The Earth explorer satellite GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) was the first satellite mission within the framework of the Living Planet Program of ESA. This satellite mission was mapping the Earth's gravity field on global scales with a spatial resolution of approx. 100 km which is considerably more precise than all previous and current gravity satellite missions to date.

In this context, one of the most important scientific goals of the GOCE mission was the study of global ocean currents. Ocean currents cause deviations of the sea-level from its equilibrium state with respect to the Earth’s gravity field. These deviations, which are commonly known as ocean topography can amount up to two metres in height. Conclusions on the ocean circulation in association with climate changes can be drawn from knowledge on the ocean topography.

Further scientific objectives of the GOCE Mission were the determination of the structure of the Earth’s crust and the mantel convection as well as the generation of a unique precise global height reference system, which is essential for the precise monitoring of the sea-level and the understanding of its changes.

The key sensor for the gravity measurement on the GOCE satellite was a gravity gradiometer, which was flown there for the first time onboard a satellite. In order to achieve the required high measuring-precision, GOCE orbited the earth at a very low altitude of approx. 250 km. Therefore, the satellite was equipped with an Ion propulsion engine as a so-called Drag Free Control System, which compensates the non-gravitational forces on the satellite and allows practically for flight in a pure free fall around the earth. Furthermore, GOCE was equipped for the first time with a scientific GNSS-receiver made in Europe, which was used to determine the orbit position with Centimetre-accuracy.

The GFZ looks back on many years of experience in analysis of satellite-based gravity field measurements and was therefore a co-operation partner in the ‘GOCE High Level Processing Facility (GOCE-HPF)’ project. The GOCE-HPF project partners processed the GOCE measurement data on behalf of ESA. The project was managed by the Technical University of Munich. GOCE-HPF consisted of a consortium of scientific institutions from Germany, France, Denmark, Italy, Austria, Switzerland and the Netherlands.

Within GOCE-HPF, the GFZ calculated GOCE gravity field models on behalf of ESA using the so-called Direct Aproach. By 2019, six releases of such GOCE gravity field models had been published by ESA. These models are freely downloadable from the GFZ on the website of the International Centre for Global Earth Models (ICGEM).

The GFZ has a long tradition of generating high-resolution Earth gravity field models from the combination of satellite data with terrestrial gravity measurements. The calculation of such models is routinely carried out in close co-operation with the French Groupe de Recherche de Geodesie Spatiale (Toulouse) as part of the EIGEN gravity field processing (EIGEN = European Improved Gravity model of the Earth by New techniques). GFZ and GRGS publish a series of combined global gravity field models containing GOCE measurement data. The most recent model, EIGEN-6C4 (Förste et al. 2014), consists of a data set of spherical harmonic coefficients up to degree and order 2190, which corresponds to a spatial resolution of approx. 10 km. EIGEN-6C4 can be downloaded from the GFZ on the ICGEM website.

Project Partners:

• Technical University Munich, Germany
• University Bonn, Germany
• Danish Technical University Kopenhagen, Denmark
• University Bern, Switzerland
• Centre national d’études spatiales (CNES), Toulouse, France
• Politecnico di Milano, Italy
• Delft University of Technology, The Netherlands
• SRON Netherlands Institute for Space Research, Utrecht, The Netherlands
• Graz University of Technology, Austria

 Project Duration:

• 2004 – 2019

Funding:

• European Space Agency ESA

Project related Data Publications:

• Förste, Christoph; Abrykosov, Oleh; Bruinsma, Sean; Dahle, Christoph; König, Rolf; Lemoine, Jean-Michel (2019): ESA’s Release 6 GOCE gravity field model by means of the direct approach based on improved filtering of the reprocessed gradients of the entire mission (GO_CONS_GCF_2_DIR_R6). GFZ Data Services. https://doi.org/10.5880/ICGEM.2019.004
• Förste, Christoph; Bruinsma, Sean.L.; Abrykosov, Oleh; Lemoine, Jean-Michel; Marty, Jean Charles; Flechtner, Frank; Balmino, Georges; Barthelmes, Franz; Biancale, Richard (2014): EIGEN-6C4 The latest combined global gravity field model including GOCE data up to degree and order 2190 of GFZ Potsdam and GRGS Toulouse. GFZ Data Services.
  https://doi.org/10.5880/icgem.2015.data