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Zusammenfassung:
The origin of the International Terrestrial Reference Frame (ITRF) is defined as the long-term mean center of mass of the total Earth system. Providing reliable and consistent estimates of geocenter motion improves the integrity and accuracy of geodetic solutions. The accuracy of the determination of the geocenter motion by individual measurement techniques is an indicator of their performance in terms of the realization of the ITRF origin. In this study, we analyze geocenter motion time series derived from the combined and individual analysis center solutions of the 3rd data reprocessing campaign (repro3) of the International GNSS Service (IGS). We estimate geocenter motion twofold: from the network shift approach and based on the inverse GNSS methods. In an inverse approach, we estimate low-degree (up to degree 5) spherical harmonic coefficients of surface mass redistribution to determine load-induced crustal deformations. We evaluate the estimated geocenter motion in terms of noise content, long-term trends, periodic and aperiodic variations and compare them with independent estimates from satellite laser ranging. The results show that for the periodic variations, a dominant periodic signal is observed with a period of approximately one year in all solutions. The amplitude of the annual signal is in the range of 1-4 mm, whereas the phase shows a slight variation. The periodic signal can be attributed to the effect of seasonal changes in surface mass distribution, such as variations in ocean mass due to the cyclical change in tides and changes in the water storage in large river basins.
