∼50 cm/sec，方向往西北。3.應用一所計算之精密大地起伏若結合GPS所測之橢球高和歷年公佈之一等水準點高程，即可監測臺灣地區地榖垂直變動，計算成果顯示出臺灣地區大部份區域呈現上昇狀態。

This study adjusts the gravity measurements collected by Base Survey Battalion using least - squares with constraints. The estimated instrument accuracy is 0.02 mgal and the error estimates of the gravity values at given gravity stations are 0.1 to 0.3 mgal. The adjusted gravity data are combined with existing land gravity data and shipborne gravity data. Together with altimeter data, the combined gravity data are used in the following studies: l. A geoid model of Taiwan is computed by least-squares collocation. The geoid model and GPS heights yield orthometric heights with accuracies of 5mm√K in flat areas which fulfills the second-order leveling accuracy requirement, and of 12mm√K in mountainous areas. 2. The sea surface topography (SST) values at one crossover of TOPEX/POSEIDON (near Bashi Channel) were computed using T/P cycles l to 183 data and the SST values were used to study the geostrophic currents at this crossover. In summer the currents flow northwards while in winter the currents flow southwards. The average speed is 41 to 50 cm/sec and the flow is in the northwest direction. 3. The geoid model and GPS ellipsoidal heights at 86 benchmarks measured in 1997 were used to compute modeled orthometric heights, which were compared with the orthometric heights measured 10 to 20 years ago. The differences show that almost all benchmarks undergo uplift in the past, mostly due to the collision between the Philippines Sea Plate and the Eurasia Plate.