Studies of the Earth's center of mass periodical movements

Abstract

At present the Earth reference coordinate frame ITRF is realized on the base of space geodesy observations in strictly secular sense with purely linear temporal changes (velocities) without any conventional models. These linear changes include primarily non modeled geophysical motions, mostly of tectonic origin. In the base of all space geodesy techniques (except of VLBI), there are precise orbits of the observable satellites, which are moving under the influence of the Earth gravity field around of the entire Earth’s center-of-mass (CM). To keep the convention of the coincidence of the terrestrial coordinate system origin with the entire Earth center-of-mass, the first harmonics (C1,1, S1,1, C1,0) of the gravity field models, used for orbital calculations, are equated to zero. Studies of the ITRF precision and stability, carried out at the different research centers, INASAN included, show that origin of the coordinate system (Geocenter) is moving relatively to the center of mass. Besides the main geophysical effects: atmosphere pressure, oceanic tides and currents, ice melting, have been taken into consideration. The annual and semiannual amplitudes of the geocenter variations are not the same for different types of measurements and fluctuate in the interval 1–23 mm for all three components of the position vector. And Z-component is always 2–3 times more than planar components. The absolute scale of the network is determined with the accuracy around of 0.5 · 10−13, that is equivalent 3 mm in the station height. The further improvement of the ITRF accuracy and stability is possible with the use of more dense and equally distributed tracking networks, equipped with the different types of modern instruments, allowed to minimize systematic errors, characteristic for every usable technique. In this connection the International Association of Geodesy arrived to a decision on the development of the Global Geodetic Observing System (GGOS), which will consist of about 40 permanent ground tracking sites, space segment of special research satellites and centers of merging, storage and analyses of the data.