Researchers Develop the Most Detailed Map of Gravitational Variations Ever 88
schliz writes "An Australian-German team of researchers has developed the most detailed map of gravitational variations ever, using satellite data, gravitational readings and small-scale topographical models. They say the data will help civil engineers and miners, and will be available for free online. Gravitational fields vary because the Earth isn't perfectly spherical. According to the new map, the field is 0.7% greater near the North Pole (9.83ms-2) than at Peru's Nevado Huascaran summit (9.76ms-2). The difference is 40% more than previously expected."
direct link (Score:5, Informative)
Here is a direct link to the map [curtin.edu.au] if you are wondering where you'll be the lightest :)
Re:direct link (Score:5, Funny)
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Hey. Don't make light of the gravity of this research.
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It's nice to hear that another country has found a fair and balanced way to quantify "good work." because here in the US it's all about what you can convince someone as "good work" leading to requiring far more political/sales/marketing skills and the research itself is secondary to that.
So what is the fair and balanced weighting of "good work" to which you employee?
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Probably should be most detailed map released to the public. The Military of both the US and Russia/USSR have been working on maps of gravitational variations for decades.
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Civilian uses for high resolution maps include mineral prospecting.
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Probably should be most detailed map released to the public. The Military of both the US and Russia/USSR have been working on maps of gravitational variations for decades.
It would also be only the most detailed measured using sattelites. More detailed maps can be made using measurements from airborne gravimeters or surface measurements. They are used often for oil and mineral exploration.
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Here is a direct link to the map [curtin.edu.au] if you are wondering where you'll be the lightest :)
Where is the lowest spot?
http://physics.stackexchange.com/questions/22613/lowest-gravity-on-earths-surface [stackexchange.com]
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Your Mom's House (Score:5, Funny)
Re: Your Mom's House (Score:2, Informative)
Actually the opposite is true. The more mass you have between the gravity source and your self the lower the gravitational pull is.
Though why Everest has higher gravity than a mountain in Peru is odd. Unless the lost city of gold is under that mountain.
The bigger the object the greater the gravitational field. However the more mass you have between yourself and said field point"source" the lower the effects of gravity you feel.
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The more mass you have between the gravity source and your self the lower the gravitational pull is
That doesn't make any sense to me.. mass is your "gravity source". Though due to the inverse square nature of gravitational pull, putting yourself on top of a mountain would probably reduce the overall gravitational force exerted on your body much more than it adds to it (owing to you getting further from the centre of the Earth). Especially if the mountain was tall, thin, and had a low density.
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No mass isn't the gravitational source by itself. There is another link between the two. Yes the higher the mass the higher the gravity. but this map shows you can get fluctuations in gravity's acceleration not only based on altitude as expected, but densities or other sources.
As a mountain that is 7,000' shorter than everest has less gravitational pull. Look at that map. areas that are volcanic have greater gravitational pull.
Something else is affected the expected numbers. density of the mantle is a
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Being on top of a higher mountain places you further from the all that mass of the whole planet, reducing your gravity. How it is that they are showing higher gravity for some mountains is not understood.
Re: Your Mom's House (Score:4, Interesting)
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Agreed. From the map they're obviously not just measuring altitude and running it through Newton's equation with R being the distance to the center of the Earth. Or maybe they are if the world isn't perfectly elliptical (as noted in the article). If the Peruvian mountains are tall but overall set in a portion of Earth closer to the center of mass, then their gravity at the peak might be stronger than other equally high mountains. Or maybe they are taking into account on site measurements as well. A sat
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If you RTFA [curtin.edu.au]...
All quantities are given at the Earth’s surface as defined through the SRTM (Shuttle Radar
421 Topography Mission) topography. Users wishing to use geoid heights instead of quasigeoid
422 heights can do so by applying standard conversion as described, e.g., Rapp [1997].
If you want a more generic explanation of gravity anomalies? Perhaps this will help... http://www.cage.curtin.edu.au/~will/grav_anoms.htm [curtin.edu.au]
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I'm still hoping for an anti-gravity cloak
It could cause problems for you to not be attracted to the sun, or the centre of our galaxy, etc :D
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the extra mass of the mountain...
...is at least partly compensated for. It's not just "some extra stuff on top of something that exactly the same as places without extra stuff on top": the mountains float on the denser mantle with the rest of the Earth's crust, with a greater portion of the lighter crust material reaching deeper into the mantle, creating a "negative mascon" under the "extra mountain". It's somewhat like ice on sea - there's light stuff under the surface, too.
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They say it's a "gravitational map" but is it with or without the effects of the earth's rotation? How much less do you weigh because the earth's rotation is trying to fling you off it on a mountain top (longer radius arm) near the equator (faster rotational speed)?
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Look up Newtons Theorem and try again.
Re: Your Mom's House (Score:2)
The survey shows that is wrong. Everest has greater gravity acceleration than a mountain 7,000 ' shorter.
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I am not mad about your joke at my mothers expense, just that I was going to make the same joke about my ex-wife!
Comment removed (Score:5, Funny)
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the more challenging and involved effort will be the calculus of integrating this detailed graviton map into future "your mother is so fat" jokes.
Your mother is so fat, she has a uniform gravitational field.
Don't know their science (Score:3, Informative)
From the article: That means a 100kg person weighs 700g more near the North Pole, where gravity is 9.83ms-2, than at Peru’s Nevado Huascaran summit, where gravity is 9.76ms-2.
They are implying that mass is a function of gravity. Everybody who has had the most basic fundamentals of physics knows that mass doesn't change, only weight(measured in newtons)
Re:Don't know their science (Score:4, Insightful)
Grocery stores "weigh" everything in grams. Grams might be mass but the general populace uses mass interchangeably with weight.
Hmm, can we use the map to get global scale calibrations to a normal mass. It would seem to be unfair that the same amount of material might cost more or less in different places due to scale errors that measure weight and use it blindly as mass.
Re:Don't know their science (Score:5, Interesting)
Hmm, can we use the map to get global scale calibrations to a normal mass. It would seem to be unfair that the same amount of material might cost more or less in different places due to scale errors that measure weight and use it blindly as mass.
For weights that are comparing against a known mass there is no problem. The 1 kg of material you want to buy will always weigh the same as the 1 kg on the other side of the scale weight, no matter if it's 9.76 or 9.83 newtons on each side. So these "global scale calibrations" just involve transferring around known masses and has been done for centuries. The only way the scale would be off would be if one arm was on the North Pole and the other in Peru.
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but my scale is really really big. Spanning form west to east Venezuela.
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For weights that are comparing against a known mass there is no problem. The 1 kg of material you want to buy will always weigh the same as the 1 kg on the other side of the scale weight ...
True, but not all scales work that way. Many use a spring or pressure sensor rather than comparing weights directly, and thus wouldn't take variations in the gravitational field into account. These scales would need to be calibrated against a known mass if they were used in a different location than they were manufactured in. (Of course, they probably needed to be calibrated anyway...)
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Yes, I'm immediately taking this map to my drug dealer. I've been wondering for years why he will only let me make buys on Easter island... now it's become rather clear that I'm being ripped off.
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In other news, purchasing drugs in Peru and selling at the North Pole for profit! Someone has to keep those elves peppy.
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Secretly, regular people who live in SI countries don't use or understand Newtons unless they're scientists.
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Yep. I regularly tell people I weigh 885 Newtons
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Fig or strawberry?
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Its 2013, how many IPADs is that!
The Newton is so 90's.
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From the article: That means a 100kg person weighs 700g more near the North Pole, where gravity is 9.83ms-2, than at Peru’s Nevado Huascaran summit, where gravity is 9.76ms-2.
They are implying that mass is a function of gravity
Not really. They specifically say "weighs", which is weight, not "masses".
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Actually, they are not. No one thinks mass depends on gravity. What the article actually says is:
That means a 100kg person weighs 700g more near the North Pole
Weighs 700g more. Weighs. They are merely saying that weight is a function of gravity, which is of course, true.
You are confused by the units they are using. This is actually the kilogram-force [wikipedia.org], a non-SI unit of weight, which converts to about 9.8N or 2.2lb. Cool, no?
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That means a 100kg person weighs 700g more near the North Pole
You are confused by the units they are using. This is actually the kilogram-force [wikipedia.org], a non-SI unit of weight...
Anyone would be confused by their units. Even if they did mean to refer to the kilogram-force (why?) they still got it wrong. The shorthand for kilogram-force is "kgf" or "kp", not "kg" or "g". The article's "700g" is a measure of mass, not weight.
Better: A 100.0kg person at the North Pole weighs the same as a 100.7kg person at Peru's Nevado Huascaran summit.
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How much of an effect does centripetal force play here? Gravity is the centripetal force at the equator that keeps people from flying off the earth due to their tangential velocity. So the perceived gravity on the equator should be less, right?
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Seconds as a unit of Isp is nice because it tells you how many seconds of e.g. 1 lb force thrust you get for 1 lb mass of fuel. (Or conversely, how many pounds force you get from that 1 lb mass of fuel if you burn it all in one second.) It's a handy comparison number.
Granted it's kind of an odd unit if you're trying to work out trajectories and mass ratios and delta-vees and such, but hey, it's not rocket science.
Oh, wait...
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Indeed,
The US, the French and probably the Russians have their own classified gravity maps. Essential to improve inertial guidance of ICBMs so the ones launched by submarines match the precision of ground based ones. I had a colleague whose works on acoustics where classified by NATO. It means he was forbidden to publish his work. I Guess this hasn't changed a lot and that a too precise gravity map could not be released even today.
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In absolute it may be innacurate, but it may still be the most detailed ever in the sens of published work available to the public. The publication / availability of information is a critical factor for scienctifc work.
No scientific work is complete before it has been published and peer reviewed.
Ground Truth? (Score:2)
I wouldn't dare use this "map" for any serious purposes. It appears all they did was add the fine details from a topographic map to the rather low resolution results of other surveys. There's no high resolution direct measurement of gravity here.
Don't match (Score:1)
Why the two images in the post don't match?
no key or legend (Score:3)
it's great and all that they posted a pretty picture [curtin.edu.au] but they forgot to add a key or a legend of some kind. a color gradient scale with some kind of metric is the least they could do, even the weather channel knows that! [weather.com]
i'm sure the people who made this are the same damn kids that keep walking on my! </rant>
Re:no key or legend (Score:4, Informative)
Of course there isn't. That's why boats float.
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They had a scale in the first article [alluremedia.com.au]. You can probably make your own using the tool.
torrent? (Score:1)
It would be fun to play with this data.
Anyone have a torrent?
Bah (Score:2)
"Gravitational fields vary because the Earth isn't perfectly spherical."
Uhm, not just that. Gravitational fields also vary because different places on Earth (or other bodies, for that matter) have materials with different density under them, forming so-called mascons.
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Also, the variation is measured relative to the reference ellipsoid rather than a sphere.
Only Google Earth thinks that the reference shape for the Earth is a sphere. Unfortunately, everyone wants their systems to work with Google Earth, so everyone has basically copied the mistake. Lars is thus responsible for effectively undoing 400 years of geography.
Best ever? (Score:2)
Folks who fly ICBM's need very accurate masscon (mass concentration) maps for guidance. So I'll bet that various governments militaries have more accurate maps. They do, after all, have a bevy of satellites whose orbit perturbations allow the computation of such things to any degree of accuracy desired ;>
Whether they make displays as nice, I don't know.
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Do people actually actively guide ICBMs? I'd figured they were completely automated. And, how accurate do you need to be with a nuke?
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The more accurate you can make the nuke, the smaller it can be. Saves you nuclear materials and launch weight.
And against hardened targets like missile silos or command bunkers, pretty accurate (eg, Cheyenne Mountain couldn't withstand a direct hit, but it could a nearby miss. Colorado Springs would be toast either way.)
ICBMs are pretty much autonomous once launched (I would assume/hope they have an abort mode), but their targeting data is updated regularly (especially true for sub-launched missiles, of c
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That's a reasonable point on the atmospheric effects of reentry, but that's only in the last couple of hundred miles, so any angular deflection will have a lower effect on the CEP than would even a smaller deflection closer to the launch. Over a few thousand miles, a slight angle change makes a big difference.
And, you're assuming the reentry is unguided. That isn't necessarily the case. Even a simple cone can have some crossrange depending on the relation of center of mass vs center of aerodynamic pressu
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"Folks who fly ICBM's need very accurate masscon (mass concentration) maps for guidance."
Or what? The 10 Mt ICBM will boom 10 m out of its target on the other side of the world?
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ho hum... (Score:2)
maybe I'm not understanding the situation of the gravity here.
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From Newton, the gravitational potential from a point source is mass*G/distance. With topography, there are two things acting. Because mountains are high, they are further away from the Earth's center of mass (typically, the Earth's gravitational potential map is modeled as a multipole expansion of Legendre polynomials centered at point source at the center of the earth).
However, there is also the gravity of the mountain(s) itself pulling you down. In most mountain ranges, there is lower gravity because of
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Also, looking at the world map, it is a map of Bougeur anomalies (or using some other correction), which are gravitational anomalies corrected for the elevation they are taken at and the mass of the topography. That is why a good portion of mountainous areas are shown in red.
The map of Australia is just straight-up gravity (and is different from Australia in the global anomaly map).