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ESA releases the fourth generation GOCE gravity field solutions

20 March 2013

The fourth generation GOCE gravity field solutions based on the so-called Time-wise (TIM) and Direct (DIR) methodologies, have been processed and verified by the GOCE HPF team, and are now made available to the public by ESA.

This is a major milestone for the GOCE mission, after the release of the previous third generation gravity solutions on 7 November 2011.

While the third generation spanned 18 months-worth of data, these fourth generation solutions span almost three years of Mission data, from November 2009 up to July 2012, boosting the effective data volume used from 12 months up to 27.

The coefficients for both TIM and DIR models can be downloaded directly from the links below, together with the associated data sheets discussing the model characteristics and more specific features of the resulting gravity fields. The full EGM_GOC_2 product shall shortly be made available through the GOCE Virtual Online Archive.

Further information on the released data sets:

Data Period:

  • TIM: 01/11/2009 – 19/06/2012. Effective data volume: approx. 26.5 months
  • DIR: 01/11/2009 – 01/08/2012 Effective data volume: 13430 orbital revolutions ~ 837 days

Key Characteristics:

TIM

  • TIM is a GOCE-only solution in a rigorous sense. No external gravity field information is used (neither as reference model, nor for constraining the solution)
  • SST processing changed from energy integral approach (releases 1 to 3) to short-arc integral method
  • SGG processing strategy is unchanged for all 4 releases of time-wise models
  • Related variance-covariance information represents the true errors of the coefficients
  • Solution can be used for independent comparison and combination on a normal equation level with other satellite-only models (e.g. GRACE), terrestrial gravity data, and altimetry
  • Since in the low degrees the solution is based solely on kinematic GOCE orbits, it is not competitive with a GRACE model

DIR

  • DIR is a satellite-only model based on a full combination of GOCE-SGG with GRACE and LAGEOS, leading to an excellent performance of the long as well as of the short wavelengths
  • More processing details are presented in Bruinsma et al. 2010 and Pail et al. 2011

GOCE Input Data for the two solutions:

TIM

  • SST_PKI: Kinematic GOCE orbits
  • SST_PCV: Covariance Information related to kinematic orbits
  • Gradiometer data:
  • EGG_NOM: Level 2 gravity gradients in Gradiometer Reference Frame (GRF)
  • Rotations between inertial and gradiometer frame
  • EGG_CCD: common mode accelerations in GRF

DIR

  • SST_PKI: Kinematic GOCE orbits as positions for the gradiometry observation equations
  • SST_PRM: Rotations between inertial and Earth-fixed reference frames
  • EGG_NOM: Level 2 gravity gradients in GRF
  • EGG_IAQ: Rotations between inertial and gradiometer reference frames
  • Rotations between inertial and gradiometer frame
  • Other satellite data:
    • LAGEOS-1/2 SLR data (measurement period 1985 – 2010) and GRACE GPS-SST & K-band range-rate data (measurement period February 2003 – January 2011), both from the GRGS RL02 GRACE processing (Bruinsma et al. 2009)
    • GRACE GPS-SST & K-band range-rate data (measurement period October 2003 – September 2012) from the GFZ RL05 GRACE processing (Dahle et al. 2012)

Download the fourth generation Time-wise solution and Data Sheet

Download the fourth generation Direct solution and Data Sheet