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Bolivian Salt Flats Aid Spacecraft Calibration
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.'"
Salar de Uyuni in Google Maps.
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Just a guess, but the note, "less than 80 centimeters variation," would indicate it follows the curve of the earth. If it were flat-flat, it would have a much larger variation than a meter.
Well, OK. You've got an excuse for asking this, since you're drunk. There is no FLAT flat on the earth. The area still shows a horizon which means that it's EARTH flat and not FLAT flat:
http://www.google.com/search?&rls=hi&q=salar+de+uyuni&ie=utf-8&oe=utf-8
I'm an infovore...
Flat in the sense that every point on the surface is equidistant from the earth's center of mass.
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No. It means every point is at the same gravitational potential, and the equipotential surfaces are not spheres. Close, but different.
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
Jesus effing Christ, everybody on this thread seems to be drunk.
Go to Wikipedia and figure 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.
I'm an infovore...
Minor correction. The most recent Land Speed records were set on the Black Rock Desert. Prior to this almost all of them were done on the Bonneville salt. From the Wikipedia article;
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)
Trying to associate Microsoft with "fun" is like trying to associate Satan with aromatherapy. -Tycho
As the other poster mentioned, the two locations have varying sizes.
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/
No, extremely small. Over an area that small, you can pretty well assume the equipotential surface is a sphere.
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
As others have said, the size of the Bolivian salt flats is the thing here. And they're not just big in the sense that you can measure them as larger than bonneville, they're big as in "go to google earth and see the huge white splotch on south america" big.
http://www.danamania.com/tmp/salar.jpg for a pic.