Study On Variations Of The Earth's Rotation Using Gravity Data

In chapter 1 of this paper, the research methods and some measurement technologies for the variations of earth's rotation are simply introduced. The working principle of a superconducting gravimeter (SG) is described in detail.In chapter 2, the angular momentum equation and excitation function are introduced firstly; then the polar motion excitation from atmosphere, water and gravitation of the sun and moon is discussed.In chapter 3, the characteristics of the Earth's deformation and perturbation in gravity potential the under tidal gravity and polar motion are presented.In chapter 4, we present the preprocessing methods of the SG recordings. The power spectra and product spectra density of gravity data sets from four SG stations are calculated by using the auto-regression model. Finally, the amplitude factor and phase difference, parameters describing the Earth's deformation response to the perturbations of the centrifugal forces arising from polar motion, at Chandler period are accurately retrieved.The results indicate that main energy of gravity caused by polar motion is concentrated near the Chandler and annual periods. After stacking, the difference of the periods, evaluated from the SG data and from the polar motion data provided by the International Earth Rotation Service (IERS), is about 0.4% for the Chandler signals, and about 3.9% for the annual signals. It implies that SG observations can detect effectively the gravity change caused by polar motion. The gravimetric parameters of the Chandler wobble are accurately retrieved as 1.1613 (?. 0275) for amplitude factor, and -1.30 ( 1. 33) for phase differences. However, the results of annual polar motion are not acceptable because of the effects from the other global annual perturbations.