Fig. 3: Near-infrared observations for polar regions.

(Left) Normalized NIRS3 reflectance spectra of the polar regions compared with the standard reference spectrum outside of the polar regions. The spectra are normalized at 2.5 µm. The error bars are indicative of the standard deviation amongst the spectra used to compute the average region of interest (black) spectrum and average standard reference spectrum (red). (Middle) Detail of the 2.72-µm feature regions. We show the continuum removed band. The continuum is removed using 2.6 µm and 2.9 µm as anchor points⁶⁷. The error bars are indicative of the standard deviation amongst the spectra used to compute the average region of interest (black) spectrum and average standard reference spectrum (red). (Right) Histogram distribution of the band depth for each day’s observation. All spectra in the day (red), spectra of the region of interest (black). The vertical dashed lines represent the average value of each distribution. a North pole (photometrically corrected data). b Otohime Facet A (non-photometrically corrected data). c Otohime Facet B (photometrically corrected data). d Otohime Facet C (photometrically corrected data).