Title

利用測高衛星、重力衛星、NCEP 氣候模型估計地心與C20變動

Translated Titles

Geocenter and C20 variations derived by satellite altimeters, GRACE and NCEP climate model

Authors

陳盈樺

Key Words

地心變動 ; GRACE ; 衛星測高 ; geocenter ; GRACE ; altimeter

PublicationName

成功大學測量及空間資訊學系學位論文

Volume or Term/Year and Month of Publication

2009年

Academic Degree Category

碩士

Advisor

郭重言

Content Language

繁體中文

Chinese Abstract

地心變動為地球質量中心相對於地球幾何中心之移動,通常以一階球諧係數表示,此變動為地球系統中質量重新分配所造成,例如海洋、大氣、陸上水體、冰川、冰原間質量交換。前人採用衛星雷射測距、全球定位系統或衛星測高資料估計地心變動量,但缺點為測站分佈不均且僅位於陸地。另外,也有研究學者使用精度無法評估之氣候模型進行地心位置變動估計,而造成估計誤差無法評估。理論上,各階球諧函數呈現正交關係,因此估計一階項時,並不受到其他階係數影響,然而,Lavalle´e等人[2006]指出未精確模式之高階係數會混疊一階係數之估計。GRACE衛星自2002年發射後,已成功且持續提供月平均之全球重力場2~120階球諧係數解,但其中C20項精度不佳,故本研究視其為未知數進而求解。本研究結合改正steric sea level和地殼垂直變動後之衛星測高資料與GRACE重力場解進行地心位置與C20變動之估計。計算之地心變動其振幅與相位在x方向為1.2±0.2 mm和67.8±9∘,y方向為2.2±0.2 mm和337.1±4.7∘,z方向為2.5±0.3 mm和61.1±6.6∘,與Swenson等人[2008]計算之成果接近,而估計之 ΔC20其振幅與相位分別為1.1×10-10±1.2×10-12和38.7±6.9°,比GRACE觀測之ΔC20接近於SLR之結果。此外,於陸地上加入NCEP氣候模型(積雪、大氣壓力、土壤濕度資料)進行一階項係數與C20變動量估計,其結果並無明顯改善,可能原因為氣候資料誤差較大且無法預估。

English Abstract

Geocenter variations defined as the position of the Earth’s center of mass (CM) relative to the center of figure (CF) of the Earth’s outer space are caused by mass redistribution like the mass exchange between ocean mass, atmosphere, ice sheets, glaciers, and hydrology. In previous studies, geocenter variations were estimated using Satellite Laser Range (SLR)、Global Positioning System (GPS), or satellite altimeter measurements, but these measurements do not distribute globally and evenly. In addition, some researchers used climate models with unknown uncertainties to estimate geocenter, which causes the errors of estimated geocenter are not assessable. Theoretically, higher degree harmonics do not bias the estimate of degree one because they are orthogonal; however, Lavalle´e et al. [2006] reported that unmodeled higher degree harmonics could actually alias the estimate of geocenter variations. GRACE mission has been successfully and continually providing monthly average observations of the Earth’s gravity field since the satellites were launched in 2002. The observations are represented in form of 2~120 degree spherical harmonic coefficients, but the degree-2 coefficient is currently not well determined. In this study, we estimated geocenter and C20 variations accurately by combining the steric-corrected and loading-corrected altimeter data and GRACE solution to reduce the aliasing of higher degree harmonics to estimate geocenter variations. The annual amplitude of x-, y-, and z-components are 1.2±0.2mm, 2.2±0.2mm, and 2.5±0.3mm respectively. The annual phase of x-, y-, and z-components are 67.8±9o, 337.1±4.7o, 61.1±6.6o respectively. The computational result agrees well with Swenson et al. [2008]. Additionally, compared with GRACE-derived C20, the annual amplitude and phase of the estimated ΔC20 at 1.1×10-10±1.2×10-12 and 35.8±5.8o in this study are much closer to SLR-derived ΔC20. Finally, we join the NCEP climate model (snow, atmospheric pressure, and soil moisture data) to compute geocenter and C20 variations but the estimate is not significant improved because the error of the model may be large and not assessable.

Topic Category 工學院 > 測量及空間資訊學系
工程學 > 工程學總論
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Times Cited
  1. 戴郁伶(2013)。結合衛星雷射測距與衛星測高估計地心變動。成功大學測量及空間資訊學系學位論文。2013。1-84。 
  2. 鐘子淵(2012)。利用GRACE、測高資料、海洋模型估計地心變動。成功大學測量及空間資訊學系學位論文。2012。1-78。 
  3. 許廷安(2010)。GPS衛星之軌道預測。臺灣大學應用力學研究所學位論文。2010。1-96。