Big and small dents

The Earth explorer satellite GOCE (Gravity Field and Steady-State Ocean Circulation Explorer), built by the European Space Agency ESA, was successfully launched today at 15:21 GMT from the Russian Cosmodrome Plesetsk. GOCE is the first satellite mission within the framework of the Living Planet Programme of ESA and will map Earth's gravity field in unprecedented detail. From the data obtained, the GFZ - German Research Centre for Geosciences will calculate its own, high resolution gravity field. "The accuracy of the depiction of the Earth's gravity field, well known as the 'Potsdam Gravity Potato' will now be enhanced by orders of magnitude", says Prof. Dr. Hüttl, Scientific Executive Director of the GFZ. The GFZ, which looks back on many years of experience in analysis of satellite-based gravity field, measurements participates in the evaluation of GOCE data as a co-operating partner within the framework of the so called High Level Processing Facility (HPF) under the Project Managment of the Technical University Munich and together with scientific institutions from Germany, France, Denmark, Italy, Austria, Switzerland and the Netherlands.

GOCE will map the Earth's gravity field with a spatial resolution of approx. 100 km which is considerably more precise than all gravity satellite missions to date. One of the most important scientific goals of the GOCE mission will be the study of the global ocean currents. Ocean currents cause deviations of the sea-level from its equilibrium state with respect to the Earth's gravity field. This 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. "By combining GOCE-measurement data with sea-level hights measured by other satellites, it will be possible for the first time to directly measure the ocean topography and its possible changes", explains Dr. Frank Flechtner, who processes gravity field data at GFZ. This will be a new contribution to our knowledge of the ocean and its variation due to climate change.

Further scientific objectives of the GOCE Mission are 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 is a gravity gradiometer, which is now flown for the first time onboard a satellite. In order to achieve the required high measuring-precision, GOCE orbits the earth at a very low altitude of approx. 250 km. Therefore the satellite is 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 is equipped with a scientific GPS-receiver, made in Europe, which will be used for the first time on board a satellite to determine the GOCE orbit position with centimetre-accuracy.

Source: Helmholtz Association of German Research Centres