Determination Of CHAMP's Orbit And Earth Gravity Model From Onboard GPS Data

The satellite orbit determination is the key to the executive of satellite mission. The earth gravity field is the main force source for the satellite's motion in its orbit so that the satellite tracking observations can provide more information of the earth gravity filed. Refinement of earth gravity model can improve t ic accuracy of orbit determination of satellite. Therefore, the satellite orbit determir ation and the earth gravity model supplement each other.CHAMP is a German mini-satellite mission used to study on the earth science, atmosphere and their application, one of which is to precisely determine the global static long-wave-length characteristics of earth gravity and its temporal variations. So the precise orbit determination of CHAMP must be made from onboard GPS phase data. Centering on these hot spots of international geo-science studies, the main works and contributions in the dissertation include as follows.1. Development and applications of gravimetry and satellite-borne gravimetry are reviewed. Relations among the rectangle coordinates, Keplerian elements, Hillian elements and Equinoctial elements to describe the motion of low earth orbit satellite are given. The Hillian elements and the Equinoctial elements can solve the calculation problems because of the orbit singular. The perturbed motion of low earth orbit satellite is analyzed and the perturbed models a~e given in the dissertation.2. Based on the differential equations of satellite motion, the satellite orbit determination is discussed from the satellite tracking obseivations. The analytic method and the numerical integration method in the satellite crbit integration are analyzed. Then the multi-step Cowell II numerical integration formulae of satellite orbit integration are concluded.3. The preprocessing of onboard GPS phase data is studied. The polynomial fitting method to correct the clock error of onboard GPS phase data is discussed. The wide-lane and narrow-lane method and the successive difference method are used to solve the ambiguity and to detect and remove the cycle slip. In the meantime, the satellite attitude determination method, the tracking point correction model of GPS observation, the phase center correction and tre phase center offset correction of GPS antenna are analyzed. Soon afterwards, GPS phase data of CHAMP and IGS tracking stations are processed. The clock error is up :o ms level. The cycle slips of onboard GPS phase data of CHAMP are more than these of IGS tracking stations and it is more difficult to solve the ambiguity of onboard GPS phase data than these of IGS tracking stations. The phase center correction and the phase center offset are up to cm level, extremely to dm level.4. To determine the precise orbit of satellite and refine the earth gravity model, onboardGPS phase observations, single difference observation between satellites, air-ground double difference observation and air-ground triple difference observation are constructed from GPS data of IGS tracking stations and CHAMP.5. The problem of parameter estimation to determine the satellite orbit and solve the earth gravity model is analyzed. The partitioned Bayesian least squares parameter estimation is concluded. Then the observation equation, the variation equation and the derivatives of GPS observation are given in the dissertation.6. According to the satellite dynamical theory, the CHAMP orbit is determined from the air-ground double difference observations formed by GPS phase data of CHAMP and IGS tracking stations. Comparing with the PSO of GFZ in Germany, the radial accuracy of the orbit results is 0. 2857m. Comparing and analyzing the overlapping orbits, the radial accuracy is 0.0958m. Comparing the orbit ends, the radial accuracy is 0.0666m.7. Based on the satellite dynamical theory, an earth gravity model up to 70 degree, called as GGMOIS, is solved with the two-step method from one month of geometric orbit data of CHAMP. Comparing with EGM96 up to 70 degree, the geoid undulation accurac...