June 29, 2010

GOCE Gravity Model Released

Europe's GOCE satellite has produced one of the most unique views of the Earth that we have ever seen.

The colorful new map produced by the satellite depicts the influence the pull of gravity has around the world.

Known as a geoid -- a mathematical figure of the Earth through gravitational calculations -- it essentially defines where the level surface is on our planet. It shows us which way is "up" and which way is "down".

The GOCE satellite flies so low in orbit that it comes very close to falling out of the sky. But that low path is needed for it to make such delicate measurements.

Scientists say the data produced from the satellite will serve many applications.

The geoid could be very beneficial to climate studies by helping researchers understand how the great mass of ocean water is moving heat around the world.

The new map was presented at a special Earth observation (EO) symposium in Norway.

The symposium is dedicated to data collected from satellites through the European Space Agency (ESA) and other agencies. Europe is the midst of a huge program of EO development which plans to launch some 20 missions before the end of the decade. The Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) satellite is the first of the armada of scientific and environmental monitoring spacecraft.

The GOCE satellite, launched in 2009, flies pole to pole at an altitude of only 153 miles -- the lowest orbit of any research satellite in operation today.

GOCE carries three pairs of precision-tuned platinum blocks inside its gradiometer instrument that sense accelerations which are as small as 1 part in 10,000,000,000,000 of the gravity experienced on Earth. This has allowed it to map the almost imperceptible differences in the pull exerted by the mass of the planet from one place to the next.

The geoid has been formed through two months of observations by GOCE. "I think everyone knows what a level is in relation to construction work, and a geoid is nothing but a level that extends over the entire Earth," explained the Technical University of Munich's Professor Reiner Rummel, the chairman of the GOCE scientific consortium.

"So with the geoid, I can take two arbitrary points on the globe and decide which one is 'up' and which one is 'down'," Rummel told BBC News.

The geoid is of great interest to oceanographers because it is the shape the world's seas would adopt if there were no tides, no winds and no currents.

If researchers were then to subtract the geoid from the actual observed behavior of the oceans, the scale of these other influences becomes apparent.

This information is very crucial to climate modelers who try to represent the way oceans manage the transfer of energy around the world.

The geoid is important in other technical areas as well.

For example, in construction it would tell engineers which way a fluid would naturally want to flow through a pipeline.

It is important to geophysicists who will want to use GOCE data to try to probe what is happening deep inside the Earth, especially in places that are prone to earthquakes and volcanic eruptions.

"The GOCE data is showing up new information in the Himalayas, central Africa, and the Andes, and in Antarctica," explained Dr Rune Floberghagen, ESA's GOCE mission manager.

"This is, in one sense, not so surprising. These are places that are fairly inaccessible. It is not easy to measure high frequency variations in the gravity field in Antarctica with an airplane because there are so few airfields from which to operate," he said.

The extremely low orbit of GOCE was expected to limit its mission to only a few years, but ESA now thinks it may be able to continue flying the satellite until 2014.

Unusually quiet solar activity has produced calm atmospheric conditions, meaning GOCE has used far less fuel to maintain its orbit. Once the fuel runs dry the satellite will slow in the low orbit and eventually fall from the sky.


Image 2: The first global gravity model based on GOCE satellite data has been presented at ESA's Living Planet Symposium. Based on only two months of data, from November and December 2009, it illustrates the excellent capability of GOCE to map tiny variations in Earth's gravity field. Credits: GOCE High Level Processing Facility


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