Figure 4

Dune spectral distance. Global spectral distance map. We show the distance in {1.08 μm, 1.28 μm, 1.6 μm, 2 μm, 2.8 μm, 5 μm} vector space from a pixel’s atmospherically corrected and normalized albedo to the average value for the dunes in Aztlan. The base map is the empirically corrected mosaic from Figure 3. Due to systematic errors in the atmospheric correction, the map should still be considered in context with the observation geometry. Broadly, the distances map closely to albedo variations — the VIMS ‘dark blue’ spectral unit (which includes the Sinlap parabola and the Huygens Landing Site, for instance) shows a small distance (dark) from the sand spectrum despite its distinct spectral signature [19,20].