| Summary: | 碩士 === 國立交通大學 === 土木工程系所 === 92 === With the CHAMP GPS phase data, GPS Prep. and GEODYN II are used in a dynamic method to compute CHAMP satellite orbits. The RMS differences in the X, Y, and Z directions between the computed orbits and the GFZ precise orbits are 1.454 m, 3.467 m, 2.925 m, respectively. In general, the accuracy of the computed orbits in this work is at the meter level. A two-step method with data from the Muenchen technical university of Germany is also used to calculate CHAMP satellite orbits and to estimate the earth’s gravity fields. The resulting gravity models are named NCTU models. Both geoid undulations and gravity anomalies from the NCTU models agree better with those from the GGM01S gravity model than those from the EGM96 model. This shows that the NCTU models outperform EGM96. Using one year of CHAMP satellite’s orbital data in a degree-5 solution and a degree-10 solution, the time-variations of J2, J3 and geocenter motions are obtained. The time-variations of J2 and J3 show secular and seasonal variations. The difference in geocenter motion from the degree-5 and degree-10 solutions is marginal.
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