Satellite radar altimetry reveals spatial and temporal changes in water surface smoothness in the Salar de Uyuni, Bolivia

The Salar de Uyuni is a desert made of salt and is called the world’s largest natural mirror when it is covered with a thin layer of water. However, that statement has never been scientifically proven through research. The only evidence is from smartphone photographs taken along the border, as the interior area is not easily accessible during the wet season. Here, we present a methodology based on Radar Cross Section to measure surface smoothness using radar altimeter observations from Sentinel-3 satellites. The methodology was validated using ground-truth measurements collected during a unique field survey conducted in its interior while it was water-covered and coinciding with a satellite overpass. We show that the whole Salar de Uyuni is not a uniform mirror reflecting radar waves, as the smoothness at visible light wavelength would induce one to believe. Instead, the smoothness of the water surface evolves spatially and temporally. The whole Salar de Uyuni in Bolivia is not a uniform mirror-like surface in which anything above it is reflected specularly, instead the smoothness of the water surface evolves spatially and temporally, according to an analysis using radar altimeter observations from Sentinel-3 satellites.