Correlations between 2.7 µm band center and the depths of 3.1 and 3.9 µm bands across all surface types. The 2.7 µm band center vs. (a) 3.1 µm band depth and (b) 3.9 µm band depth. The black, blue, and red scatter points represent the ST1, ST2, and ST3, respectively. The 3.1 and 3.9 µm band depths were calculated with the same Gaussian fit procedure. The error bars for ST1 denote the standard deviations of the selected ROIs. For ST2 and ST3, color shading indicates data density, and the semitransparent colored regions mark the approximate ranges after accounting for the standard deviations. The correlation coefficients between 2.7 µm band center and 3.1 and 3.9 µm band depths were noted.