Design
There are two basic ranges of infrared; long-wave infrared and medium-wave infrared. The long-wave infrared (LWIR) cameras, sometimes called "far infrared", operate at 8 to 12 μm and can see heat sources, such as hot engine parts or human body heat, a few miles away, but longer-distance viewing is made more difficult because the infrared light is absorbed, scattered, and refracted by the air and water vapor. Some long-wave cameras require their detector to be cryogenically cooled, typically for several minutes before use, although moderately sensitive infrared cameras are produced that do not require cryogenic cooling. Many thermal imagers including some forward looking infrared cameras are uncooled such as some LWIR Enhanced Vision Systems (EVS).
Cameras which operate in the 3 to 5 μm range are called medium-wave infrared (MWIR) and can see almost as well, as those frequencies suffer less from water-vapor absorption, but generally require a more expensive sensor array and cryogenic cooling.
Many camera systems use digital image processing to improve the image quality. infrared imaging sensor arrays often have wildly inconsistent sensitivities from pixel to pixel, due to limitations in the manufacturing process. To remedy this, the response of each pixel is measured at the factory, and a transform, most often linear, maps the measured input signal to an output level.
Some companies offer advanced "fusion" technologies that blend a visible-spectrum image with an infrared-spectrum image to produce better results than a single-spectrum image alone.
Read more about this topic: Forward Looking Infrared
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