GRACE SOLUTIONS
6 years of gravity variations from GRACE and LAGEOS data from CNES/GRGS
R Biancale, J-M Lemoine, G Balmino, S Bruinsma, F Perosanz, J-C Marty (CNES/GRGS, Toulouse, France), S Loyer, S Bourgogne (Noveltis, Toulouse, France), P Gégout (EOST, Strasbourg, France)
Contacts:
Richard.Biancale@cnes.fr
Jean-Michel.Lemoine@cnes.fr
NEWS
Last update: 2009/09/10
10-day gravity fields available until April 2009!
16 new 10-day models are available in release 2 standards, covering November 14th 2008 to April 22nd 2009. Download new products. Correspondance between 1950 Julian dates, calendar dates and Year/Day of Year dates are given in the DATES FORMAT page. See DATES format. In addition, we also provide information about the number of days included in each 10-day model, as well as statistics of the Equivalent Water Heights signal over the oceans.
GRGS gravity fields RELEASE 2
Version 02 of the CNES/GRGS time-variable gravity field models based on the GRACE data is now available under the name "Release 02" or "EIGEN-GRGS.RL02". Here are the main features of this new release:
- Models are provided every 10 days and are based solely on the 10 days (maximum) of data that are in this time interval (whereas "version 1" models were provided every 10 days but were based on three consecutive 10-day periods with the weighting 0.5/1./0.5);
- A new "mean field" has been computed and is delivered together with the RL02 time series. It is based on 4.5 years of GRACE and LAGEOS data (March 2003 to September 2007). This mean gravity field, named EIGEN-GRGS.RL02.MEAN-FIELD, is complete to spherical harmonic degree and order 160. It contains drifts, annual and semi-annual terms up to degree and order 50. It also contains an offset, up to degree and order 50, in order to take into account the December 2004 Sumatra earthquake. A more detailed description of this mean field is given in the static field page ;
- 10-day models are stabilized towards EIGEN-GRGS.RL02.MEAN-FIELD, more precisely towards the realization of EIGEN-GRGS.RL02.MEAN-FIELD at each given epoch, with a new constraint law that depends on the degree and on the order of each coefficient (in version 1, the law was only degree-dependent and the models were constrained towards the static part of EIGEN-GL04S and later EIGEN-GL04C). The RL02 files can be downloaded here ;
SUMMARY
This site contains static gravity fields as well as a series of gravity field models expressed in normalized spherical harmonic coefficients from degree 2 to degree 50.
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).
At this day, two series of variable fields have been released. The first release 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 consists of 10-day models only. In both cases, fields are given every 10 days. The static 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)
The models are tide free.
Gravitational variations such as Earth tides (according to IERS Convention 2003), ocean tides from the FES-2004 model (LEGOS, Observatoire Midi-Pyrénées), ECMWF 3D-atmospheric pressure fields every 6 hours (from P Gégout, EOST) and the MOG2D barotropic ocean model (LEGOS) 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 and ECMWF models.
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 below.
The grids and maps of geoid variations and equivalent water height (EWH) variations at 10-day intervals (mean 1°×1° values ) as well as two movies (in animated-gif format) are also provided.
DOWNLOADABLE PRODUCTS
The following products available on our website:
- Time-variable gravity fields: RELEASE 01 (30-day models given at 10-day intervals)
- Time-variable gravity fields: RELEASE 02 (10-day models)
- Static field
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Visits since October 6th 2008