Bolivian Salt Flats Aid Spacecraft Calibration

PCOL writes: "Salar de Uyuni is a vast plain of white cemented salt in the mountains of Bolivia roughly 25 times the size of the Bonneville Salt Flats with a total elevation range of less than 80 centimeters making it the flattest place on earth. Beginning in 2002, Adrian Borsa, a geophysicist at the US Geological Survey in Pasadena, California, led the survey that resulted in precise GPS measurements of the salt flat, characterizing its elevation to an accuracy of 2.2 centimeters. "It's as if you're on a white ocean with no waves," says Borsa. "You see the horizon, the curvature of Earth. It's absolutely featureless." But what has been the salt flats attraction for scientists? The salt 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. Salar de Uyuni is also one of the few terrestrial locations where gravitational fields are able to play a major role in shaping local ( 100 km) topography with a land surface that has been shown to undulate in step with earth's local gravitational field creating faint mounds of some 40 centimeters in height over regions of slightly higher gravity, owing to high-density volcanic rocks kilometers below. After taking out the elevation variations that are due to gravity, Borsa is so far seeing a strange, regularly patterned checkerboard surface that could reflect the imprint of periodic pressures due to prevailing winds. Working out the forces that produce this pattern could be useful if similar phenomena are ever spotted on another planet, says Borsa. "Now we've got an analogue on Earth.""