Dynamic model orbits and Earth system parameters from combined GPS and LEO data

Ground- and space-based GPS receiver observations together with non-GPS observations can be adjusted in an integrated solution estimating orbits and Earth parameters simultaneously in a dynamic model. Especially reference frame and low degree gravity field parameters profit in accuracy when compared to a solution where GPS ephemerides and clocks are separately estimated before treating the low Earth orbiters (LEOs). In this analysis, we integrate GPS constellation observations with CHAMP, GRACE and SAC-C data. Procedural problems are discussed as well as results concerning LEO orbit and Earth system parameter estimates. Based on 7 months of CHAMP data, time series of the geocenter location and the Earth's principal axes of inertia are computed and the results discussed. It turns out that the time series of the X and Y components of the geocenter and the orientation of the Earths' primary axis of inertia can be resolved showing geophysically meaningful sizes and frequencies.