地心變動定義為地球質量中心 (Center of mass, CM) 相對於幾何中心(Center of figure, CF)之位置變化，一般以一階項之球諧係數表示。由於地心變動的為地球系統之質量重新分布，其反應出地球質量平衡及以及固體地球與地球系統中之質量交換。由於地心變動為地球質量之重新分布造成，因此透過質量變化之觀測量可精確地估計地心變動。本研究主要結合SLR及GRACE 提供之重力場解與衛星測高資料，透過Swenson 等人2008 年提出之演算法以及疊代計算方式估計地心變動，結果顯示疊代計算之成果發現使用疊代計算之成果精度較Swenson 等人[2008]提出之演算法精度更為提升，並將估計成果與使用不同資料計算之地心變動做比較。使用測高資料結合衛星雷射測距之重力場解亦可獲得相當於結合GRACE 資料相當之估計成果，顯示衛星雷射測距之重力場解亦可有效估計地心變動之情形。將估計之一階項變化量加入高階項係數計算海水質量，計算其相對於衛星測高觀測量之差值，結果顯示由GRACE 重力場解估計之一階項結合高階項係數計算成果最符合測高衛星之觀測成果，其次為衛星雷射測距重力場解
估計之成果。最後本研究加入衛星雷射測距自1993 年提供之重力場解估計長時間地心變動，以其影響量計算缺漏之一階項並結合GRACE 提供之高階項係數以計算地表之質量變化，結果顯示加入一階項後可影響計算之質量變化最大有50%之影響。於研究特定區域之質量變化發現，格陵蘭及南極洲之冰原質量以 -80.84±2.21 mm/yr 及-9.80±2.29 mm/yr 的速率下降，全球海水面則以0.72±0.15 mm/yr 速率上升。因流入裏海區之河水量漸少導致該區海水質量以17.52±1.83 mm/yr 速率減小。

Geocenter variation is defined as the displacement of the Earth’s center of mass (CM) relative to its center of figure (CF) and is generally represented as the temporal variations of degree 1 geopotential coefficients. Because
geocenter variation results from the mass redistribution within the earth system, it can be accurately determined if mass changes on the Earth are well known. In the present study, SLR and GRACE gravity field solutions combining with
steric-corrected altimetry are used to calculate the geocenter motions by the algorithm from Swenson et al. [2008] and the iteration algorithm. The results computed by the iteration algorithm agree well with those by the algorithm from Swenson et al. [2008] and even have higher precisions. The results derived from SLR and GRACE solutions combining with steric-corrected altimetry data are consistent, indicating that not only GRACE data but also
SLR geopotential solutions be used to estimate geocenter motions. The mass variations computed using the estimated degree 1 coefficients from GRACE combining with higher degree-order coefficients agree better with the steric-corrected altimetry measurements than from SLR; however, the
SLR-estimated geocenter motions cover a longer time span starting from 1993. Finally, the SLR-derived geocenter motions and GRACE gravity solutions were combined to calculate the mass changes. The results show that the
differences of the computed mass variations can change up to 50% of total mass changes in amplitudes when the estimated geocenter motions were used. The ice sheets in Greenland and Antarctica are melting at the rates of -85.38 ± 1.26 mm/yr and -10.54 ± 0.55 mm/yr, respectively, and global ocean
mass variations (within latitude ±66o) is rising at a rate of 0.72 ± 0.15 mm/yr.The ocean mass in the Caspian Sea is also decreasing at a rate of -16.61±1.37 mm/yr because of less river discharge.

陳盈樺，利用測高衛星、重力衛星、NCEP氣候模型估計地心與C¬20變動，國立成功大學測量及空間資訊學系碩士論文，2009.

鐘子淵，利用GRACE、測高資料、海洋模型估計地心變動，國立成功大學測量及空間資訊學系碩士論文，2012.

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