# EIGEN-GRGS.RL03.MEAN-FIELD: new mean gravity field model for altimetric satellite orbit computation

**CoAuthors**

**Event: **2014 Ocean Surface Topography Science Team Meeting

**Session: **Precision Orbit Determination

**Presentation type: **Type Oral

We present a new mean gravity field model for the computation of altimetric satellites orbits, EIGEN-GRGS.RL03.MEAN-FIELD.

The time-variable part of this mean field extends to degree and order 80, based on the recent reiteration of the computation of the GRACE time series of solutions performed at CNES/GRGS, named "Release 03".

EIGEN-GRGS.RL03.MEAN-FIELD is complete to degree and order 260.

It is based on EIGEN-6S2 for the part between degree 81 and 260.

The time-variable gravity (TVG) coefficients between degrees 1 and 80 are obtained from a regression on the GRGS-RL03-v1 monthly time series (2003-2012). For degree 2 this TVG part is extended to 1985-2012 through the use of a GRGS SLR-only (Lageos+Lageos-2) solution between 1985 and 2003.

Outside of the measurements period (1985-2012 for degree 2, 2003-2012 for degrees 3 to 80), the gravity field is extrapolated with a zero-slope assumption.

The modeling of the TVG part includes, as was the case for EIGEN-6S2:

- Two annual and two semi-annual coefficients

- One bias and one drift for each year.

The bias and drift are in general coherent so that the result is a piece wise linear function, except in the case of earthquakes. Three major earthquakes have been introduced in the modelling: Sumatra on 2004/12/26, Concepcion on 2010/02/27 and Sendai on 2011/03/11.

We will present the standards used for the computation, the characteristics of this new mean field and some evaluations in terms of orbit accuracy performance.

The time-variable part of this mean field extends to degree and order 80, based on the recent reiteration of the computation of the GRACE time series of solutions performed at CNES/GRGS, named "Release 03".

EIGEN-GRGS.RL03.MEAN-FIELD is complete to degree and order 260.

It is based on EIGEN-6S2 for the part between degree 81 and 260.

The time-variable gravity (TVG) coefficients between degrees 1 and 80 are obtained from a regression on the GRGS-RL03-v1 monthly time series (2003-2012). For degree 2 this TVG part is extended to 1985-2012 through the use of a GRGS SLR-only (Lageos+Lageos-2) solution between 1985 and 2003.

Outside of the measurements period (1985-2012 for degree 2, 2003-2012 for degrees 3 to 80), the gravity field is extrapolated with a zero-slope assumption.

The modeling of the TVG part includes, as was the case for EIGEN-6S2:

- Two annual and two semi-annual coefficients

- One bias and one drift for each year.

The bias and drift are in general coherent so that the result is a piece wise linear function, except in the case of earthquakes. Three major earthquakes have been introduced in the modelling: Sumatra on 2004/12/26, Concepcion on 2010/02/27 and Sendai on 2011/03/11.

We will present the standards used for the computation, the characteristics of this new mean field and some evaluations in terms of orbit accuracy performance.