利用GPS載波相位求解衛星加速度及其應用

Abstract

GPS 被廣泛的應用在各種研究上，例如測量、導航、定時、地球物理及全球變遷等。本研究為 GPS 的另一應用，即利用 GPS 的載波相位加速度求解衛星的加速度。而衛星的加速度乃地球重力場的梯度，因此可由加速度反求重力場。目前，以 GPS 相位求解加速度的研究已經成功的被應用在地面上，惟在衛星高度上的研究則未見相關參考文件，而且也存在許多問題。在本研究中，吾人發展了一套利用 GPS/MET 的 GPS 相位觀測資料求解衛星加速度的方法，並且利用求得的加速度計算地位係數。本研究的數值實驗結果顯示： (1) 相位法對於衛星軌道的誤差並不敏感、 (2) 經過一次差分的相位求得的加速度較未差分相位之結果為佳、 (3) 相位法求得之加速度與真值 (利用數值微分法解得者) 之差值的 RMS 在 100 mgal 的數量級、 (4) 由加速度解得之地位模式反應出的重力趨勢與 EGM96 製造者相似。

Global Positioning System (GPS) has been widely used in many areas such as surveying, navigation, timing, geophysical research and global change studies. This study explores another use of GPS by deriving satellite's positional accelerations from GPS phase accelerations. Satellite accelerations are explicit functions of earth's gravity field, thus allowing gravity recovery. Currently, study of GPS phase-derived accelerations has been conducted near the ground, but not at satellite altitude, where more problems exist than the former. In this study, we have developed a procedure to compute GPS/MET's accelerations from its GPS phase observations, and to compute geopotential coefficients from the accelerations. The results of our numerical experiments show that : (1) the method is insensitive to satellite orbit error, (2) use of single-differenced phases produces a better result than the use of non-differenced phases, (3) the RMS difference between the phase-derived accelerations and the true ones (as derived from numerical differen-tiations) are on the order of 100 mgals, and (4) the recovered coefficients from the accelerations result in gravity patterns similar to those produced by EGM96.