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Space Earth

ESA's GOCE Satellite Provides Gravity Map of Earth 119

Posted by Soulskill from the time-to-outsource-your-weight-lifting-to-india dept.
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."
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ESA's GOCE Satellite Provides Gravity Map of Earth More

ESA's GOCE Satellite Provides Gravity Map of Earth

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  • First? (Score:5, Funny)

    by frank_adrian314159 ( 469671 ) on Monday June 28, 2010 @05:34PM (#32723810) Homepage

    Gravity map? Heavy, man!

    • Re: (Score:1, Funny)

      by Anonymous Coward

      There's that word again; "heavy". Why are things so heavy in the future? Is there a problem with the earth's gravitational pull?

    • Re: (Score:2)

      by jlar ( 584848 )

      I was just wondering whether athletes take gravity into account when trying to break World records. The best place to do athletics would then be near the Equator since the gravity is lower there by 0.5% compared with the poles. And that might give a centimeter or so in high jump and more in pole vault or long jump compared with mid-latitudes (potential energy and thus achieved height is a linear function of gravity near the Earth surface, meaning that a 0.5% drop in gravity means a 0.5% increase in height).

  • known geographic phenomena (Score:5, Funny)

    by nurb432 ( 527695 ) on Monday June 28, 2010 @05:36PM (#32723826) Homepage Journal

    No, but they do correspond to the location of the stargates.

    • SHHHHHHH! You're not supposed to tell them yet!

    • Re: (Score:1, Troll)

      by forkazoo ( 138186 )

      No, but they do correspond to the location of the stargates.

      Is "Stargates" a codename for yo momma's orifices? I only ask because, I'm certain she has sufficient mass to distort a gravity map. I feel quite ribald for saying this.

    • 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.

      • Are you sure? I'm fairly sure that I recall the monolith on the moon being called TMA1, standing for Tycho Magnetic Anomaly - it was found as a magnetic anomaly, not as a mass anomaly.

  • Where's a 1920x1200pxl Image? (Score:3, Interesting)

    by Doc Ruby ( 173196 ) on Monday June 28, 2010 @05:36PM (#32723832) Homepage Journal

    That's a really nice image. Where can I find a 1920x1200 pixel image file of it to use as desktop wallpaper?

    • Not the same, but equally cool:

      http://www.google.com/mars/

      • Where's the street view!? We've sent how many rovers there and they haven't even converted 1% of the images for Mars Street view!?

        • Where's the street view!? We've sent how many rovers there and they haven't even converted 1% of the images for Mars Street view!?

          I don't know what you are doing wrong. They provide even greater coverage than on Earth. 100% of all Mars' streets have been mapped.

    • Re: (Score:2)

      by Herve5 ( 879674 )

      GOCE is a mission from theEuropean Space Agency: get the images on an ESA site, not on the BBC:

      http://earth.esa.int/object/index.cfm?fobjectid=7029 [esa.int]

      and more precisely, this specific image is on slide 7 (rescalable ;-) ) of the pdf at http://earth.esa.int/pub/ESA_DOC/GOCE/GOCE%20Science%20Data%20Processing%20System%20Status%20and%20Plans.pdf [esa.int]

      • Actually, I was able to export the SVG of the image from page 9 of that PDF:

        pdf2svg GOCE-Science-Data-Processing-System-Status-and-Plans.pdf page9.svg 9

        Checked it to be sure:
        eog page9.svg

        Then opened it in the gimp:
        gimp page9.svg

        The actual geoid is narrower than the image with its margins. But it's not in WUXGA ratio, either. So I scaled it to 2087xW, keeping aspect ratio, making the geoid 1920 pixels wide, with 70 blank lines below, which I cropped at 1920x1080. Then I copy/pasted more lines in the intensit

  • And what well is that? Apparently I'm missing something, and I suspect others the same thing.

  • cool (Score:5, Interesting)

    by john_uy ( 187459 ) on Monday June 28, 2010 @05:47PM (#32723932)

    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. :)

    • Re:cool (Score:5, Informative)

      by demonbug ( 309515 ) on Monday June 28, 2010 @06:01PM (#32724086) Journal

      The map is showing the deviation from an ideal spheroid that would result in the observed gravity variation. So, positive meters basically means that if the Earth were made of stuff of a uniform density, the surface of the earth would be this many meters above the ideal surface (gravity is weaker here than expected). Conversely, negative meters means gravity is stronger here than expected, and so correlates to a "low" (low elevation being closer to the center of mass of the earth, meaning stronger gravity).

      The map is essentially showing what the surface of the earth would look like if all variation in gravity (what they observed) was due to variation in the shape of the earth, rather than density. At least, I think that is what they are showing - I don't think the article actually states if this is raw data or if it has been processed (to apply a free-air correction, for example, which would remove variability due to the actual variations in elevation of the earth's surface).

      Make sense? It isn't as complicated as my half-assed explanation might make it seem (well, it is complicated, but the concept is simple).

        • Re: (Score:3, Informative)

          by maeka ( 518272 )

          No, because that image shows one how height above the ellipsoid (not spheroid as someone said above) model of the earth (as used in GPS / etc.) minus the geoid model deviation (what these satellites are, in effect, measuring) equals your orthometric height (what most people call "elevation").

          I don't believe this helps the GP's query, because it doesn't explain what the geoid model is.

          What most people never think about is that old-school surveying (with a conventional level) always, even before we understood

      • Re: (Score:2)

        by john_uy ( 187459 )

        thanks. got it. :)

      • Re: (Score:2)

        by tyldis ( 712367 )

        TFA reports the data has been collected over two months which should give several repeated measurements over the same area and thus compensate for most variable things.
        That noted, the project has been receiving science data from the gradiometer (known as the EGG) for about a year now with inly minor interruptions.

        The GOCE is a spectacular satellite, as it's low 250km orbit means it actually suffers from drag. Hence the Xenon Ion Thruster which keeps it from falling down. Normally a satellite does not have t

      • uhm, no. the geoid is at negative height where the gravity is WEAKER. The geoid consists of a surface where a ball would never roll because the gravity differential would counteract the slope (or vice-versa)...

        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 gravit

      • 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.

    • 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?

      That is my understanding, based on the explanation and informative diagram at the bottom of the article. :)

    • I'm no expert, but it looks like they calculated an isosurface (a surface where every point has the same perpendicular gravitational pull) and colored their map based on the difference in height between this isosurface and the surface of the normalized sphere. On a normalized sphere (e.g. at sea level) gravity would be stronger where the isosurface is higher and weaker where the isosurface is lower.

  • Interesting Pattern Near the Ring of Fire (Score:5, Interesting)

    by BJ_Covert_Action ( 1499847 ) on Monday June 28, 2010 @05:55PM (#32724012) Homepage Journal
    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?
    • Perhaps it is due to the effect of having two tectonic plates in close proximity to each other. For instance, in the immediate vicinity of a subduction zone the satellite would essentially see two stacked tectonic plates, which could account for the differences in observed density.
      Anybody with more than a freshman-level understanding of geology want to correct me?

      • Except that the two plates from which Iceland has formed (American and Eurasian?) are moving away from each other instead of moving together and one overlapping the other. Besides, if this were the case the "density" would be greatest or weakest along all fault lines, which isn't the case.

    • Oh, I'd also like to point out, just for the sake of inflammatory goodness on the interwebs, that America is entirely green and homogenous, thus scientifically proving that we are the best at gravity as well as everything else. Also, we officially qualify as normal and neutral so take that all you backwards-ass, long-haired, rock-and-roll loving, high/low gravity hippy nutjobs on the rest of the continents! Give me back my 9.806 m/s^2 .... I mean...32.174 ft/sec^2....aww hell, I made it back to my OP.

      • Re: (Score:2)

        by jlar ( 584848 )

        "I'd also like to point out, just for the sake of inflammatory goodness on the interwebs, that America is entirely green and homogenous, thus scientifically proving that we are the best at gravity as well as everything else."

        Please take a look at central Africa and tell me again that green and homogenous is a sign that you are best at gravity as well as everything else;-)

    • Heat. Hot rock is less dense than (similar) cold rock, so if you have a lot of hot rock near the surface you are going to have a gravity low (which appears as a "high" elevation on this map). In theory, anyway. I would have expected a much stronger signal all along the MORs; this doesn't appear to be the case.

      Obviously there are many other factors too, but that can explain a tendency towards higher elevations (weaker gravity) in volcanic regions.

    • I wondered that too, but if you look at a volcano map [si.edu], it doesn't seem to correspond very well with high volcanic areas. Compare the areas in Africa and Central America that still have active volcanoes, even though they are not high gravity. The map doesn't correspond at all to plate tectonics, as far as I can tell from my limited understanding.

      It DOES however seem to correspond fairly well with this map of the earth's deformation [wikipedia.org]. Places on the earth that have a surface distance farther from the middl

    • Re: (Score:3, Interesting)

      by CaroKann ( 795685 )
      It looks like there could also be a relation to continental movements in some areas. The cooler colored areas appear to be trailing behind fast moving continental plates, almost like a backwash. Look at the southern tip of India, which is quickly moving north into Asia. There is a cool area to the south of the California plate, which is moving north. There is another cool area off the east coast of North America and to the east of the Caribbean.

  • Got KML? (Score:4, Interesting)

    by BigDXLT ( 1218924 ) on Monday June 28, 2010 @05:55PM (#32724020)
    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.

    • So, the greatest danger to mankind isn't the LHC creating a black hole, it's the Arsenal changing rooms... For the same reason?

      I would never have expected that. (Spanish Inquisition jokes on a postcard, please!)

  • The U.S. military already has one of these (Score:4, Informative)

    by tlambert ( 566799 ) on Monday June 28, 2010 @06:00PM (#32724076)

    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 [scientificblogging.com]

    -- Terry

    • What satellite/aircraft did the US military use to obtain the data at a higher resolution?

      • They don't necessarily have higher resolution data everywhere.

        • Exactly (Score:3, Informative)

          by tlambert ( 566799 )

          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

    • > Interestingly, the inertial navigation software itself is available as source code for download

      [[Citation Needed]]

    • Re: (Score:1)

      by ningeo ( 1022283 )
      I've used this data in the past: http://earth-info.nga.mil/GandG/ [nga.mil]

      I suspect the data available there shares at least some common ancestry with the stuff used in the weapons systems you refer to. Fortunately for us, they recognize it also has value for academia and industry.

  • 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.
    • 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

    • I believe this data is higher resolution than what was available to the public via the GRACE project. That said, the first thing I thought when I saw this was "why is this new?"

    • Re:wonder why they duplciated US GRACE satellite? (Score:4, Interesting)

      by mbone ( 558574 ) on Monday June 28, 2010 @10:19PM (#32726056)

      Grace and GOCE are completely different experiments, which measure different (but related) things about the Earth's gravity field. Grace tracks the motions of a pair of satellites, which GOCE uses pairs of accelerometers. Different data types, different measurement errors, different types of systematic errors. I think it is well worth running both experiments.

      • 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/ [nasa.gov] 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

  • 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?

    • Re: (Score:2)

      by mbone ( 558574 )

      The data is a model of what sea level would be, for a completely water covered Earth, assuming that the oceans had uniform density and no currents, minus the mean sea level. This sounds complicated, but it is pretty easy to calculate, assuming you have the gravity data.

  • Looks like R'lyeh lies beneath the Indian ocean...

  • 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?

    • Looks like someone's going to be made a democracy here soon!

    • Re: (Score:2)

      by mbone ( 558574 )

      The easiest way to find oil in gravity maps from what I understand is to look for salt domes (big bubbles of salt), which are much less dense than the surrounding rock.

      The big low in the Indian ocean is thought to be related to subduction and may even be a "wake" from the recent passage of the Indian subcontinent as the plate drifted North. I don't think it is a huge salt dome.

  • 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

  • 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?

  • 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 bei

  • ...Why my diets are failing at any rate :)

  • Some background: The Satellite Itself (Score:5, Informative)

    by highways ( 1382025 ) on Tuesday June 29, 2010 @01:24AM (#32727134)

    It's worth taking a read [bbc.co.uk] 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 [sparkfun.com] in your iPhone.

    There's a bit more on how it works in this article [bbc.co.uk].

    Of course, the raw data looks a lots uglier [bbc.co.uk] 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 ;)

    • Re: (Score:3, Interesting)

      by Zoxed ( 676559 )

      > That's some serious engineering precision.

      If that is your cup of tea, then you will be interested in the in-development https://secure.wikimedia.org/wikipedia/en/wiki/Gaia_probe [wikimedia.org] : it will measure arcs of the order of the diameter of a hair from 1000 km away !!

    • Re: (Score:2, Interesting)

      by the_other_chewey ( 1119125 )

      Apparently, the accelerometers themselves (3 pairs of them) are mounted to within one picometre

      No they are not. That is entirely impossible to do, as this is quite a bit smaller than atomar scale.
      Even looking at them with too many photons would already change their position by more than that.

      Their relative position is measured to that precision in service.

  • 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 [wikipedia.org] (I think) and it seems you'd get a 0.003% reduction in weight. I'm going to guess no?
    • Latitude is the most important factor.

      Orbital physics tells us that a launch point near the equator, going west, is the most efficient location.

      But after that, I guess it couldn't hurt
      Not a physicist, but I think the forces at work here are of such a low order that a million other factors would probably be more important for factoring in a new launch location (weather wind, etc).
  • 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?
    • No, the effect on water pressure would be minuscule

      and your depth gauges probably measure depth via pressure and not the absolute distance between your position and the the surface?(pretty sure that's how that works), so it would be inherently self-calibrating
  • 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 [imageshack.us]

    Note: Sorry that this is a poor edit, but I had to use MS Paint! :)

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