Thanks. You sent me down a small rabbit hole.
Remainder of this post excerpted from a journal paper on IR pedestrian detection:
Objects generally emit infrared radiation across a spectrum of wavelengths, but only a specific region of the spectrum is of interest because sensors are usually designed only to collect radiation within a specific bandwidth. As a result, the infrared band is often subdivided into smaller sections.
The International Commission on Illumination (CIE) recommended the division of infrared radiation into three bands namely, IR-A that ranges from 700 nm to 1400 nm (0.7–1.4 μm), IR-B that ranges from 1400 nm to 3000 nm (1.4–3 μm) and IR-C that ranges from 3000 nm to 1 mm (3–1000 μm). A commonly used sub-division scheme can be given as follows: Near-infrared (NIR, IR-A DIN): This is of 0.7–1.0 μm in wavelength, defined by the water absorption, and commonly used in fiber optic telecommunication because of low attenuation losses in the SiO2 glass (silica) medium. Image intensifiers are sensitive to this area of the spectrum. Examples include night vision devices such as night vision camera.
Short-wavelength infrared (SWIR, IR-B DIN): This is of 13 μm. Water absorption increases significantly at 1450 nm. The 1530–1560 nm range is the dominant spectral region for long-distance telecommunications.
Mid-wavelength infrared (MWIR, IR-C DIN) or Intermediate Infrared (IIR): It is of 3–5 μm. In guided missile technology the 3–5 μm portion of this band is the atmospheric window in which the homing heads of passive IR ‘heat seeking’ missiles are designed to work, homing on to the IR signature of the target aircraft, typically the jet engine exhaust plume.
Long-wavelength infrared (LWIR, IR-C DIN): This infrared radiation band is of 8–14 μm. This is the “thermal imaging” region in which sensors can obtain a completely passive picture of the outside world based on thermal emissions only and require no external light or thermal source such as the sun, moon or infrared illuminator. Forward-looking infrared (FLIR) systems use this area of the spectrum. Sometimes it is also called “far infrared” Very Long-wave infrared (VLWIR): This is of 14–1000 μm. NIR and SWIR is sometimes called “reflected infrared” while MWIR and LWIR is sometimes referred to as “thermal infrared”. Now, we can summarize the wavelength ranges of different infrared spectrums as in Table 1.
Table 1. Wavelength range for different spectrums.
||0.4–0.7 μm (micro meter/micron)
|Near infrared (NIR)
||0.7–1.0 μm (micro meter/micron)
|Short-wave infrared (SWIR)
||1–3 μm (micro meter/micron)
|Mid wave infrared (MWIR)
||3–5 μm (micro meter/micron)
|Long wave infrared (LWIR)
||8–14 μm (micro meter/micron)
|Very long wave infrared (VLWIR)