Modeling the topography of the salar de Uyuni, Bolivia, as an equipotential surface of Earth's gravity field

Abstract

[1] The salar de Uyuni is a massive dry salt lake that lies at the lowest point of an internal drainage basin in the Bolivian Altiplano. A kinematic GPS survey of the salar in September 2002 found a topographic range of only 80 cm over a 54 Â 45 km area and subtle surface features that appeared to correlate with mapped gravity. In order to confirm the correlation between topography and gravity/geopotential, we use local gravity measurements and the EGM96 global geopotential model to construct a centimeter-level equipotential surface corresponding to the elevation of the salar. Our comparison of GPS survey elevations with the equipotential surface estimate shows that 63% of the variance of the GPS elevations can be explained by equipotential surface undulations (and long-wavelength error) in the EGM96 model alone, with an additional 30% explained by the shorter-wavelength equipotential surface derived from local gravity. In order to establish a physical connection between topography and the geopotential, we also develop and test a simple surface process model that redistributes salt via the dissolution, transport, and redeposition of salt by precipitated water. Forcing within the model pushes the system to evolve toward constant water depth, with the salt surface approximating the shape of the local equipotential surface. Since the model removes almost all topographic relief with respect to the equipotential surface within a matter of decades, it appears that observed ($5 cm amplitude, $5 km wavelength) residual topography is actively maintained by a process independent of gravity-driven fluid flow.

A Terrestrial Validation of ICESat Elevation Measurements and Implications for Global Reanalyses

“…To correct for height changes due to fuel consumption, we measured the vehicle antenna height before and after each survey and linearly interpolated the change to each GPS epoch based on distance driven. Borsa et al [8] provide details of the survey methodology and data postprocessing.…”

“…Using the methodology in [7], we corrected the elevation profiles using constraints provided by crossover points in the survey grid and by the known elevations of the fixed GPS sites. Using the corrected elevation profiles, we generated WGS84-referenced DEMs of the survey region, which fit the underlying GPS elevations at the subcentimeter level [8].…”