TRF Kinematics From Satellite Laser Ranging.

The continuous redistribution of mass within the Earth system causes concomitant changes in the Stokes coefficients describing the terrestrial gravity field. Seasonal changes in these coefficients have been closely correlated with mass transfer in the atmosphere, hydrosphere and oceans. The origin of the Terrestrial Reference System (TRS) is realized through the adopted coordinates of its defining set of positions and velocities at epoch, constituting the conventional Terrestrial Reference Frame (TRF). Its stability, integrity and applicability are directly related to the accuracy and fidelity with which such motions can be observed or modeled during the position determination of these sites. Since over two decades now, these site coordinates are determined through space geodetic techniques, in terms of absolute or relative positions of the sites and their linear motions. The new gravity-mapping missions, CHAMP and GRACE, and to a lesser extent the future mission GOCE, address directly the temporal gravitational changes. For the very low degree and order terms, there is also a geometric effect that manifests itself in ways that affect the origin and orientation relationship between the instantaneous and the mean reference frame, as well as the axes of figure orientation. Satellite laser ranging (SLR) data to LAGEOS 1 and 2 contributed in this effort the most accurate results yet, demonstrating millimeter level accuracy for weekly averages. Other techniques, like GPS and DORIS, have also contributed and continue to improve their results with better modeling and more uniformly distributed (spatially and temporally) tracking data. Improvements in the analysis methodology and the underlying models, resulted in a new series of weekly results, consistent with the recently adopted IERS Conventions 2003, and using the latest improvements in modeling SLR observations. We will present our results from several years of LAGEOS 1/2 and ETALON 1/2 SLR data, assess their accuracy and compare them to results from the various other techniques and geophysical monthly series from missions such as GRACE. A comparison of the SLR-derived trajectory of the "geocenter" with respect to the TRF, reveals a strong correlation with the geophysical events.