Forward looking infrared
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A forward looking infrared (FLIR) is a device that senses infrared radiation.
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.
Many FLIR systems use digital image processing to improve the image quality. FLIR 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.
FLIRs, such as the AN/AAQ-26, are often used in naval vessels, fixed-wing aircraft, helicopters, and armored fighting vehicles. In warfare, they have three large advantages. First, the imager itself is nearly impossible for the enemy to detect, as it detects energy that's already there, and doesn't have to send out any energy of its own. Second, it sees heat, which is hard to camouflage. Thirdly, FLIR systems can see through smoke, fog, haze, and other atmospheric obscurants better than a visible light camera can. However, it is hard to distinguish friend from foe when using the FLIR, which has led to friendly fire incidents.
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[edit] Origin of the term FLIR
The term "forward looking" is used to distinguish FLIR systems from sideways tracking infrared systems. Such systems were/are typically used on aircraft and satellites. They normally involve a 1D array of pixels which uses the motion of the aircraft or satellite to move the view of the 1D array across the ground to build up a 2D image over time. Such systems cannot be used for real time imaging, and must look perpendicular to the direction of travel. To some extent they have been made obsolete by the development of "forward looking" imaging systems.
[edit] Uses of FLIR
- Surveillance of people
- Watershed temperature monitoring and monitoring wild game habitats
- Detection of energy loss or insulation defects in buildings in order to reduce HVAC energy consumption
- Target acquisition and tracking by military aircraft
- Piloting of aircraft in low visibility (IFR) conditions
- Warning drivers about deer and other animals on the road
- Locating living beings (through smoke and walls) and pinpointing sources of ignition during firefighting operations
- Search and rescue operations for missing persons especially in wooded areas or water.
- Detecting leaks of natural gas and other gasses.
- Monitoring active volcanoes.
[edit] Cost
The cost of FLIR equipment has fallen dramatically. Older camera designs used rotating mirrors to scan the image to a small sensor. More modern cameras no longer use this method; the simplification helps reduce cost.
[edit] Privacy
In 2001, the United States Supreme Court decided that performing FLIR surveillance of private property without a search warrant by law enforcement violates the Fourth Amendment's protection from unreasonable searches and seizures. Kyllo v. United States, 533 U.S. 27 (2001) [1]
