Inversing Geocenter Motion Based On Surface Load Theory

Since the 1980s, it has become a reality to establish and maintain a global/regional geocentric coordinate system as the rapid development of the space geodetic techniques(VLBI, SLR, LLR and DORIS etc.), particularly the maturity of the global navigation satellite system (GNSS) technology. The origin of the geocentric coordinate system is located at the center of the ellipsoid earth (geocenter). The ellipsoid axis points to the agreement terrestrial pole, the initial geodetic meridian plane coincides with the zero meridian plane, x and z axis direction is set by some epoch of EOP, x?y and z axis constitute a right-handed cartesian coordinate system in space.Because of the complexity of the movement and deformation occurring on the Earth, we can only establish and maintain a certain precision of the terrestrial reference frame by simulating and correcting some major and regular factors at a certain level[1]. The maintenance of the high precision geocentric reference frame such as ITRF needs to take the maintenance of plate movement (mainly along the horizontal direction), postglacial isostatic adjustment of the crust (mostly along the vertical direction), crust tectonic deformations, changes in surface loads and geocenter motion in to consideration.The barycenter of the earth (hereinafter referred to as the geocenter) is the mass center of the whole earth system CM (center-of-mass), including the solid earth and the liquid layer covered on the solid earth surface (ocean, atmosphere, rivers, lakes and glaciers etc.). Geocenter motion is mainly caused by the material motion of various layers of the Earth, the seasonal variation of the global atmosphere, marine and land surface water is the major geophysical mechanism of annual geocenter motion, so we can invert the annual motion of geocenter from these seasonal variations of the geophysical factors. In addition, geocenter motion also has a long-period component, this is caused by postglacial isostatic adjustment of the crust. The origin of the geocentric coordinate system is defined at the geocenter, the coordinate of the surface sites is fixed relative to the geocenter's position, so the change of the geocenter is bound to result in the change of the coordinate of surface sites, and geocenter motion will be the major factors which should be taken into consideration in the course of the maintenance of the dynamic geocentric reference frame.This thesis is based on the surface load theory, respectively uses IGS which provides the displacement of IGS05 framework sites of global range, ECCO model which provides ocean bottom pressure data by 1.0°×1.0° resolution of global range and NCEP which provides atmospheric load data by 2.5°×2.5° resolution of global range, to study the solid Earth deformation caused by the changes of surface mass load, and the surface gravity changes by this, and then acquires recent geocenter time series of 10 years and 12 years, search the cycle of geocenter motion by using power spectrum analysis methods, and finally fits the amplitude and phase of the geocenter motion cycle respectively.