An Updated Estimate of Geocenter Variation from Analysis of SLR Data

Abstract

The Earth’s center of mass (CM) is defined in satellite orbit dynamics as the center of mass of the entire Earth system, including the solid Earth, oceans, cryosphere, and atmosphere. The CM can be realized using the vector from the origin of the International Terrestrial Reference Frame (ITRF) to the CM, and directly estimated from satellite laser ranging (SLR) data. In previous studies and ITRF translations, SLR observations were assumed to contain only a constant, systematic, station-dependent bias. This treatment leads to a difference of a few mm between the SLR results and other estimates, such as GPS-based global inversions. We show that the difference cannot be attributed to the deficiency of the distribution of SLR tracking stations but is due to the impact of a significant surface-loading-induced seasonal signal captured in the laser range measurement (appearing in station range bias) during the traveling of the laser light pulse. The errors in the modeling of the troposphere zenith delay considerably impact the determination of geocenter motion from SLR data. The SLR-data-derived geocenter motion becomes comparable to the global inversion results when the range biases and thermosphere delay for SLR tracking stations in the SLR network are adjusted as part of the monthly solution.