SLR CONTRIBUTIONS IN THE ESTABLISHMENT OF THE TERRESTRIAL REFERENCE FRAME

Abstract

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). Since over two decades now, these coordinates are determined through space geodetic techniques, in terms of absolute or relative positions of the sites and their linear motions. 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 the oceans. The new gravity-mapping missions, CHAMP and GRACE, and to a lesser extent the future mission GOCE, address these temporal changes from the gravimetric point of view. 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. 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. We present our operational methodology and results from our latest analysis of 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. A comparison of the SLR-derived trajectory of the “geocenter” with respect to the TRF, reveals a strong correlation with the recent geophysical events. The interpretation and comparison will benefit significantly from the future availability of geophysical series at higher temporal resolution and with more accurate content.