UC San Diego

The salar de Uyuni in the Bolivian Andes is the largest salt flat on Earth, exhibiting less than 1 m of vertical relief over an area of 9000 km(2). We report on a kinematic Global Positioning System (GPS) survey of a 45-by-54 km area in the eastern salar, conducted in September 2002 to provide ground truth for the Ice Cloud and land Elevation Satellite (ICESat) mission. GPS post-processing included corrections for long-period GPS noise that significantly improved survey accuracy. We fit corrected GPS trajectories with 2-D Fourier basis functions, from which we created a digital elevation model (DEM) of the surface whose absolute accuracy we estimate to be at least 2.2 cm RMSE. With over two magnitudes better vertical resolution than the Shuttle Radar Topography Mission data, this DEM reveals decimetre-level topography that is completely absent in other topographic data sets. Longer wavelengths in the DEM correlate well with mapped gravity, suggesting a connection between broad-scale salar topography and the geoid similar to that seen over the oceans.