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Space Science

Bolivian Salt Flats Aid Spacecraft Calibration 98

Posted by Zonk
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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Bolivian Salt Flats Aid Spacecraft Calibration

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  • Google Maps Link (Score:5, Informative)

    by SeanTobin (138474) <byrdhuntr@hotCOWmail.com minus herbivore> on Saturday December 01, 2007 @09:29PM (#21548555)
    Salar de Uyuni [google.com] in Google Maps.
  • by User 956 (568564) on Saturday December 01, 2007 @09:32PM (#21548565) Homepage
    Bolivian Salt Flats Aid Spacecraft Calibration

    Many Bolivians died to bring us this information.
  • by Protonk (599901) on Saturday December 01, 2007 @09:33PM (#21548573) Homepage
    How long until the League of Evil (or some such nonsense) invents a dastardly plan to mess with satellite location calibration by digging giant holes in the salt flats?

    Hey. It's more credible than Goldeneye. :)
    • by Ziwcam (766621)
      They won't have to. TFA (one of them, at least) mentioned that the area floods every 5 years or so, causing the salt to realign itself. I would imagine this changes the height, and the distribution of the high and low areas in the plane.
    • Re: (Score:3, Interesting)

      by barakn (641218)
      I've been there. It's already being mined for salt. Not only do they leave holes but they leave the salt in conical piles to dry out (the water table is quite close and actually pools on the surface in some locations).
  • by Anonymous Coward on Saturday December 01, 2007 @09:33PM (#21548575)
    Didn't anyone tell these guys about the Netherlands?

    • Re: (Score:2, Funny)

      by Anonymous Coward

      Didn't anyone tell these guys about the Netherlands?
      Yeah, but the Netherlands would probably make arrays to catch all of the energy being directed from space so that they could reduce their CO2 output even more. And that sort of defeats the purpose. Why would you make a fancy satellite to measure ice loss if the Netherlands is trying to stop it (both the radar calibration and the ice loss).
  • It's Saturday night (Score:5, Interesting)

    by Dunbal (464142) on Saturday December 01, 2007 @09:38PM (#21548617)
    And I have probably had a bit too much to drink, so forgive the deeply philosophical question.

          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.
    • by Bl4d3 (697638)
      Good question! The beer and snaps hasn't cleared out yet so I want to know it to.
    • Re: (Score:3, Informative)

      by Rolgar (556636)
      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.
      • by maxume (22995) on Saturday December 01, 2007 @10:14PM (#21548819)
        It is somewhat important that the article mentions the 80cm variation in terms of elevation.

        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.
    • Re: (Score:2, Informative)

      by Mantaar (1139339)
      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 [google.com]
      • by maxume (22995)
        Please explain why a flat flat would not have a horizon.

        Keep in mind that I might have had a few.
        • by Mantaar (1139339) on Saturday December 01, 2007 @10:46PM (#21548937) Homepage
          Jesus effing Christ, everybody on this thread seems to be drunk.

          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.
          • by MiniMike (234881)
            I hope for your sake he's not in China...

          • by flynns (639641)
            Seriously. Also, Dude, 'Chinama' is not the preferred nomenclature. Asian-American, please.
          • by maxume (22995)
            I meant a flat flat set down on top of the globe. There would still be a horizon.
            • by Mantaar (1139339)
              That's why I linked to the google search. One of the first hits is this beautiful picture [tripod.com] - if it was FLAT flat you'd see some mountains in the distance since you'd just have to see something that's not the salt lake. But you don't. In fact, you only see the sky. Really beutiful shot, btw.
              • by maxume (22995)
                You implied that a flat flat wouldn't have a horizon. I was hassling you about it. Clearly you meant that a flat flat wouldn't have a curved horizon.
    • FTA: "You see the horizon, the curvature of Earth. It's absolutely featureless."
    • by swillden (191260) <shawn-ds@willden.org> on Saturday December 01, 2007 @10:07PM (#21548787) Homepage Journal

      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...

      Flat in the sense that every point on the surface is equidistant from the earth's center of mass.

      • by Deadstick (535032) on Saturday December 01, 2007 @10:34PM (#21548905)
        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
        • by swillden (191260)

          No. It means every point is at the same gravitational potential, and the equipotential surfaces are not spheres. Close, but different.

          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?

          • by swillden (191260)

            True in general because the earth doesn't have uniform density.

            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.

          • by Deadstick (535032) on Sunday December 02, 2007 @01:03AM (#21549621)
            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
          • by phliar (87116)

            Over an area as small as even the Bolivian salt flat, though, is the difference likely to be at all significant?

            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

        • by goodmanj (234846) on Sunday December 02, 2007 @03:54AM (#21550279)
          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.

          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 +/- .022%.

          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
    • by TimeTraveler1884 (832874) on Saturday December 01, 2007 @10:15PM (#21548829)
      Usually when anything of a GIS nature refers to something as "flat", it is in relation to the WGS84 [wikipedia.org]. My understanding is that geodetic systems basically project an perfect, elliptical sphere around the the gravitational center on earth. But I probably have had too much to drink myself so don't hold me to it.

      Here's to spending way too much time playing with GPS! Cheers!

    • by AikonMGB (1013995)

      I suspect they mean flat as in it conforms to the curvature of the Earth. Having said that, my guess is that the areas they are dealing with are small enough that this curvature may be neglected.

      Aikon-

    • I have an unopened beer sitting in front of me, and I had the very same question, so don't blame the booze! ;)

  • ...if the Bolivian navy hadn't been on maneuvers in the South Pacific.
  • Tearing it up (Score:5, Interesting)

    by BWJones (18351) * on Saturday December 01, 2007 @09:42PM (#21548643) Homepage Journal
    Yeah, just don't let Boyd Coddington anywhere near those salt flats. Look what he did to the Bonneville Salt Flats [nsra.org.uk] this year when I was out taking photos [utah.edu].
  • "in the event of nuclear war, the bolivian salt flats will be designated nuclear whipping boy and have test nukes fired for calibration"
  • by Sique (173459) on Saturday December 01, 2007 @09:49PM (#21548671) Homepage
    ... doesn't that mean that if anyone started mining the salt there, all navigational devices are hosed, because there is no normal anymore to calibrate them?
  • Wow (Score:3, Funny)

    by moosesocks (264553) on Saturday December 01, 2007 @09:56PM (#21548727) Homepage

    "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


    In other news, Adrian Borsa* has the most boring and tedious job on the planet.

    *Or his grad students
    • lol, I appreciate the humor, and I am self employed, not even a cubicle worker.

      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

      • by timmarhy (659436)
        unlikely, surveying is a tidious boring fucker of a job. I'm betting it's boiling hot during the day and freezing at night.

        he will be taking 100's of measurements and compiling a list of them, nothing exciting about it. I'll keep my comfortable chair and aircon thanks.

        • by BeeRockxs (782462)
          It is pretty fucking cold at night, but not boiling hot during the day. When I was there I even wore my sweater.
  • What? and Bolivia won't be able to charge anyone for this service? It is really unfair to this poor country to be used and exploited like a flat chested woman....
  • That's in Utah, right?

    Is Europe a country?
  • by JRHelgeson (576325) on Saturday December 01, 2007 @11:17PM (#21549089) Homepage Journal
    The dried Bonneville Salt Flats (open to the public) and its attached military only area called the Dougway Proving Grounds are the flattest place on earth. They have been used by the military for the past 40+ years to calibrate space and weapons systems. Pretty much every land speed record has been made at the Bonneville Salt Flats, including breaking the sound barrier. The variation of altitude is so minimal that it is within the accuracy of the measurement equipment used to calibrate altitude variations, but it has been certified to be less than 1 foot of elevation for every 10 miles.

    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).
    • Re: (Score:2, Informative)

      by mad zambian (816201)
      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 [wikipedia.org];
      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)
    • by Anonymous Coward on Sunday December 02, 2007 @12:34AM (#21549483)
      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/ [discovery.com]
      • the Salar de Uyuni was found to have only 16 inches (40 cm) of variation over its entire surface

        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
    • 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 [danamania.com] for a pic.

  • by fahrbot-bot (874524) on Sunday December 02, 2007 @12:03AM (#21549335)
    Satellites can calibrate their altimeters by bouncing signals off the ocean surface .. because of atmospheric interference, tides and waves, there are uncertainties.

    Ocean measurement have to be taken with a grain of salt, but these - oh wait.

  • Tag (Score:5, Funny)

    by Hemogoblin (982564) on Sunday December 02, 2007 @12:09AM (#21549377)
    Only on Slashdot would a story about "calibration of equipment using saltflats" be tagged as ReallyFuckingCool. :D
    • Only on Slashdot would a story about "calibration of equipment using saltflats" be tagged as ReallyFuckingCool

      But now the tag has gone. I didn't know they could be deleted.

  • I had a remote sensing professor at the University of Arizona that frequently took road trips with his students out to remote areas in Nevada to calibrate imaging sensors. For this, the absolute flatness isn't as important as the high reflectance of the dry lake beds they use. Here [arizona.edu] is more info.
  • Once I visited a military base that hosted large fields of well-known cereals and stuff. I was told those fields were used to calibrate spy satellites, since the size and "color" of those fields are perfectly known. I guess they use those flat areas as well.
  • Wait, I'm confused.

    Did I just stumble onto a Bizarro-Slashdot where the Earth is flat and Intelligent Design is a sane, logical, evidence-supported theory?

    - RG>
  • > 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.'"

    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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