By Jonathan Amos
Science correspondent, BBC News, Bergen
It is one of the most exquisite views we have ever had of the Earth.
This colourful new map traces the subtle but all pervasive influence the pull of gravity has across the globe.
Known as a geoid, it essentially defines where the level surface is on our planet; it tells us which way is “up” and which way is “down”. It is drawn from delicate measurements made by Europe’s Goce satellite, which flies so low it comes perilously close to falling out of the sky.
Scientists say the data gathered by the spacecraft will have numerous applications. One key beneficiary will be climate studies because the geoid can help researchers understand better how the great mass of ocean water is moving heat around the world.
The new map was presented here in Norway’s second city at a special Earth observation (EO) symposium dedicated to the data being acquired by Goce and other European Space Agency (Esa) missions.
… Imaginary ball
Launched in 2009, the sleek satellite flies pole to pole at an altitude of just 254.9km – the lowest orbit of any research satellite in operation today.
The spacecraft carries three pairs of precision-built platinum blocks inside its gradiometer instrument that sense accelerations which are as small as 1 part in 10,000,000,000,000 of the gravity experienced on Earth.
This has allowed it to map the almost imperceptible differences in the pull exerted by the mass of the planet from one place to the next – from the great mountain ranges to the deepest ocean trenches.
Two months of observations have now been fashioned into what scientists call the geoid.
…Put a ball on this hypothetical surface and it will not roll – even though it appears to have “slopes”. These slopes can be seen in the colours which mark how the global level diverges from the generalised (an ellipsoid) shape of the Earth.
In the North Atlantic, around Iceland, the level sits about 80m above the surface of the ellipsoid; in the Indian Ocean it sits about 100m below.
The geoid is of paramount interest to oceanographers because it is the shape the world’s seas would adopt if there were no tides, no winds and no currents.
If researchers then subtract the geoid from the actual observed behaviour of the oceans, the scale of these other influences becomes apparent.
This is information critical to climate modellers who try to represent the way the oceans manage the transfer of energy around the planet.
…
http://news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/8767763.stm
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What’s that land mass peeking out from the left margine, Southwest of Hawaii?
Lost continent of Pacificus?
Steve (Paris) says:
June 28, 2010 at 11:02 pm
Would it be presumptious to assume it could also reveal how much mass is gained by ice sheets? Or maybe the ‘science’ is designed not to show that?
Gravimetry can indeed show mass being gained as well as lost by ice sheets. Glaciology is not “designed” to show things in a certain way. If it were so, then why would radar altimetry have been used for so long despite bias’ towards ice sheet gain? Glaciologists have their work shown to the world every day, when a glacier advances we can’t just lie about it. And for the record, it would be presumptious to assume that there will be mass gains by any of the ice sheets considering how much mass is currently being lost by all three ice sheets according to laser altimetry, radar interferometry, Gravimetry and melt modeling. And yes that includes EAIS.
J Fergusson I think you’re on to something. The climate changer’s sea level rise might be a case of cherrys picked from natural low grav fields. This map’s high and low gravity points seem to correspond with Roy Spenser’s temp anomaly map pretty well
My how we have progressed, most land masses were very accurately surveyed for gravity and magnetic anomalies in the nineteen sixties. In australia we used Lockheed Hudson WW2 aircraft with huge sensors hanging off them. The data gathered for specific gravity and magnet anomalies was used to locate our mineral wealth. Now a spy in the sky, the mining companies will be wetting themselves. AGW has no dibs on this satellite, this is a money maker.
Blue means weaker gravitation, red stronger?
If the ball (4), lay on the elipsoid surface (1) it would roll from Sri Lanka to Papua given friction = 0?
I had thought the true shape of the Geoid was classified because that’s the data that cruise missiles use to “know” their altitude above the surface.
Climate ain’t heavy. He’s my brother.
@Philip T. Downman: Blue=stronger, Red=weaker.
See my previous comment (http://wattsupwiththat.com/2010/06/28/21178/#comment-419323).
The map is clearly calibrated in metres, not gravity strength. You can see that from the colour-code strip at the bottom.
Hey, we in the UK and Iceland don’t need to worry about global warming !!
@Philip T. Downman: “If the ball (4), lay on the elipsoid surface (1) it would roll from Sri Lanka to Papua given friction = 0?” Yes.
@kzb: “Hey, we in the UK and Iceland don’t need to worry about global warming !!”. Quite the opposite as we are effectively downhill (potentially speaking) relative to the Indian Ocean!
Is it just me or have others noted that the degree of AGW moonbattery is correlated with a high level of gravity?
Ric Werme says:
June 28, 2010 at 9:45 pm
‘BTW, a standard oil (and other mineral) exploration technique entails detailed surface level gravitometer measurements. Oil is low density, so where the gravitational field is weak there’s a better chance that oil is under foot than in areas with a higher field.’
So that’s what happen to the Rocky Mountain Chain.
Olaf Koenders
June 28, 2010 at 11:13 pm
The earth is an oblate spheroid so the surface at the poles is closer to the center of mass then at the equator. The closer to the mass, the greater the gravitational acceleration.
kzb says:
June 29, 2010 at 6:14 am
The map is clearly calibrated in metres, not gravity strength. You can see that from the colour-code strip at the bottom.
Hey, we in the UK and Iceland don’t need to worry about global warming !!
That bit is obvious but does the geoid run several metres above the Himalayan plateau or several thousand metres below it?
From the article- The spacecraft carries three pairs of precision-built platinum blocks inside its gradiometer instrument that sense accelerations which are as small as 1 part in 10,000,000,000,000 of the gravity experienced on Earth.
Interesting statement that as indirectly noted by: Graham Dick who said at 1:41 am
“5. It is the shape the oceans would take without winds and currents” and the moon? To which I will add; the Sun, Jupiter, Venus and Mars.
Picture the satellite in polar orbit as it traverses the earth from pole to pole and round again. As the satellite comes AND goes in ever varying momentary direct line between the center of these “other” gravitational bodies and the earths, certainly the variance in gravitational accelerations is greater than 1 part in 10,000,000,000,000. Would not the satellite need to be shielded from those very dynamic (due to it’s speed) variances? OR it would need to “sense” them somehow separately to compensate (add or subtract the influence) to derive at a true “Earth only” acceleration measurement?
And:
6. So, comparing sea level and geoid data reveals ocean behaviour
(WHAT? Without centrical force, temp. and salinity variances taken into account?)
7. Gravity changes can betray magma movements under volcanoes
(ONLY volcanoes? and NOT the Earth’s molten iron core?)
8. A precise geoid underpins a universal height system for the world
(“height system” that would tell us what? The distance from the exact center of the Earth to ??? And so?)
Not only am I concerned with the veracity of the data being “generated” by this multi-million euro project but also knowing what the look of a “virtual level Earth” is at a given point in time/space. What use is knowing the “difference” between the real Earth and this computer generated level Earth? Hey, don’t get me wrong. I am all for knowing EVERYTHING! You never know when some abstract piece of data is going to fit into or complete the puzzle. But this “sounds like” a boondoggle OR a tool to prove – – well, almost anything you want. June 29, 2016. NASA “We have determined the oceans are rising globally by 20.39674482901 meters per year by comparing globally averaged ocean hight measurements to our Virtual Flat Earth Model.”
j ferguson says: June 29, 2010 at 4:12 am “If sea level changes are in mm increments, wouldn’t they be lost in terms of reliable measureability in the local conditions and “oscillations” discussed above including some very informative comments?”
sHx says: June 29, 2010 at 3:41 am “What would be the effect on sea level if the density of the matter below the crust varies across the oceans? I tend to think it will be fairly negligible. Several milimeters, rather than several Cms.”
Well, the scale is on the chart, and it goes from -120metres to +100 metres. There are about 200 metres in ‘height’ potential therefore between the Maldives and Indonesia. It’s no wonder therefore that the fastest sea level drop in the world is in the Indian ocean (around 90E 15S, -20mm per year measured by satellite altimetry) and the fastest sea level rise is near Indonesia and the Philippines (around 130E 10N, +20 mm per year). These points may be a couple of thousand miles apart, but there is an effective potential gradient of 200 metres over that distance. So, all other things being equal, water should be slowly emptying out of the Indian ocean through Indonesia into the Pacific. And that’s going to keep on going, I suggest, for a long time – until equilibrium is attained or the gravitational anomaly varies.
To my mind, this gravitational anomaly chart answers one of the mysteries as to why the sea levels in the northern Indian ocean have been declining at the same rate as the western Pacific are rising. It also makes the issue of possible sea level rise around the Maldives look more like a joke (they have been in decline for decades), and the actual sea level rise in the Pacific islands look to be a natural phenomenon that we can do nothing about.
The experiment is quoted as precise to to 0.00000000000098 m/s/s. If that is the case, how are external gravity sources controlled out? Curious Buffoon is Curious.
Nice art. I personally like the large fish off the coast of southern Africa.
So we have two competing explanations of what the colors mean:
AleaJactaEst says:
June 29, 2010 at 12:27 am
“Areas of the earth’s crust where seafloor is being actively created (seafloor rock generally has a higher density than continental rock) show as anomalous highs (over Iceland and tracking the Atlantic tectonic spreading ridge to the south) as well as over the area of Indonesia/Malaysia/heading towards New Zealand which is also tectonically active with creation of new seafloor.
Density lows can bee seen to correlate with sedimentary basins (sedimentary rocks have lower densities than seafloor rock), the very large one south of India being a classic case. The one under the Great Lakes/Souther Canada is also a sedimentary basin.”
vs.
Colin W says:
June 29, 2010 at 2:39 am
“@Policyguy: The map is showing the change in height needed to maintain the same potential energy. So comparing two people of the same mass, one goes to Sri Lanka and another to Iceland. Because the gravity is stronger over Sri Lanka (denser/thicker rock) that person would have to move closer to the centre of the earth relative to the person in Iceland (less dense/thinner rock) to have the same potential energy.
So any water at Sri Lanka with higher potential energy than the surrounding water would move away, like a ball rolling, or rivers flowing, downhill, so we would expect deeper water at Iceland (ie water further from the centre of the Earth) than at Sri Lanka.
Excuse my rusty Physics”
So then the question is; does that mean that warm ocean water roll downhill to the polar regions; or is it more complex than that as the sea surfgace has alrady “levelled out geoidally, exccept for wind tide and current.
And so what is it with all those dark olive areas; that aren’t any of the colors on the scale; what the heck are those ?
Can Michael Mann, now use this geoidometer as a proxy for Temperature anomalies; it would seem to be as well connected as tree rings ?
Interesting, but not new. I have a photograph of the Goddard Space Flight Center Detailed Gravimetric Geoid on display in the Smithsonian in 2003. Less detailed,
and much less colorful, but roughly the same information.
Kieth Minto:
Keith Minto:
There is no such thing as centrifugal force, there is a force called cetripetal force caused by rotation at least according to my physics IV professor who threatened me with an F if I used that term again. Gravity, itself, is not a force, per se, but a curvature of space caused by the presence of mass. Where gravity is “stronger” there is more mass and vice versa. The map shows where mass is concentrated and the gravitational differences are apparently miniscule.
Buffoon says: June 29, 2010 at 9:13 am “The experiment is quoted as precise to to 0.00000000000098 m/s/s. If that is the case, how are external gravity sources controlled out?”
The BBC report says:
“The spacecraft carries three pairs of precision-built platinum blocks inside its gradiometer instrument that sense accelerations which are as small as 1 part in 10,000,000,000,000 of the gravity experienced on Earth.”
That’s highly misleading as it’s a measure of resolution of the sensors individually and not related to the accuracy of the overall instrument. It’s not ‘precise’ or ‘accurate’ to anything like that. Typical ‘gee-whizz’ journalism to use a big number that is meaningless in the context of mission accuracy. By the time the measurements are combined on 3 axes and compensations made for perturbations the mission objective attained is a more believable accuracy of one part per million, i.e. 1 x 10^-5 m/s^2.
Check out ESA’s own useful brochure on the satellite, instruments, and mission objectives:
http://esamultimedia.esa.int/docs/BR209web.pdf
The geoid seems to be a fairly difficult concept for people to grasp, which is understandable because it is a bit counterintuitive. To simplify somewhat, it is an idealized and imaginary approximation of what the surface of the liquid water on the planet would display if all influences other than gravitational anomalies were removed and all land masses were 100% permeable to the water. The blue areas are high gravity and the red are low gravity.
It highlights what a meaningless concept Global Mean Sea Level really is. If you wanted to build a vehicle capable of traversing the world’s oceans exactly at GMSL it would have to be a “Thunderbirds” special which could morph from a submarine able to handle depths greater than a hundred meters to an airplane able to fly at over a hundred meters altitude.
There is a pretty good discussion of the geoid and the reference ellipsoid in the data products handbook for JASON 2
http://www.osdpd.noaa.gov/ml/ocean/J2_handbook_v1-3_no_rev.pdf
And though I usually avoid referencing Wikipedia, their article on the geoid isn’t terrible
http://en.wikipedia.org/wiki/Geoid