Forward-looking infrared

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Forward-looking infrared (FLIR) sensors produce images of objects from the heat energy they produce. The device may also do image processing, including such things as comparing the heat of the background to that of the target, which allows digital enhancement. These are also called thermal imagers. FLIRs use solid-state detectors, usually cooled well below the ambient temperature.

Historically, FLIRs operate in the far infrared spectrum, at wavelengths of 8-12 micrometers. This contrasts with night vision devices, or infrared film cameras, that can sense wavelengths no longer than 1-1.5 micrometers. Surprisingly sharp images can be generated, in night and fog, of objects whose internal temperature differs from that of their background. A tank engine, which has been off and cooling for several hours, is still "bright" in comparison to desert soil.

Medium infrared, with wavelengths between 3-5 micrometers, had required more expensive electronics and more intense cooling. These have much longer ranges due to these wavelengths being less absorbed by air than are the 8-12 micrometer wavelengths. Cost, however, had been a problem, but the new AN/ASQ-228, not cheap at $3.4 million each, apparently provides enough performance advantage to justify moving to this part of the spectrum.[1]

Military aircraft use

In military aircraft applications, separate devices with different resolution and field of view were used for navigation {NAVFLIR), weapons targeting (TFLIR) and laser designation. NAVFLIR is exceptionally important for low-altitude flight. Aircraft equipped with FLIR, often in combination with night vision goggles for the crew, include the B-52, MH-53 PAVE LOW, and MV-22 Osprey.

ATFLIR

Many aircraft need all three functions, and also may need lasers. For example, F-18 Hornet and F-18 Super Hornet previously carried AN/AAS-38 (Hornet) and AN/AAS-46 (Super Hornet) Targeting FLIRs, with separate AN/AAR-55 NAVFLIR.[2]

A new device, the AN/ASQ-228 ATFLIR, built by Raytheon with subsystems from BaE Systems, combines the three functions in one pod, and operates in the medium infrared, with 3.7-5.0 nanometer wavelengths. It is not only passive, but contains a laser designator It can also provide low-light television viewing in the visual range. [3] For the different applications, it can switch among 0.7°, 2.8° and 6.0° fields of view. While the exact performance is classified, the manufacturer's literature states it has over 40 nmi range, and can laser designate/measure ranges from altitudes greater than 50,000 feet.

When the various FLIR functions were in different pods, they each occupied a pylon or other hardpoint on the aircraft. Consolidating pods allows the aircraft to carry additional weapons on the hardpoints made available.

Military ground use

In the Gulf War, first-generation FLIR gave significant advances over previous night viewing systems, doing such things as showing a view, sufficient to hit it with the main gun, of a tank hiding behind a sand dune. A second-generation system improves the range and target acquisition speed. There are separate viewers for the tank commander and gunner, allowing the gunner to engage a target while the commander looks for the next. Optically, it can operate in 3 or 6 power for wide-angle target acquisition, and 13, 25, or 50 power for aiming.[4]

In the new Brigade Combat Teams, the Long-Range Advanced Scout Surveillance System {LRAS3), used for surveillance and tracking, either on a vehicle or a tripod mount, contains FLIR as well as a laser designator.

FLIR is used in the new Rocket Artillery Launch Spotter, which is a hybrid using electro-optical and acoustic MASINT sensors.

References