NASA - National Aeronautics and Space Administration

We distinguish between geocenter location and geocenter motion for their different purposes: precise orbit determination (POD) and earth surface mass variation monitoring. We present a method to measure the geocenter location through GPS tracked low earth orbiters (LEO) POD. We propose two methods to apply these geocenter location estimates to earth surface mass variation study. 19 years of daily geocenter locations in IGS14 reference frame are estimated from the POD of GPS tracked LEOs. These estimates are applied to 296 globally distributed GPS ground stations measured in the same reference frame for surface mass variation inversion. The results show that such determined geocenter location reaches sub-millimeter precision in each component judged by RMS of the overlapping differences. The geocenter motion change measured using the 80-station GPS orbit and clock product shows similar annual variation to the degree-1 term of the surface mass variation spherical harmonics determined from the 296-station inversion.