Daytime low light conditions such as overcast, dawn, and dusk pose a challenge for object discrimination in the reflective bands, where the majority of illumination comes from reflected solar light. In reduced illumination conditions, sensor signal-to-noise ratio can suffer, inhibiting range performance for recognizing and identifying objects of interest. This performance reduction is more apparent in the longer wavelengths where there is less solar light. Range performance models show a strong dependence on cloud type, thickness, and time of day across all wavebands. Through an experimental and theoretical analysis of a passive sensitivity and resolution matched testbed, we compare Vis (0.4-0.7μm), NIR (0.7-1μm), SWIR (1-1.7μm), and eSWIR (2-2.5μm) to assess the limiting cases in which reduced illumination inhibits range performance.

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Lindsey Wiley, Richard Cavanaugh, Joshua Follansbee, Derek Burrell, Robert Grimming, Rich Pimpinella, Jeff Voss, Orges Furxhi, and Ron Driggers, "Comparison of reflective band (Vis, NIR, SWIR, eSWIR) performance in daytime reduced illumination conditions," Proc. SPIE 12533, Infrared Imaging Systems: Design, Analysis, Modeling, and Testing XXXIV, 125330A (Presented at SPIE Defense + Commercial Sensing: May 03, 2023; Published: 14 June 2023); https://doi.org/10.1117/12.2663402.