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

Wednesday, December 3, 2014

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

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

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

The Earth’s gravitational model (aka the “Potsdam Potato”) is based on data from the LAGEOS, GRACE, and GOCE satellites and surface data. Credit: GFZ

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

About Matt Williams

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The National Aeronautics and Space Administration (NASA) is the United States government agency responsible for the civilian space program as well as aeronautics and aerospace research. President Dwight D. Eisenhower established the National Aeronautics and Space Administration (NASA) in 1958 with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29, 1958, disestablishing NASA's predecessor, the National Advisory Committee for Aeronautics (NACA). The new agency became operational on October 1, 1958.

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The Oxford English Dictionary defines a UFO as "An unidentified flying object; a 'flying saucer'." The first published book to use the word was authored by Donald E. Keyhoe. The acronym "UFO" was coined by Captain Edward J. Ruppelt, who headed Project Blue Book, then the USAF's official investigation of UFOs. He wrote, "Obviously the term 'flying saucer' is misleading when applied to objects of every conceivable shape and performance. For this reason the military prefers the more general, if less colorful, name: unidentified flying objects. UFO (pronounced Yoo-foe) for short." Other phrases that were used officially and that predate the UFO acronym include "flying flapjack", "flying disc", "unexplained flying discs", "unidentifiable object", and "flying saucer". The phrase "flying saucer" had gained widespread attention after the summer of 1947. On June 24, a civilian pilot named Kenneth Arnold reported seeing nine objects flying in formation near Mount Rainier. Arnold timed the sighting and estimated the speed of discs to be over 1,200 mph (1,931 km/h). At the time, he described the objects' shape as being somewhat disc-like or saucer-like, leading to newspaper accounts of "flying saucers" and "flying discs". In popular usage the term UFO came to be used to refer to claims of alien spacecraft. and because of the public and media ridicule associated with the topic, some investigators prefer to use such terms as unidentified aerial phenomenon (or UAP) or anomalous phenomena, as in the title of the National Aviation Reporting Center on Anomalous Phenomena (NARCAP).

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UFO - Unidentified Flying Object An unidentified flying object, or UFO, in its most general definition, is any apparent anomaly in the sky that is not identifiable as a known object or phenomenon. Culturally, UFOs are associated with claims of visitation by extraterrestrial life or government-related conspiracy theories, and have become popular subjects in fiction. While UFOs are often later identified, sometimes identification may not be possible owing to the usually low quality of evidence related to UFO sightings (generally anecdotal evidence and eyewitness accounts). Stories of fantastical celestial apparitions have been told since antiquity, but the term "UFO" (or "UFOB") was officially created in 1953 by the United States Air Force (USAF) to serve as a catch-all for all such reports. In its initial definition, the USAF stated that a "UFOB" was "any airborne object which by performance, aerodynamic characteristics, or unusual features, does not conform to any presently known aircraft or missile type, or which cannot be positively identified as a familiar object." Accordingly, the term was initially restricted to that fraction of cases which remained unidentified after investigation, as the USAF was interested in potential national security reasons and/or "technical aspects" (see Air Force Regulation 200-2). During the late 1940s and through the 1950s, UFOs were often referred to popularly as "flying saucers" or "flying discs". The term UFO became more widespread during the 1950s, at first in technical literature, but later in popular use. UFOs garnered considerable interest during the Cold War, an era associated with a heightened concern for national security. Various studies have concluded that the phenomenon does not represent a threat to national security nor does it contain anything worthy of scientific pursuit (e.g., 1951 Flying Saucer Working Party, 1953 CIA Robertson Panel, USAF Project Blue Book, Condon Committee).

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Photos of Nature | Nature Photography What is The Universe

Wednesday, December 3, 2014