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The Geoid 2011 model, based on data from LAGEOS, GRACE, GOCE and surface data. Credit: GFZ

The “Potsdam Gravity Potato” Shows Variations in Earth’s Gravity

Article Updated: 23 Dec , 2015

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People tend to think of gravity here on Earth as a uniform and consistent thing. Stand anywhere on the globe, at any time of year, and you’ll feel the same downward pull of a single G. But in fact, Earth’s gravitational field is subject to variations that occur over time. This is due to a combination of factors, such as the uneven distributions of mass in the oceans, continents, and deep interior, as well as climate-related variables like the water balance of continents, and the melting or growing of glaciers.

And now, for the first time ever, these variations have been captured in the image known as the “Potsdam Gravity Potato” –  a visualization of the Earth’s gravity field model produced by the German Research Center for Geophysics’ (GFZ) Helmholtz’s Center in Potsdam, Germany.

And as you can see from the image above, it bears a striking resemblance to a potato. But what is more striking is the fact that through these models, the Earth’s gravitational field is depicted not as a solid body, but as a dynamic surface that varies over time.This new gravity field model (which is designated EIGEN-6C) was made using measurements obtained from the LAGEOS, GRACE, and GOCE satellites, as well as ground-based gravity measurements and data from the satellite altimetry.

The Geoid 2005 model, which was based on data of two satellites (CHAMP and GRACE) plus surface data. Credit: GFZ

The 2005 model, which was based on data from the CHAMP and GRACE satellites and surface data, was less refined than the latest one. Credit: GFZ

Compared to the previous model obtained in 2005 (shown above), EIGEN-6C has a fourfold increase in spatial resolution.

“Of particular importance is the inclusion of measurements from the satellite GOCE, from which the GFZ did its own calculation of the gravitational field,” says Dr. Christoph Foerste who directs the gravity field work group at GFZ along with Dr. Frank Flechtner.

The ESA mission GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) was launched in mid-March 2009 and has since been measuring the Earth’s gravitational field using satellite gradiometry – the study and measurement of variations in the acceleration due to gravity.

“This allows the measurement of gravity in inaccessible regions with unprecedented accuracy, for example in Central Africa and the Himalayas,” said Dr. Flechtner. In addition, the GOCE satellites offers advantages when it comes to measuring the oceans.

Within the many open spaces that lie under the sea, the Earth’s gravity field shows variations. GOCE is able to better map these, as well as deviations in the ocean’s surface – a factor known as “dynamic ocean topography” – which is a result of Earth’s gravity affecting the ocean’s surface equilibrium.

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

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

Long-term measurement data from the GFZ’s twin-satellite mission GRACE (Gravity Recovery And Climate Experiment) were also included in the model. By monitoring climate-based variables like the melting of large glaciers in the polar regions and the amount of seasonal water stored in large river systems, GRACE was able to determine the influence of large-scale temporal changes on the gravitational field.

Given the temporal nature of climate-related processes – not to mention the role played by Climate Change – ongoing missions are needed to see how they effect our planet long-term. Especially since the GRACE mission is scheduled to end in 2015.

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 centimeter 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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Sort by:   newest | oldest | most voted
Steve Nerlich
Member
November 29, 2014 5:27 PM

Anyone know why there’s a big lump near the Philippines? Looks to be mostly ocean.

Aqua4U
Member
November 30, 2014 4:07 PM

Good question. Perhaps a thinner crust is the culprit?

UFOsMOTHER
Member
UFOsMOTHER
November 29, 2014 5:56 PM

Yes and Britain and Europe are in the red but India is in the blue.

postman1
Member
postman1
November 29, 2014 8:06 PM

Why not also post a view of the Western Hemisphere? I’m sure a majority of your readers would like to see the other side of the planet as well and it would make the article more interesting.

Gozlemci
Member
November 30, 2014 12:47 AM

Interesting results…
It would be better to explain the meaning of shape defermations and color changes, more…
And, a question: Do more gravitational feeling cause more tension or happiness ? Where should we go to settle…?

Fernando from Brazil
Member
Fernando from Brazil
November 30, 2014 2:37 AM

Taking a cue from Postman1, why not put a rotating Potsdam Gravity Potato, which can be slowed and repositioned so any portion of the world can be watched? Further on, it would be nice if it’s full screen size, or even zoomable!

Try to get it for us, Matt Williams!

Jeffrey Boerst
Member
November 30, 2014 5:20 AM

Awesome article; awesome graphic! I for one am satisfied thoroughly! wink

tonybudz
Member
tonybudz
November 30, 2014 8:07 AM

The graphics appear a photograph of the world without water then solarized with Gimp or something. I believe the blue indicates lowest and red highest land mass. http://search.yahoo.com/search?p=earth+without+ocean+image&ei=UTF-8&fr=chrf-yff28

NathanialBB
Member
postman1
Member
postman1
November 30, 2014 10:32 AM

Thanks, NathanialBB, that is pretty darn awesome.

skyfan
Member
skyfan
December 2, 2014 11:12 AM

Wow, what an article…
So much about the research and never explained anything about the meaning of the potato image. What are the colors? The heights? Why do the continents don’t show any color? Give us scales! Ok, not so important, but it looks pretty. If you give this image as the main result of the research, I want to understand the Image!

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