Accueil / Données scientifiques / Champ de gravité / Modèles variables GRACE/LAGEOS / Static field

Static field

Static gravity field models

Release 01: EIGEN-GL04S, EIGEN-GL04C, EIGEN-GL04C-ANNUAL
Release 02: EIGEN-GRGS_RL02_MEAN-FIELD

Introduction to static coefficients and time-variable terms

For many applications, particularly precise orbit computation, a static gravity field is not sufficient. The main features of the time variations of the gravity field are annual and semi-annual signals and, to a lesser extent, secular drifts. This is why some of our static fields propose a series of periodic and secular gravity variations for the first degrees of the gravity field (up to degree 50). Those variations include annual, semi-annual and drift terms, based on the GRACE time-variable solutions. In the case of EIGEN-GRGS.RL02.MEAN-FIELD, we also provide a “pre-Sumatra” correction term, which needs to be added if one works before December 24, 2004.

Formats

Release 01

EIGEN-GL04S

EIGEN-GL04S is a strictly static gravity field model, up to degree and order 150 from GRACE and LAGEOS data only. It is given in normalized spherical harmonic (SH) coefficients in ITRF2000, and uses exactly 2 years of GRACE + LAGEOS data (73 10-day periods between 2003/02/24 and 2005/02/23). Its reference date is 2004.0. This field does not include time-variable terms (see EIGEN-GL04S-ANNUAL below).

EIGEN-GL04C

EIGEN-GL04C is a strictly static gravity field model, up to degree and order 360, from GRACE and LAGEOS data,plus surface data (Earth altimetric and gravimetric data). Its reference date is 2004.0.

EIGEN-GL04S-ANNUAL

EIGEN-GL04S-ANNUAL is based on EIGEN-GL04S, this field includes time-variable components: drift, annual and semi-annual sine and cosine.Drift terms however should be taken with some care since they were determined over only two years.

Release 02

EIGEN-GRGS.RL02-MEAN-FIELD

EIGEN-GRGS.RL02.MEAN-FIELD is a static gravity field model, up to degree and order 160, based on 4.5 years of GRACE and LAGEOS data (March 2003 to September 2007). It includes time-variable terms up to degree and order 50.

  • Reference epoch is 2005.00;
  • Tide convention is "tide free";
  • The field is complete to degree and order 160;
  • Up to degree and order 50, are present...
    • drifts with the acronym "DOT",
    • annual sine and cosine terms with the acronym "S1A" and "C1A",
    • semi-annual sine and cosine terms with the acronym "S2A" and "C2A",
    • an offset, with the acronym "SUM", to take into account the permanent deformation of the gravity field associated with the December 2004 Sumatra earthquake. The principle of this correction is that if one works BEFORE December 24, 2004, one has to ADD this correction to the static gravity field; if one works AFTER this date, one has to IGNORE this correction. This means that EIGEN-GRGS.RL02.MEAN-FIELD is a "post-Sumatra" mean gravity field and that the Sumatra correction has only to be added if one works before the earthquake date of occurrence.

EIGEN-GRGS.RL02-MEAN-FIELD.static_part.dg_050

We also provide the static-only part of EIGEN-GRGS.RL02.MEAN-FIELD, limited to maximum degree and order 50, under the name EIGEN-GRGS.RL02.MEAN-FIELD.static_part.dg_050. This is the same as the above-described model, but all time-dependant terms and all terms of spherical harmonic degree greater than 50 have been removed. To see the full temporal gravity variations, the 10-day solutions must be compared to this model (i.e. by subtracting this reference from the 10-day solutions).

EIGEN-GRGS.RL02-MEAN-FIELD.static_part.dg_050 grids

In addition, we provide grids in geoid heights and equivalent water heights, with the following characteristics:

  • Tides: “tide free”
  • Degrees included: 02 to 50
  • Parameters of the ellipsoid:
    • a= 0.63781364600000E+07
    • 1/f= 0.29825765000000E+03
    • GM= 0.39860044150000E+15