| By the middle of this decade, measurements from the CHAMP (CHAllenging of Minisatellite Payload) and GRACE (Gravity Recovery And Climate Experiment) gravity mapping satellite missions are expected to provide a significant improvement in our knowledge of the Earth's mean gravity field and its temporal variation. For this research, new observation equations and efficient inversion method were developed and implemented for determination of the Earth's global gravity field using satellite measurements. On the basis of the energy conservation principle, in situ (on-orbit) and along track disturbing potential and potential difference observations were computed using data from accelerometer- and GPS receiver-equipped satellites, such as CHAMP and GRACE. The efficient iterative inversion method provided the exact estimates as well as an approximate, but very accurate error variance-covariance matrix of the least squares system for both satellite missions.; The global disturbing potential observable computed using 16-days of CHAMP data was used to determine a 50 x 50 test gravity field solution (OSU02A) by employing a computationally efficient inversion technique based on conjugate gradient. An evaluation of the model using independent GPS/leveling heights and Arctic gravity data, and comparisons with existing gravity models, EGM96 and GRIM5C1, and new models, EIGEN1S and TEG4 which include CHAMP data, indicate that OSU02A is commensurate in geoid accuracy and, like other new models, it yields some improvement (10% better fit) in the polar region at wavelengths longer than 800 km.; The annual variation of Earth's gravitational field was estimated from 1.5 years of CHAMP data and compared with other solutions from satellite laser ranging (SLR) analysis. Except the second zonal and third tesseral harmonics, others second and third degree coefficients were comparable to SLR solutions in terms of both phase and magnitude. The annual geoid change of 1 mm would be expected mostly due to atmosphere, continental surface water, and ocean mass redistribution. The correlation between CHAMP and SLR solutions was 0.6∼0.8 with 0.7 mm of RMS difference. Although the result should be investigated by analyzing more data for longer time span, it indicates the significant contribution of CHAMP SST data to the time-variable gravity study. (Abstract shortened by UMI.)... |
