台灣GPS連續觀測站高程變動受環境因子影響之研究; The Influence of Environmental Factors on the Vertical Deformation of Continuous GPS Stations in Taiwan

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Title:	台灣GPS連續觀測站高程變動受環境因子影響之研究;The Influence of Environmental Factors on the Vertical Deformation of Continuous GPS Stations in Taiwan
Authors:	陳建全;Chien-Chuan Chen
Contributors:	地球物理研究所
Keywords:	全球定位系統;週期;環境;連續觀測;高程;vertical;variation;environmental;period;GPS;continuous
Date:	2003-06-28
Issue Date:	2009-09-22 09:54:28 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	近年來GPS測量廣泛被應用在地球科學的研究上，研究結果顯示造成地殼變形的因素主要為板塊運動之外，環境因子的影響亦提供了一部份的變化，尤其對於高程方面影響更為顯著。而台灣為一海島，部分GPS連續觀測站也位於海邊或小島上，易受到潮汐、氣溫、氣壓、地下水位改變等環境因子的影響。因此本研究使用中央研究院及內政部GPS連續觀測站1994年至1999年中之高程資料，並配合中央氣象局數個觀測站之氣象觀測資料及經濟部水資源局設立之老埤站的地下水位記錄，藉由多元迴歸分析過程，求得環境因子影響之迴歸模型。本研究方法有三：(1)將各GPS連續觀測站高程資料以不同所屬單位及五個地理分區分組後，利用主成份分析法求得高程變化之各模式，觀察各站高程於時間上的變動行為。(2)利用快速傅立葉轉換分析方法，將各GPS連續觀測站高程資料由時間域轉換至頻率域，以瞭解各站高程週期性的變化。(3)由於GPS受環境因子影響的問題複雜，所以欲達到量化的估計環境因子對於GPS資料的變化的影響，必須盡量完整的考慮到會影響GPS資料的因素，所以先使用統計檢定測試個別環境因子對高程影響的顯著度，在以多元回歸分析的觀念，以向前選取法來建立較完整之環境因子影響模式，藉以瞭解環境因子與GPS高程的關係。研究成果顯示：(1)利用主成份分析方法有助於解析出GPS連續觀測站高程資料中較長週期性的變化模式，除了北部地區因站數太少，以致於各模式無明顯週期性變化之外，其餘中研院、內政部所屬站及東部、西部地區的第二及第三模式中皆呈現近乎「年」週期的變化，而南部地區則顯現「半年」週期的變動行為，且年週期性變動的振幅較半年週期大。(2)快速傅立葉分析方法則受到資料累積長度的限制，無法分析較長週期的訊號，但在較短週期有很高的解析力。結果顯示在約14天及28天週期有強訊號出現，但在YMSM、S101及S104三站不見28天週期的強訊號。綜合各站之迴歸分析結果，顯示影響高程之環境因子大小依序為Sa潮汐、氣溫、Mf潮汐、氣壓、相對濕度、Ssa潮汐、降水量及Mm潮汐。由地下水變化對S23R影響不大的結果，表示可能並非第一層地下水即可代表地下水荷重影響，還必需考慮更詳盡的影響來源。各站高程受Sa、Ssa、Mm、Mf潮汐影響之平均振幅為4.56、3.39、2.19、5.46 mm，顯示GPS資料處理過程中雖引入全球模式對海洋潮汐加以修正，但仍存在區域性海潮效應的影響。氣壓與氣溫變化對測站高程的平均影響量為 -0.40 mm/mb及0.44 mm/℃。推論可能與為大氣荷重效應及與混凝土柱、建築及土壤的熱膨脹有關；相對濕度及降雨量對高程之平均影響量為0.12 mm/％及0.03 mm/mm，相較於其他環境因子相對濕度及降雨量的影響量偏小，於台灣西南部地區甚至無影響，顯示使用附加參數修正對流層延遲誤差已獲得良好的成效。本文所討論的地球物理因素並非完全，往後因測量精度的提高及新設之連續觀測站不斷累積資料，將有助於發現其他潛在因子的影響以利建立更精確的修正模式。 GPS (Globe Positioning System) is widely used to measure crustal deformation in recent years. Besides tectonic movement, environmental factors also contribute a considerable portion of measured deformation. The influence of environmental factors on altitude variation is significant. Especially, Taiwan is an island easily affected by tides, air temperature, air pressure and water-storage loading etc. The surveyed altitude data with continuous GPS stations built by IES (Institute of Earth Sciences in Academia Sinica) and MOI (Ministry of Interior) from January 1994 to middle of 1999 were used in this study.10 local weather observation stations that are adjacent to the GPS stations we also collected. Additional, we used ground water leveling data of Laupi to analyze if height of S23R is affected by ground water change. We apply three different methods to understand the relationship between continuous altitude variations and environmental factors. (1) We separated data into IES, MOI and five local regions then employed PCA (Principle Component Analysis) to understand principle modes of height variation in time series. (2) We employed FFT (Fast Fourier Transform) to know cycling change of each station. (3) First, we used simple regression and statistic test to interpret influence of particular factor. Then we employed forward selecting and MRA (multiple regressions analysis) to build up the influenced model of environmental factors. Conclusion of this study can be summarized as follows: Except in north region, annual and semiannual period can be analyzed in GPS height variation by PCA. Because data lengths are not long enough, we can only detect 14, 28 days and else smaller than 200 days periods signal by FFT. Approximately, the effect of environment factors listed according to magnitude include Sa tide, air temperature, Mf tide, air pressure, relative humility, Ssa tide, rainfall and Mm tide. Average amplitude affected by Sa, Ssa, Mm, Mf tides are 4.56, 3.39, 2.19, 5.46mm, respectively, and 0.44mm/℃, -0.40mm/mb by air temperature and pressure. It means ocean tide correction still is not enough either in island or near coast. Concrete, soil thermal expansion and atmosphere loading may cause vertical displacement. There are other geophysical sources that are not considered in this study should be investigated in future.
Appears in Collections:	[Graduate Institute of Geophysics] Electronic Thesis & Dissertation

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