CoAuthors

Jean-Michel Lemoine (CNES, France)

The gravity field model EIGEN-GRGS.RL03-v2.MEAN-FIELD has been selected for the new GDR-E standards. The model is complete to degree and order 260. It is based on GOCE data (i.e. EGM-DIR5 model) for the part between degrees 81-260. The time-variable gravity (TVG) coefficients for degrees 1 to 80 were obtained from a regression on the GRGS-RL03-v2 monthly time series (2002.5-2014.5). For degree 2 this TVG part was extended to 1985-2014.5 through the use of a GRGS SLR-only (Lageos+Lageos-2) solution between 1985 and 2003. Outside the measurements period (1985-2014.5 for degree 2, 2003-2014.5 for degrees 3 to 80), the gravity field is extrapolated with a zero-slope assumption. The modeling of the TVG part includes for the first time two annual and two semi-annual coefficients for each year, in addition to one bias and one drift for each year.
In this presentation we will explain how the model was constructed, describe the TVG coefficients that are included in the model, and discuss the zero-slope assumption that is used for extrapolation. Since this assumption is not satisfactory on the long term, we will propose a method for a regular update of the extrapolated part.