What is the inband for Longwave infrared operation?

• A. 5-8 Micrometers
• B. 3-5 Micrometers
• C. 7.5-14 Micrometers
• D. 10-20 Micrometers

Answer: (C)

Longwave infrared imaging focuses on the wavelengths where objects at typical scene temperatures emit most strongly and where the atmosphere remains relatively transparent. The peak of thermal emission for objects near room temperature sits around 9–10 micrometers, and detectors used for LWIR—like microbolometers or HgCdTe sensors—are designed to be most sensitive in a window that covers roughly 7.5 to 14 micrometers. This range captures the strong thermal signal while minimizing loss due to atmospheric absorption, giving clear, usable images.

Ranges that lie in shorter wavelengths fall into the midwave infrared, where different targets and detectors are used and where the thermal signal is weaker for typical ambient-temperature scenes. Extending beyond 14 micrometers moves into wavelengths where the atmosphere absorbs more and detector efficiency drops, so those wavelengths aren’t the standard inband for LWIR operation. That’s why 7.5–14 micrometers is the best fit for longwave infrared imaging.