# Update of the EIGEN time variable gravity model for precise orbit determination

**CoAuthors**

**Event: **2017 Ocean Surface Topography Science Team Meeting

**Session: **Precision Orbit Determination

**Presentation type: **Type Oral

Precise orbit determination is a key element in the overall accuracy of the altimetric measurements. Since 2002, thanks to the GRACE mission, we have now an amazing - as some would say - knowledge of the Earth gravity field and its time evolution. Based on 28 years of LAGEOS data, 12 years of GRACE data and 3 years of GOCE data, the EIGEN-GRGS.RL03-v2.MEAN-FIELD is the gravity model that is used for the GDR-E standards. It contains a time-variable gravity (TVG) part until degree and order 80, and a static part coming from the model GOCE-DIR5 up to degree and order 300. The TVG part is modeled for each year between August 2002 and June 2014 as an annual bias + slope + annual and semi-annual periodic components. For degree 2, the TVG part extends from January 1985 to June 2014 thanks to the contribution of the SLR satellites.

In order to closely follow the actual evolution of the Earth gravity field and to maintain the accuracy of the POD over medium and long time scales, this model has been updated by adding two more years of GRACE measurements until July 2016 and by increasing the TVG maximal degree to 90.

We will discuss the inclusion of the new data and the necessary coherence between the gravity field model and the other models in the standards, in particular between the mean pole model and the C21/S21 coefficients of the TVG model; and between the gravity field model and the dealiasing models.

In order to closely follow the actual evolution of the Earth gravity field and to maintain the accuracy of the POD over medium and long time scales, this model has been updated by adding two more years of GRACE measurements until July 2016 and by increasing the TVG maximal degree to 90.

We will discuss the inclusion of the new data and the necessary coherence between the gravity field model and the other models in the standards, in particular between the mean pole model and the C21/S21 coefficients of the TVG model; and between the gravity field model and the dealiasing models.