SWIR (Short Wave IR)
Short Wave IR (SWIR) is a subset of the infrared band in the electromagnetic spectrum, covering the wavelengths ranging from 1.4 to 3 microns. This wavelength is not visible to human eyes and as a result can often offer a better image than what is achievable with visible light imaging.
A number of manufacturers make SWIR imagers and FPAs (Focal Plane Arrays) that detect various ranges of the electromagnetic spectrum with various qualities. One type is InGaAs sensors which, unlike other sensor types, require no cryogenic cooling. They are sensitive to the 0.9 to 1.7 micron wavelengths, meaning that they detect both NIR (near infrared) and SWIR. InSb sensors are also available with a broad spectral response from 0.9 to 2.5 microns, and other cameras capable of sensing everything from 0.4 to 2.5 microns, covering the visible, NIR and SWIR regions with one sensor.
Advantages
No Illumination Needed
SWIR cameras are extremely sensitive to light, with individual pixels of the focal plane array able to capture and detect single photons. When combined with a phenomenon called night sky radiance, which emits up to 700% more illumination than starlight and is comprised mainly of SWIR wavelengths, SWIR cameras are able to see objects with a high level of detail, even on moonless and starless nights.
See Through Fog & Haze
The longer wavelengths of the SWIR spectrum are able to penetrate fog, smoke and other atmospheric conditions. As a result shortwave infrared cameras consistently provide superior images to their optical counterparts as they are able to see through these obstructions, making them particular useful in cities, marine and coastal protection.
Effective for Identification
Unlike thermal energy which is radiated, SWIR is a reflected energy like visible light, which makes it a viable technology for identification purposes, and the only such technology that can be effectively used at night without additional illumination. While images made from the SWIR wavelength are black and white, they have similar properties to visible light, such as reflection and contrast.
See Through Glass
Another advantage that SWIR has over thermal is its ability to see through glass. This not only allows SWIR cameras to look through most windows but also allows for more affordable glass lenses and housings to be used.
Disadvantages
Expensive
InGaAs and InSb focal plane arrays (FPAs) are more expensive to produce than standard silicon FPAs, which makes SWIR cameras more expensive than a standard visible/NIR camera.
ITAR Required
Because of its high performance, this technology is protected by the International Traffic in Arms Regulations, which places restrictions on where these products can be exported and who can purchase them.
Special Lenses Preferred
While the SWIR wavelength is able to use standard glass lenses, for maximum detail, specially developed lenses are recommended that are designed specifically to focus wavelengths in the 0.9−1.7 µm region.
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