NIR (Near-Infrared) Imaging (Fog/Haze Filter)
Near Infrared (NIR) is a subset of the infrared band of the electromagnetic spectrum, covering the wavelengths ranging from 0.7 to 1.4 microns. This wavelength is just outside the range of what humans can see and can sometimes offers clearer details than what is achievable with visible light imaging.
NIR is very close to human vision but removes the color wavelengths, which results in most objects looking very similar to an image that has been converted to black and white. One exception is trees and plants, which are highly reflective in the NIR wavelength and thus appear much brighter than they do in color. That difference in reflectivity of certain objects, in combination with reduced atmospheric haze and distortion in the NIR wavelength, means that detail and visibility are often improved at long ranges, as shown in the comparison image below:
See Through Haze & Smoke
The longer wavelengths of the NIR spectrum are able to penetrate haze, light fog, smoke and other atmospheric conditions better than visible light. For long-distance imaging, this often results in a sharper, less distorted image with better contrast than what can be seen with visible light.
Effective for Identification
Unlike thermal energy which displays objects quite differently from visual perception, NIR is a reflected energy that behaves similar to visible light, which means that it can see things like printed information on signs, vehicles and vessels that thermal imaging usually cannot. Faces, clothing and many other objects will also look more natural and recognizable than they do in thermal.
Takes Advantage of Existing Optics
The premium glass lenses that we use for our HD visible imaging are designed with NIR in mind, so an additional lens and sensor are not needed. With a simple preset call, a motorized IR filter is applied and the sensor switches to a special NIR mode, allowing the operator to quickly switch back-and-forth between the two imaging methods.
Disadvantages of NIR Imaging
While imaging in NIR has many great advantages, it’s not a perfect or complete solution for every situation. Here are some limitations you should be aware of with NIR imaging technology.
Every color is a specific wavelength of light. Blues are around 400nm, greens are around 520nm, etc. Since NIR detects the light between 700nm to 1400nm, we’re seeing information beyond the wavelengths that make up color, so the image is represented in greyscale values.
Requires Illumination at Night
NIR is a reflected energy like visible light, which means that an NIR light source is required to create an image. During the day there is plenty of IR light from the sun, but at night, an IR light source is needed to illuminate an area. IR light sources have the advantage of being invisible to the human eye, but they are not a truly passive surveillance option.
Most cameras that use NIR at night utilize IR LEDs for illumination, which are limited in range, usually no more than 500m. Infiniti has developed a laser technology that focuses its NIR illumination as the user zooms, extending the possible illumination range to be as far as 5km. For more information, see our ZLID Illumination page.
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