| Summary: | 碩士 === 國立交通大學 === 土木工程系 === 88 === 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.
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