Large-scale Time-variable Unified Gravity Field Model Using GRACE Data

We established a large-scale time-variable unified gravity field model IGG-TVG2013 based on GRACE satellite data from 2003 to 2012 using the least square method. This model is composed of annual and semi-annual trends and periodic terms, usually of each spherical harmonic coefficient. Besides those empirical parameters, an acceleration term, tidal aliasing error, and large earthquakes are taken into account. Acceleration is a modification to linear trend to detect and express more details in signals. Tidal aliasing error is the residual error in a tide model that must be carefully removed from GRACE solutions; a co-seismic jump in the gravity field may disturb the secular trend. An evaluation of IGG-TVG2013 solutions and corresponding GRACE solutions shows that the RMSE value in 92% of global grids was less than one ugal. Extrapolation results for the first half of 2013 using the IGG-TVG2013 model shows this model has good potential in short-term forecasting. We concluded that the IGG-TVG2103 model can effectively describe the time-space variability of gravity field.