A
forward looking infrared (FLIR) is the
North American English term for a camera that takes pictures using the
infrared portion of the
electromagnetic spectrum. Elsewhere in the
English speaking world, these are typically called
Thermal imagers or "
infrared cameras".
Since FLIRs use detection of
thermal energy to create the "picture" assembled for the
video output, they can be used to help
pilots and drivers steer their vehicles at night, and in
fog, or detect warm objects against a cold background when it is completely dark (such as a cloudy, moonless night). Note that the wavelength of infrared that FLIRs detects differs significantly from that of
Night vision, which operates in the visible light and near infrared ranges (0.4 to 1.0 micrometres).
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
micrometre and can see heat such as hot engine parts or human
body heat a few miles away, but longer distance viewing is made more difficult because the infra-red light is
absorbed,
scattered and
refracted by the air and water vapor. Some long-wave FLIRs require their detector to be cryogenically cooled, although moderately sensitive FLIRs are produced that do not require cryogenic cooling.
Cameras which operate in the 3 to 5
micrometre 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.
