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ESA's GOCE Satellite Provides Gravity Map of Earth
kaulike writes "The European Space Agency's GOCE satellite, launched in March 2009, has provided a spectacular, highly detailed map of our favorite gravity well. This map shows the normalized surface of the earth as defined by gravity, showing the relative altitude differences from the average for each surveyed point. The article provides the helpful metaphor that a ball resting on this surface would not roll anywhere, even though there would be visual slopes, as gravity is equalized across the globe. There is a fascinating deep area in the Indian ocean (-100M) and a high area near Iceland (+80M), proving conclusively that our world is not homogeneous in terms of density (or practically any other measure). Does anyone know whether these anomalies correspond to known geographic phenomena? Deposits of heavy metals perhaps, or hotspots where the mantle is thinner? I know little about geodetic stuff, but I'm curious about the reasons for wrinkles in the data set."
Gravity map? Heavy, man!
That is all.
No, but they do correspond to the location of the stargates.
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That's a really nice image. Where can I find a 1920x1200 pixel image file of it to use as desktop wallpaper?
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And what well is that? Apparently I'm missing something, and I suspect others the same thing.
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this is quite a very informative article.
my question though from the image produced is that the metres/meters scale shows how "strong" or "weak" the gravity is from the normalized sphere? how is it in the unit of metres/meters? i would appreciate if someone could explain the map more detailed (i probably need another explanation from the article to understand it more.)
the goce satellite is cool. i mean i didn't realize that we have technology such as xenon ion thrusters. i thought they were limited to star trek. my ignorance. :((
thanks in advance. :)
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If you look at the map, a lot of the high-gravity areas tend to appear near highly volcanic areas like the ring of fire (and, as the reader pointed out, Iceland). I wonder if this has something to do with more magma being closer to the surface in those areas...or something similar?
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I'd love to zoom around in google earth to look at this.
Other anomalies include several mobile high gravity areas that seem to track Christiano Ronaldo and several other soccer players.
The U.S. military already has one of these
It's used in inertial navigation for weapons systems. Interestingly, the inertial navigation software itself is available as source code for download, but the data of the map itself is classified to prevent its use by non-U.S. aggressors. Also, for what its worth, the military data resolution is far better than the 100km between data points, as it is with GOCE, but is the resolution falls off on non-projected weapons trajectory route splines.
See also the geoid from the earlier GRACE observations (animated spinning globe) which were 322km resolution, along with a more technical discussion of GOCE:
http://www.scientificblogging.com/planetbye/grace_goce
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ESA must be rolling in money to repeat US experiments. The US experiment repeats its experiment every few months. They detect the gravitation signatures due to mass change like melting/flowing glaciers.
Is it height over/under radar measurement?
Is it height over/under normalised ellipsoid (no terrain)?
If I see a red, does that mean that the satellite saw a stronger or weaker gravitational force at that location?
Looks like R'lyeh lies beneath the Indian ocean...
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Science has become politicized; sure the US already did these experiments but it doesn't guarantee European scientists get timely access. Gathering your own information offers a competitive advantage, whether it's for the prestiege of discovery, industrial value, or the ability to interpret data first to further political goals
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I remember in college physics the prof talked about how oil companies use small deviations in gravity to help identify where large oil deposits might be. Oil is much less dense than rock, so maybe that large well in the Indian ocean is a huge oil deposit?
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Exactly... "the resolution falls off on non-projected weapons trajectory route splines".
You get very good data for the areas in which you want to fly your birds, and lesser data for where you don't expect to do that. This is necessary to, for example, use inertial guidance rather than active TFR in a cruise missile and keep it below the enemy radar.
-- Terry
There is a fascinating deep area in the Indian ocean (-100M) and a high area near Iceland (+80M), proving conclusively that our world is not homogeneous in terms of density (or practically any other measure). Does anyone know whether these anomalies correspond to known geographic phenomena? Deposits of heavy metals perhaps, or hotspots where the mantle is thinner? I know little about geodetic stuff, but I'm curious about the reasons for wrinkles in the data set."
Something that is maybe not so clear from the discussion in TOA, this is an accelerometer mission, and thus reveals a high pass filtering (AKA high-harmonic geoid signatures) of the gravity field. I am not sure if the geoid map in the BBC article is entirely from GOCE data, or if it has other data filling in the low spatial frequencies - it looks pretty similar to older geoid maps.
You might want to read this paper, which points out that
"The interpretation of GOCE geoid and gravity anomaly maps in terms of structure and dynamics of the Earth is
neither simple nor straightforward."
You can see things like typography, sea-mounts (modern gravity data is very good at detecting these), mountain ranges (these are like icebergs, made of lighter material with deep roots, and so are typically actually geoid lows), subduction zones, etc. Since what's going on may be determined by mass / density changes in the deep mantle, figuring out what the observed structures mean can be tough.
However, the scientific interest in these gravity data largely centers around changes in gravity, and many of these are more straightforward. Among the signatures of interest are ocean current changes (might change the dynamic sea level by 10 cm), ice formation and melting (for example, of the Greenland ice sheet), and the global water balance on land (if it rains, it changes the mass loading of the ground, and thus the geoid). Data such as these, and the data from GRACE, are becoming more and more important in the study of global geodynamics. The literally show what's happening on the ground, in basically real time.
GOCE shows slightly stronger gravity in the Himalayas area, but is only a few tens of meters different from the elliptical earth. The mountains are thousands of meters high over a very extended area. I would expect them to show up more strongly. Does this imply that the earth I'd proportionally less dense under those mountains?
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The other application of the Geoid is that it is essentially the "Mean Sea Level" across the globe.
This is essential for you GPS Receiver - the height calculated by a GPS receiver is the height above a theoretical ellipsoid that has pretty much the same shape of the earth. However, the geoid is used to calculate the difference between this "Ellipsoidal Height" and the "height above sea level" that is reported by receivers - sometimes known as "undulation". Without it, Brisbane, Australia would report being about 40m above the water when out on the Bay in a boat.
GPS Receivers typically use a lookup table for it, but can be calculated from scratch using a geoid model such as EGM96 using Spherical Harmonics. Of course, there is an open source implementation of it in C and MATLAB.
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It's worth taking a read of the satellite itself. Apparently, the accelerometers themselves (3 pairs of them) are mounted to within one picometre (that is micro-micro-metre). Gravity measurements are to within 10^-13 G. All pushed ahead by a cool xenon ion engine :)
That's some serious engineering precision. A bit more than your average accelerometer in your iPhone.
There's a bit more on how it works in this article.
Of course, the raw data looks a lots uglier than the beautiful image of the final result, but if the research is for climate change, then manipulating raw data is what they do best ;)
In 2001 (the book) the Monolith was found at the center of a MASCON (mass concentration). I believe the Apollo space program needed maps of the moon's geoid because the moon is "lumpier" and considering the much lower orbits the command/service modules were in (no atmosphere remember) would cause significant deviations in their trajectory.
Yes "lumpier" is an official scientific term.
Think of it another way... The observed 'center' of gravity is always perpendicular to the slope of the geoid.
Thus consider a piece of slope tilted like a forward slash ( / ) The gravity would have to be stronger on the right hand side to hold the ball flat against the slope... Thus the gravity is stronger on the 'high' side, and weaker on the 'low' side.
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If an area has to be higher than the idealized surface to be 'level' (to keep a ball from rolling) won't that be an area that has stronger local gravity?
Interesting... the Indian ocean is nearly 100 meters too shallow.
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Could the "above elevation" spots be useful for reducing the cost of a launch into space? Would that "80m less of gravity" make enough of a difference to be worth building a launch pad on? Hmm, did the calculation (I think) and it seems you'd get a 0.003% reduction in weight. I'm going to guess no?
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wouldn't then the water be more/less dense in places? Would Scuba divers in Iceland be able to go deeper or stay longer? And visa versa for the Indian Ocean?
Are these gravity wells persistent? or are they moving around a little /a lot?
I understand it takes time to map this, but before too much research can be done with this new findings, until they know that these areas are going to stay put, i think some studies may need to keep this in mind.
Curious to see how this relates to ocean flow, I superimposed the ocean currents ontop of this. This was too interesting for me not to post!
:)
Oceans Flow and Gravity Deviations
Note: Sorry that this is a poor edit, but I had to use MS Paint!
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Like others mentioned, GOCE and GRACE use pretty different technology (and are all, at this point, experiments). Also, give Germany some credit - GRACE is a joint US-German experiment. International partnerships are a pretty good way for the US to stretch its earth-observation dollar. See: http://science.nasa.gov/missions/grace/ I don't know much about the GOCE experiment, but GRACE's gravity information has been able to show things like ice cap thinning in Greenland, and the density attributable to large (water) aquifers elsewhere.
and boy did we get it!