Average value of variables (normalized reflectance at 0.55 μm of the selected wavelengths) in groups identified from the OVIRS global data analysis: (a) average spectrum of the only groups obtained at a 3σ confidence level, (b) average spectra of the two groups distinguishable at a 2.7σ confidence level, and (c) average spectra of the five groups that can be distinguished at a 2.0σ confidence level. The error bar corresponds to the standard deviation of the distribution of the spectra in each group and at each wavelength.