Study On The GRACE Satellite Time-variable Gravity Field

US-Germany co-sponsored satellite Gravimetry mission GRACE (Gravity Recovery and Climate Experiment), launched in March 2002 has provide series of Earth gravity models with Spatial resolution of 200km and Temporal resolution of one month. Recovery of time-varying gravity based on GRACE'S monthly models will have profound impacts on studies in solid Earth geophysics, oceanography, climatology and geodesy.The main content of the paper is summarized as follows:(1) The analysis of GRACE gravity field model shows that, improvements relative to the gravity model EGM96 are clearly achieved below 90 degree. To some extent, GRACE gravity satellite has filled the gaps between the middle wavelength and long wavelength gravity signal.(2) The formula for gravity anomaly expressed by spherical harmonic coefficients has been systematically studied. This paper mainly introduced methods to calculate time-variable gravity. The errors from the high-degree of the GRACE gravity field accounts for main components. Gaussian Filtering has been used to denoise the errors. The election of the degree in gravity models has played an important role in whether gravity field can show the time-variable characters. The study shows that the monthly time-variable gravity can be explore by the GRACE'S models and shows the periodicity in a certain area and the erratically variety in local place. The time-varying gravity will have significance in studying the changes of the sea level ,continental water storage , redistribution of the air quality, and in studying geodynamic process such as earthquake and volcano triggering and plate motion.(3) The gravity anomaly in Wenchuan region has been calculated by using GRACE gravity field model. And give the qualitative analysis of abnormal condition and horizontal gravity gradient. At the same time, we using one week's and one month's time-varying gravity field models to calculate the seismic gravity changes of Wenchuan earthquake area, The results showed that ,after the Wenchuan earthquake the gravity changes from low to high.