GRACE > GRGS Time Variable Models from GRACE / LAGEOS > Introduction to GRACE solutions

Groupe de Recherche de Géodésie Spatiale Centre national d’études spatiales

Summary

This site contains time series of gravity field models as well as mean gravity field models, expressed in normalized spherical harmonic coefficients.

These fields are recovered from GRACE GPS and K-band range-rate data and from LAGEOS-1/2 SLR data (LAGEOS data provide over 90% of the information on the coefficient C(2,0) of the gravity field, whereas GRACE data provide nearly 100% of the information on all the other harmonic coefficients).

To this day, three series of variable fields have been released. The first release (standards 2005) consists of 30-day models based on the running average of three 10-day data periods with weights 0.5/1.0/0.5. The second release (standards 2009) consists of strictly 10-day models. In both cases, fields are given every 10 days and are complete up to spherical harmonic degree 50. The third release (standards 2013), based on the reprocessed level-1B data, will feature monthly and 10-day solutions up to spherical harmonic degree 80.

The mean fields used as reference are also given on this website (EIGEN-GL04S/C for release 01 and EIGEN-GRGS.RL02.MEAN-FIELD for release 02, EIGEN-GRGS.RL03-v2.MEAN-FIELD for release 03)

The models are tide free.

Gravitational variations such as Earth tides, ocean tides, 3D-atmospheric pressure fields and barotropic ocean response model have been taken into account in the processing of the data. The time-variable gravity field models therefore only depart from the static gravity field by the unmodelled effects: hydrology, snow cover, baroclinic oceanic signals and post-glacial rebound. The uncertainties of those fields include errors in the measurement data, in the processing, lack of coverage in some instances, and possible remaining errors in the FES, MOG2D/TUGO and ECMWF models.

  RL01 and RL02 RL03
IERS Conventions 2003 2010
Ocean tide model FES2004 (LEGOS) FES2012 (LEGOS)

Atmospheric pressure dealiasing

(processed by P Gégout, CNRS/GET)

ECMWF operational, every 6 h ECMWF ERA-Interim, every 3 h
Ocean barotropic response model MOG2D (LEGOS), every 6h TUGO (LEGOS), every 3 h

It is to mention that a constraint towards the mean field is applied for the higher degree coefficients in order to stabilize them, mainly effective from degree 30 and up. Details are given in the respective releases sections.

The grids and maps of geoid variations and equivalent water height (EWH) variations at 10-day or monthly intervals (mean 1°×1° values), as well as movies (in animated-gif format), are also provided.

Important notice

It is reminded to the users of the GRGS products that NO SMOOTHING OR FILTERING is necessary when using them, since they have already been stabilized during their generation process.

Latest models

See RL03 page for recent information about latest available models.

Release 03

The third release of the CNES/GRGS time-variable gravity field models, based on the reprocessed "V2" version of the GRACE level-1b data, is now available under the name "Release 03" or "RL03".

This release will have different versions depending on the time sampling of the solution. The first version "v1", available today, is a monthly solution. Future versions will feature 10-day solutions.

Description of RL03-v1:

  • Models are provided on a monthly basis;
  • Maximum spherical harmonic degree is 80;
  • The inversion processed is now based on a truncated SVD scheme;
  • In parallel to this monthly solution, a new "mean field" has been computed and is now available under the name "EIGEN-GRGS.RL03.MEAN-FIELD".

THE GRACE PLOTTER : a new website for plotting and comparing GRACE solutions

We propose to the community of GRACE users a new website for plotting and comparing GRACE solutions.

On this website you will be able to plot time series of GRACE solutions in terms of equivalent water height (EWH), either for point locations, spherical rectangles or polygons (up to 10 summits), or hydrological basins (approx. 30 are available, ordered by surface area from the Amazon to the Brahmaputra).

Not only the CNES/GRGS releases are present there, but also the three RL05 releases from CSR, GFZ and JPL, filtered using the DDK5 filter. The series of CSR, GFZ and JPL were obtained from the ICGEM data base.

We hope this website can be a useful tool for most GRACE users whether they want to conduct scientific research, solutions comparisons or evaluation. It is still in a development phase and all suggestions for improvement are welcome.

The location of this new site is: www.thegraceplotter.com.

affiche