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Bolivian Salt Flats Aid Spacecraft Calibration
Posted by
Zonk
on Sat Dec 01, 2007 08:17 PM
from the wait-just-one-okay-wait-no-wait-i'll-get-it-wait-hold-on-okay-wait dept.
from the wait-just-one-okay-wait-no-wait-i'll-get-it-wait-hold-on-okay-wait dept.
PCOL writes "Salar de Uyuni is a vast plain of white salt in the mountains of Bolivia, with a total elevation range of less than 80 centimeters - the flattest place on earth. Beginning in 2002, geophysicist Adrian Borsa led a survey that resulted in precise GPS measurements of the salt flat. The flats will be used as a giant calibration device for satellite-based radar and laser altimeters on the CryoSat recovery mission so the spacecraft can more precisely monitor changes in the elevation and thickness of polar ice sheets and floating sea ice. 'Satellites can calibrate their altimeters by bouncing signals off the ocean surface .. because of atmospheric interference, tides and waves, there are uncertainties. Borsa says the salar, now so accurately mapped and with dry, clear skies, is about five times better than the ocean as a reference point.'"
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Google Maps Link (Score:5, Informative)
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Re:Google Maps Link (Score:5, Funny)
Hi res satellite image [about]
Parent
wierd (Score:2)
Either that or some sort of weird shrub.
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i've got a bad feeling about this... (Score:5, Funny)
Many Bolivians died to bring us this information.
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Evil Supergeniouses (Score:3, Funny)
Hey. It's more credible than Goldeneye.
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Alternatives (Score:3, Funny)
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It's Saturday night (Score:5, Interesting)
When they mean that it's the "flattest place on Earth", do they mean that it conforms exactly to the curvature of the earth (thus not REALLY flat but earth shaped sort of flat), or is it FLAT flat, as in a chord across the curvature of the earth at that point...
Sorry, just trying to work out the meaning of "flat" on a round planet... blame the rum.
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Re:It's Saturday night (Score:4, Interesting)
In order to be straight line flat, the elevation would have to vary something like 200 meters, based on some rough calculations I did in trying to thing about this. Basically, I assumed that the salt flat is ~100km across, so the each edge is ~50km from the center, and would have an elevation given by the right triangle formed by the radius from the center of the earth and a 50km tangent line(the hypotenuse would be the elevation at the edge). (6300**2+50**2)**0.5=6300.198, subtract the radius, and you are left with 0.198 km, or ~200 meters). This is a simple model of the earth's shape, but it's within a factor of 3 or something.
Parent
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http://www.google.com/search?&rls=hi&q=salar+de+uyuni&ie=utf-8&oe=utf-8 [google.com]
Re:It's Saturday night (Score:5, Informative)
Go to Wikipedia [wikipedia.org] and figure [wikimedia.org] it out yourself. Or better yet: go to bed and sleep. Look out of the window when you wake up tomorrow and try to find out why on earth you're not seeing the Chinamen in the far distance.
Parent
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Disclamer: I'm a member of a people that had been enslaved for about 500 years and hence I know how it feels like when 50% of your ancestors died in liberation attempts and your petty nation is ridiculed by both the West and its fo
Re:It's Saturday night (Score:5, Informative)
Flat in the sense that every point on the surface is equidistant from the earth's center of mass.
Parent
Re:It's Saturday night (Score:5, Informative)
For example, Mt. Chimborazu in Ecuador, 21000 feet above the equipotential surface we call "mean sea level", is farther from the center of the earth than Everest at 29000 feet.
Bear in mind these are small differences: if you could make a perfect scale model of the sea-level surface the size of a billiard ball, it would be rounder and smoother than the ball.
rj
Parent
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True in general because the earth doesn't have uniform density. Over an area as small as even the Bolivian salt flat, though, is the difference likely to be at all significant?
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Sorry to reply to my own post, but I realized there's another issue, and it might be the more significant one -- the earth is closer to an ellipsoid than a sphere. Still I expect that over a small area a sphere is a *very* close approximation.
Re:It's Saturday night (Score:5, Informative)
The reason for the flatness of salt flats is that the salt gets soupy in the rainy season, gravity smooths it out, and then the water evaporates out leaving a hard surface -- although if there's a substantial prevailing wind during the wet season, you get some deviations.
rj
Parent
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Yes. In fact, the article itself points out that there are bumps in the surface due to large rock formations a few km below the surface.
The surface of the ocean varies hugely from a sphere over the mid-oceanic ridges. Precisely mapping the sea surface height allows us to deduce the relief of the ocean floors. Check out the front cover picture of Mapping the Next Millenium: The Discovery of N
Re:It's Saturday night (Score:5, Interesting)
Mind if be pedantic? Not quite true. The difference between pole and equatorial radii at sea level is 22 km. Add in the height of Mt Chimborazu and the depth of the ocean near the South Pole, and we find that Earth deviates from a sphere by about 33 km, and so it's spherical to within +/- 0.26%.
The Billiard Congress of America [pool-table-rules.com] requires billiard balls to be 2.25" in diameter, to an accuracy of +/- 0.005", or +/-
So, the Earth doesn't quite pass muster as a billiard ball.
"Give me a pool cue large enough and a place to stand, and I shall sink the Earth in the corner pocket." -- Archimedes Fats
Parent
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Re:It's Saturday night (Score:5, Interesting)
Here's to spending way too much time playing with GPS! Cheers!
Parent
the calibration would've gone faster... (Score:2)
Tearing it up (Score:5, Interesting)
oblig simpsons quote (Score:1)
If it is used for Calibration right now... (Score:3, Interesting)
Wow (Score:3, Funny)
In other news, Adrian Borsa* has the most boring and tedious job on the planet.
*Or his grad students
And sitting in a cubicle isn't boring? (Score:3, Insightful)
While you are probably looking for a quick "Funny" rating, a serious look reveals that, sadly, doing a GPS survey of some god-forsaken salt flats probably *is* more exciting than many ordinary jobs.
50 years from now you will have forgotten what you did, but some geophysicist will be able to say "Oh, yeah, back in ought-two, I was part of a team that had an all expense paid trip to Bolivia to hang out and sample the local cerv
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Using the Bolivian Salt flats (Score:2, Funny)
The Great Salt Flats in Utah are flatter... (Score:5, Interesting)
And every year it gets 'reset'... The springtime runoff from the surrounding mountains will cover the entire salt flats with a perfect 1/2" of water. It is SO COOOL to go out there when there is a *PERFECT* sheet of water covering the salt, it looks like the worlds largest piece of glass. You can actually *SEE* the curvature of the earth. I have a picture of a much younger me 'walking on water' because it is so smooth you cannot tell that the water is only 1/2" (1.5cm) deep.
Working out on the salt flats, doing surveys, the survey crew would drive out 1 mile and hold up a survey marker. At five miles out we could not see them any more, we asked them to raise it up over their heads and we saw the marker rise up over the horizon like it was the sun coming up.
Because it is the worlds largest and flattest spot on earth, my father, an engineer in flight optics systems, has built optical calibration targets used by the military to calibrate autopilot systems, weapons guidance systems, terrain following radar systems, satellite optics systems and all that jazz for the military... which is why I grew up in Utah, am intimately familiar with the flats, and know without a doubt that my dad has worked on black projects that I hope someday he'll be able to tell me about (including flights into and out of the Janet terminal).
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Richard Noble,
October 4 1983, Thrust2, 633.468mph (1019.47kph) Record stood for 13 years
September 25 1997, ThrustSSC, 763.035mph (1227.99kph) Sound barrier broken - (Mach 1.016)
Re:The Great Salt Flats in Utah are flatter... (Score:5, Informative)
You are looking at an area of 10,582 km (Salar de Uyuni) versus an area of 412 km (Bonneville Salt Flats).
In fact, you are most likely correct about the Bonneville Salt Flats having no more than 1 foot (30 cm) of elevation variation for every 10 miles (16 km), however, the Salar de Uyuni was found to have only 16 inches (40 cm) of variation over its entire surface. This is a huge area that dwarfs 10 miles. The Salar de Uyuni has also been stated by several places that it is, indeed, the largest flattest surface yet to have been found on earth.
Purely speculation on my end however, would be the reasons why the military would choose the Bonneville Salt Flats over the Salar de Uyuni. The military would most likely be testing equipment and technologies they don't want anyone else to get their hands one or are a type which are particularly politically sensitive, whereas other space or research agencies are more or less politically neutral comparatively. This allows other groups to test in an international (and further away) location that the military might find inconvenient due to both political and logistical reasons. Stating that because a lot of people do testing on the Bonneville Salt Flats is not evidence for it being the flattest. There are reasons to use it, simply because of its convenience and close location (it is in US compared to being in Bolivia) among other things.
Read more on the Bolivian Salt Flats (Salar de Uyuni).
http://dsc.discovery.com/news/briefs/20041206/flatearth.html/ [discovery.com]
Parent
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I assume you're not factoring in the few 'islands' dotted around the Salar de Uyuni.
It's a very interesting place to visit. My (now) wife and I went there in 2005 on our trip around South America. For two months of the year it rains steadily and the whole area floods to about 30-50 cm (going from memory here). The water evaporates for the next few months, leaving a bed of salt. We went there in the last few week
Pic of just how big the Bolivian flats are. (Score:3, Informative)
http://www.danamania.com/tmp/salar.jpg [danamania.com] for a pic.
Re:The Great Salt Flats in Utah are *not* flatter (Score:3, Interesting)
If this is accurate (and it does appear to be), Bolivia is much, much bigger. You could lose Bonneville salt flats in Bolivia. I would also further speculate that both locations are equally flat as the salt will form a flat, equally distributed surface whenever it rains. I know from survey after survey that the Bonneville Salt Flats are within the margin of error for the measuring equipment to even detect variati
In other words... (Score:5, Funny)
Ocean measurement have to be taken with a grain of salt, but these - oh wait.
Tag (Score:5, Funny)
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But now the tag has gone. I didn't know they could be deleted.
Similar calibration for imaging sensors too... (Score:2, Interesting)
Calibrating spy satellites (Score:2)
Envisats LRR (Score:2)
Sounds more complicated then Envisats LRR (mirror on spacecraft, bounce a land based laser off it and measure the round trip time: http://envisat.esa.int/instruments/lrr/ [esa.int])
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They're trying hard to be!