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schadeaux

Gravity Anomalies!

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user posted image

Grace globe - Gravity highs are marked red;

gravity lows are blue. (Grace)

University of Texas Press Release

July 21, 2003 - The joint NASA-German Aerospace Center Gravity Recovery and Climate Experiment (Grace) mission has released its first science product, the most accurate map yet of Earth's gravity field. Grace is the newest tool for scientists working to unlock secrets of ocean circulation and its effects on climate.

Created from 111 days of selected Grace data, to help calibrate and validate the mission's instruments, this preliminary model improves knowledge of the gravity field so much it is being released to oceanographers now, months in advance of the scheduled start of routine Grace science operations. The data are expected to significantly improve our ability to understand ocean circulation, which strongly influences weather and climate.

Dr. Byron Tapley, Grace principal investigator at UT's Center for Space Research, called the new model a feast for oceanographers. "This initial model represents a major advancement in our knowledge of Earth's gravity field. "Pre- Grace models contained such large errors many important features were obscured.

Grace brings the true state of the oceans into much sharper focus, so we can better see ocean phenomena that have a strong impact on atmospheric weather patterns, fisheries and global climate change."

Grace is accomplishing that goal by providing a more precise definition of Earth's geoid, an imaginary surface defined only by Earth's gravity field, upon which Earth's ocean surfaces would lie if not disturbed by other forces such as ocean currents, winds and tides.

The geoid height varies around the world by up to 200 meters (650 feet).

"I like to think of the geoid as science's equivalent of a carpenter's level, it tells us where horizontal is," Tapley said. "Grace will tell us the geoid with centimeter-level precision."

So why is knowing the geoid height so important? JPL's Dr. Lee-Lueng Fu, scientist on Topex/Poseidon and Jason project said, "The ocean's surface, while appearing flat, is actually covered with hills and valleys caused by currents, winds and tides, and also by variations in Earth's gravity field. "Scientists want to separate out these gravitational effects, so they can improve the accuracy of satellite altimeters like Jason and Topex/Poseidon, which measure sea surface height, ocean heat storage and global ocean circulation. This will give us a better understanding of ocean circulation and how it affects climate."

Dr. Michael Watkins, Grace project scientist at JPL, put improvements to Earth's gravity model into perspective. "Scientists have studied Earth's gravity for more than 30 years, using both satellite and ground measurements that were of uneven quality. "Using just a few months of our globally uniform quality Grace data, we've already improved the accuracy of Earth's gravity model by a factor of between 10 and nearly 100, depending on the size of the gravity feature. In some locations, errors in geoid height based upon previous data were as much as 1 meter (3.3 feet). Now, we can reduce these errors to a centimeter (0.4 inches) in some instances. That's progress."

Dr. Christoph Reigber, Grace co-principal investigator at GeoForschungsZentrum Potsdam, said, "As we continue to assess and refine Grace's instruments and subsystems, we're confident future monthly gravity solutions will be even better than the map we're releasing now. "Those solutions will allow us to investigate processes associated with slow redistribution of mass inside Earth and on its land, ocean and ice surfaces. Our initial attempts to identify such small gravity signals with Grace look very promising."

Grace senses minute variations in gravitational pull from local changes in Earth's mass by precisely measuring, to a tenth of the width of a human hair, changes in the separation of two identical spacecraft following the same orbit approximately 220 kilometers (137 miles) apart. Grace will map the variations from month to month, following changes imposed by the seasons, weather patterns and short-term climate change.

Grace is a joint partnership between NASA and the German Aerospace Center. The UT Center for Space Research has overall mission responsibility. GeoForschungsZentrum Potsdam is responsible for German mission elements. Science data processing, distribution, archiving and product verification are managed under a cooperative arrangement between JPL, UT, and GeoForschungsZentrum Potsdam.

For more information, visit: http://www.csr.utexas.edu/grace or http://www.gfz-potsdam.de/grace

Model images are at: http://photojournal.jpl.nasa.gov/catalog/PIA04652 and http://www.csr.utexas.edu/grace ; and http://www.gfz-potsdam.de/grace

eXoNews

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It's interesting how the good ol' Bermuda triangle seems to be located in a low gravity area.

Could it be possible that...?

Nah.

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It's interesting how the good ol' Bermuda triangle seems to be located in a low gravity area.

Could it be possible that...?

Nah!!! We did that a couple of weeks ago and strangely I think The Bermuda Triangle was in a higher gravity zone then .

What I find really interesting exeter, is the fact that gravity isn't constant . For instance if you where to be standing in Florida you would weigh less than if you were in the Gulf of Mexico (geography is not my strong point and I will allow room for a state or small country margin of error) . Also gravity is affected by the heavenly bodies in our Universe. Mars right now appears to be affecting the tides and the Moons pull is well documented in having an affect on our gravity .

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Kismit, if you look at the grace globe you'll notice that the Rocky Mountains are located in a higher gravity zone. I live very close to the Rockies.

Theoretically, if I moved to the Midwest, I could maintain my steady diet of beer and pizza and still lose weight.

Woo hoo!!! w00t.gif

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The identification of gravity anomalies has had a major impact in surveying. The big regional gravity anomalies have been accommodated to some degree for many decades, but the failure to identify "local" gravity anomalies has brought into doubt the accuracy of many so-called precision surveys. It is now known that "deviations of the vertical" and the direction of the gravity vector can cause systematic errors that are well in excess of the surveying instruments precision, thus effectively negating the stated accuracy of surveyed values.

The term "deviation of the vertical" means that a surveying instruments plumb point is not truly vertical. To see how the gravity vector magnitude and direction changes in a country like Switzerland, view the following URL and click on the map.

http://www.ggl.baug.ethz.ch/research/wg18/

If you are interested in a good primer on gravity surveying and the things that effect the gravity vector magnitude and direction go to the following URL:

http://www.sfu.ca/earth-sciences/courses/n...y/3-Gravity.htm

The new laser surveying instruments allow measurement precisions unattainable several decades ago, but if they do not include gravity surveys at the benchmarks the accuracy can be questionable.

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It's interesting how the good ol' Bermuda triangle seems to be located in a low gravity area.

Could it be possible that...?

Nah.

I would like to see the images of the area known as the Devil's Sea could they look similar to the Bermuda Triangle image?

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Hey, Exeter? What state do you live in? Cause im in da red zone too! w00t.gif (I live in Washington State!)

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I remember reading about how they initially came upon gravitational anomalies on Earth - one of the shuttles in orbit would actually slow just the tiniest fraction in its orbit when it passed over one of these anomalies. There's similar ones like it on the Moon, called MasCons (Massive Concentrations of matter). They're basically huge clumps of really, really dense moon-stuff scattered all over the lunar globe.

Quick lesson for those who care: whenever you change your distance from the center of the Earth, the power of gravity acting on you changes. It makes sense when you think about it. Gravity, like light, gets weaker over distance. So when you go from the plains of Saskatchewan to the peaks of the Rocky Mountains, you're getting farther from the center of the Earth, and weakening the affect of gravity on you by a barely perceptible amount.

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The mascons on the moon present very intense gravity anomalies and disturbed the orbits of the various moon orbiters. This from a JPL site:

"The Moon shows many areas of excess subsurface mass (mascons) that cause the gravity field of the Moon to be very "lumpy," requiring constant adjustments for orbiting spacecraft."

"The mascons are always found beneath the floors of large impact basins and probably represent plugs of dense, uplifted rocks from the lunar mantle."

http://www.lpi.usra.edu/expmoon/3minmoon.html

The Russians had considerable interest in mascons, putting several of their landers in the Mare Crisium and actually returning lunar samples from there. I suspect the Russians had a different theory on the source of the mascons than JPL.

http://www.astrosurf.com/lunascan/luna_24.htm

The last U.S. lunar orbiter did not carry a camera even though the available technology could have given researchers high resolution pictures of the illuminated surface, equal or better than those from the Apollo's in orbit.

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