a), b), and c) average normalized reflectance spectra of three different bright features (blue) and dark terrain nearby (red) for the examples shown in Figs. 7e, c, and a, respectively. Spectra of the bright features were averaged over a region of interest (ROI) of a few pixels defined inside the bright feature, avoiding its edges that are often affected by imperfect coregistration at the pixel scale. Spectra of the dark soil were averaged in a similar way over regions defined by avoiding all visible shadows in the image. All spectra were then normalized by their value of reflectance at 535.7 nm. d), e), and f) corresponding ratios between the average spectra of the bright feature and the average spectra of the dark soil (crosses) and linear fit through these points (dashed lines).