絕對重力監測點作為臺灣重力基準之研究

Study on Absolute Gravity Monitoring Stations for Taiwan Gravity Datum

1971年國際重力基準網（I.G.S.N.71）以多點基準取代單點1909年波茨坦重力基準，至現在正著手建置高精度（± 10 ìGal或更好）的國際絕對重力基本網（IAGBN），其主要任務是長期監測重力隨時間的變化，其次是作為重力測量的基準，及不同重力儀比對。因此，這些絕對重力點建立後，間隔數年後須進行重複觀測。內政部自2003年陸續購置兩部絕對重力儀FG5，在臺澎金馬地區（含蘭嶼及綠島）設置絕對重力監測點，實施絕對重力量測，作為重力測量引測重力之用。為此，2005年曾將絕對重力儀FG5運至巴黎國際度量衡局（BIPM），參加國際絕對重力儀比對活動（ICAG-2005），評估量測不確定度，藉以確保我國絕對重力量測能力與國際水準一致。而本文參考國際標準組織（ISO）量測不確定度表示指引，評估絕對重力監測點在95%信賴水準及擴充因子2.0下，其擴充不確定度約8 ìGal，預期可成為國際絕對重力基本網（IAGBN）之一，並作為國家重力基準及國家重力系統之主要依據。 The International Gravity Standardization Net 1971 (I.G.S.N.71) with more gravity datumhas been used to replace the Potsdam gravity system 1909 with only one basis. TheInternational Absolute Gravity Basestation Network (IAGBN) with high precision (± 0.1 ìms-2 or better) is scheduled to be established. The main purpose of the network is to monitortemporal gravity changes. Besides, the stations of the network are able to be served as a basisof regional gravity surveying and to function as reference stations for tests and comparisons of different gravimeters. Therefore, the stations of the network are required to be measuredrepeatedly at a certain interval.Ministry of Interior has owned two absolute gravimeters of FG5 since 2004. Theabsolute gravity monitoring stations measured with them have been carried out overthe area of Penghu, Kinmen, Matsu, Lanyu, Green Island and Taiwan for these years, which are serving as a basis for relative gravity surveying. For the quality assuranceprogram, the team with the Absolute Gravimeter FG5-224 in the name of ChineseTaipei took part in the ICAG-2005 campaign at BIPM in Paris for verifying themeasurement uncertainty of the absolute gravity. The result showed that ourcompetence in absolute gravity measurement is identical to the international level. Theexpanded uncertainty of the absolute gravity monitoring stations are evaluated to bearound 8 ìGal, in accordance with the “Guide to the Expression of Uncertainty inMeasurement” published by ISO and under the confidence level of 95% and coveragefactor of 2.0. Those stations are expected to act as a part of the IAGBN and the gravitydatum for the National Gravity System in Taiwan.

The International Gravity Standardization Net 1971 (I.G.S.N.71) with more gravity datumhas been used to replace the Potsdam gravity system 1909 with only one basis. TheInternational Absolute Gravity Basestation Network (IAGBN) with high precision (± 0.1 ìms-2 or better) is scheduled to be established. The main purpose of the network is to monitortemporal gravity changes. Besides, the stations of the network are able to be served as a basisof regional gravity surveying and to function as reference stations for tests and comparisons of different gravimeters. Therefore, the stations of the network are required to be measuredrepeatedly at a certain interval.Ministry of Interior has owned two absolute gravimeters of FG5 since 2004. Theabsolute gravity monitoring stations measured with them have been carried out overthe area of Penghu, Kinmen, Matsu, Lanyu, Green Island and Taiwan for these years,which are serving as a basis for relative gravity surveying. For the quality assuranceprogram, the team with the Absolute Gravimeter FG5-224 in the name of ChineseTaipei took part in the ICAG-2005 campaign at BIPM in Paris for verifying themeasurement uncertainty of the absolute gravity. The result showed that ourcompetence in absolute gravity measurement is identical to the international level. Theexpanded uncertainty of the absolute gravity monitoring stations are evaluated to bearound 8 ìGal, in accordance with the “Guide to the Expression of Uncertainty inMeasurement” published by ISO and under the confidence level of 95% and coveragefactor of 2.0. Those stations are expected to act as a part of the IAGBN and the gravitydatum for the National Gravity System in Taiwan.