Gravity Model Induced Systematic Errors in Reference Frames

Abstract

Terrestrial reference frames realized by diverse satellite techniques and estimated through various Analyzing Centers show systematic differences in scale, origin, direction and rate of rotation axis, which are at the cm-level. One of the error sources is the uncertainty in the gravity field, including the adopted gravitational constant GM value. The sensitivity of the scale of an SLR frame to the relative error in GM is about 0.62, when tracking data to LAGEOS are used. If the frame is estimated from SLR measurements to GPS satellites, the sensitivity factor would have been increased to about 1.4, since the scale effect increases with the altitude of the satellite. But for GPS microwave-tracking data the scale sensitivity to the GM error is reduced to about 0.07 ! The reason is that the GPS is an one-way tracking technique, no reflector is needed, but two clocks are required. The errors in GM and the gravity model are largely absorbed in the double differences, or in the clock estimates. GM and gravity model errors are important for SLR, DORIS and PRARE techniques, but not for GPS. The ppb-level scale error in the GPS reference frame could result from the errors in the satellite antenna phase center offsets.