Which wavelength range between midwave and longwave is unsuitable for infrared cameras due to humidity?

• A. 1-3 Micrometers
• B. 4-6 Micrometers
• C. 5-8 Micrometers
• D. 9-12 Micrometers

Answer: (C)

Humidity affects infrared transmission by water‑vapor absorption. In the mid-to-longwave region, water vapor has strong absorption features around 6–7 micrometers. The 5–8 μm range sits right in those absorption bands, so infrared light in that band is heavily attenuated in humid air. That makes imaging in this range unreliable, with poor contrast and low signal. Infrared cameras work best in atmospheric transmission windows, like roughly 3–5 μm (midwave) and 8–12 μm (longwave), where humidity has less impact. The 5–8 μm range is therefore unsuitable due to the humidity-related absorption in that band.