Scaled laboratory spectra for three different salts (gray) linearly combined with a synthetic spectrum (SS, black) that simulates the composition of Umbriel’s regolith, composed of a particulate mixture of crystalline H₂O ice (0.3 and 20 μm grain sizes, 0.8 and 53.6%, respectively), amorphous C (8 μm grain size, 27.5%), and crystalline CO₂ ice (10 μm grain size, 18.1%). Spectra have been offset vertically for clarity. The range in band centers for Umbriel’s 2.14 μm, 2.2 μm, 2.22 μm, and 2.24 μm bands (Tables A2–A5) is highlighted by the purple, blue, green, and red zones, respectively (shown in Figures 3 and 4). Additional putative features in the Umbriel spectra that may indicate the presence of NH₃, salts, and organics are highlighted by pairs of dotted lines spanning 1.583–1.597, 1.622–1.637, and 1.691–1.731 μm (shown in Figure 6). The spectra shown in Panel I are NH₄ carbonate (80 K) scaled by a factor of 0.012 (1a) and combined with spectrum SS (1b); NH₄ carbonate (80 K) scaled by a factor of 0.007 (2a) and combined with spectrum SS (2b). The spectra shown in Panel II are NH₄ chloride (90 K) scaled by a factor of 0.004 (3a) and combined with spectrum SS (3b); NH₄ chloride (90 K) scaled by a factor of 0.002 (4a) and combined with spectrum SS (4b). The spectra shown in Panel III are thermonatrite (93 K) scaled by a factor of 0.016 (5a) and combined with spectrum SS (5b); thermonatrite (93 K) scaled by a factor of 0.008 (6a) and combined with spectrum SS (6b). Unscaled versions of these laboratory spectra are shown in Figures 4 and 6.