26Dec2014

The Potsdam Gravity Potato

Twin-satellites GRACE with the earth’s gravity field (vertically enhanced) calculated from CHAMP data. Credit: GFZ

Twin-satellites GRACE with the earth’s gravity field (vertically enhanced) calculated from CHAMP data. Credit: GFZ

Why do some places on Earth have higher gravity than others?. To help better understand the Earth’s surface, sensitive measurements by the orbiting satellites GRACE and CHAMP were used to create a map.

It is, in effect, a map of Earth’s gravitational field. Since a center for studying these data is in PotsdamGermany, and since the result makes the Earth look somewhat like a potato, the resulting geoid has been referred to as the Potsdam Gravity Potato. High areas on this map, colored red, indicate areas where gravity is slightly stronger than usual, while in blue areas gravity is slightly weaker.

Many bumps and valleys on the Potsdam Gravity Potato can be attributed to surface features, such as the North Mid-Atlantic Ridge and the Himalayan Mountains, but others cannot, and so might relate to unusually high or low sub-surface densities.  Maps like this also help calibrate changes in the Earth’s surface including variable ocean currents and the melting of glaciers. The above map was made in 2005, but more recent and more sensitive gravity maps of Earth were produced in 2011.

Collecting The Data

In total, some 800 million observations went into the computation of the final model which is composed of more than 75,000 parameters representing the global gravitational field. The GOCE satellite alone made 27,000 orbits during its period of service (between March 2009 and November 2013) in order to collect data on the variations in the Earth’s gravitational field.

The final result achieved centimetre accuracy, and can serve as a global reference for sea levels and heights. Beyond the “gravity community,” the research has also piqued the interest of researchers in aerospace engineering, atmospheric sciences, and space debris.

But above all else, it offers scientists a way of imaging the world that is different from, but still complimentary to, approaches based on light, magnetism, and seismic waves. And it could be used for everything from determining the speed of ocean currents from space, monitoring rising sea levels and melting ice sheets, to uncovering hidden features of continental geology and even peeking at the convection force driving plate tectonics. Further Reading: GFZ

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