The OR-5008/AA Forward Looking Infra-Red (FLIR) is a derivative of Texas Instruments OR-89/AA (Jane's Information Group, 1993). The FLIR system enables the CP-140 to identify objects in complete darkness by analyzing their salient heat characteristics as identified by the infra-red (IR) emissions that it detects. IR radiation is focused by lenses in a lens switching assembly onto a set of rotating scan mirrors. The radiation is then reflected to a multi-element IR detector array, where it is converted to video signals. These are then amplified sufficiently to modulate the light output of light emitters in the light-emitter array. This light is then reflected by a second set of rotating scan mirrors, passed through a prism and projected onto a television camera. The video signal is finally amplified again and sent to the operator's display .This imaging sensor has a useful range extending anywhere from 12 to 20 DM for ships, 12 to 14 DM for surface subs, 6 to 8 DM for a submarine snorkel, and 2 to 4 DM for a submarine periscope, depending on the observing conditions, especially the sea state. It can easily detect rafts, bodies and dinghies in a SAR mission. A prime use of FLIR is intelligence gathering, particularly in post-mission analysis, since an over-flight at 250 km/h does not allow for immediate recognition of all possible details. In fact there are special courses for FLIR intelligence gathering.
In daylight conditions, it is most useful when smoke, haze or light fog are present. This IR detector is located in a retractable turret in the lower portion of the radome. The sensing element is stabilized with gimbals to turn through the complete 360° in azimuth and from +5° to -80° in elevation angle. This provides for a 5° look-up capability. The FLIR is controlled primarily by the NASO 1 station but, through computer control, can be displayed by the pilot, TACNAV, NAVCOM and NASO 2 operator. In addition, the pilot can exercise limited control through his or her keyset.
The FLIR detects wavelengths in the 8-14 mm range coming from objects emitting blackbody radiation characteristic of their temperature. Glare is also much less of a problem for the FLIR than for cameras operating in the visible spectrum because the sun emits much less in the IR region than in the visible. The FLIR can be automated and fused (ie integrated) with other sensors that operate over the same range (e.g., the search radar). At present, a template is placed directly on the FLIR screen by a human operator to manually estimate target sizes given the relevant range information obtained verbally from the radar operator.
There exist commercial off-the-shelf (COTS) frame-grabbers that can digitize FLIR video data for further processing. Any target recognition algorithm developed will assume that such digitized information is available. The attitude of the target can also be judged and targets can be additionally classified according to top, side and forward cross-section measurements when the angular size information of the FLIR is fused with radar range measurements. Of course, the fusion function's platform data base (PDB) must have relevant attribute information included for every possible entry.
There are many civilian applications, such as sea ice surveillance and the detection of oil spills and water pollution, since all these materials distinguish themselves most readily in the IR by absorbing and radiating heat in a vastly different way than the ambient water. As far as identification is concerned, the FLIR is indispensable for night patrols but otherwise is used only at lower altitudes when visual observations are rendered difficult by the sea state. The FLIR is also essential for the electro-magnetically silent missions previously identified.
The FLIR is an extremely hard sensor to model and any results of FLIR classifiers will have to rely on unclassified imagery, which has been procured for this purpose from the China Lake Naval Air Warfare Center (NAWC) of the US Navy through Dr. Sklansky of the University of California at Irvine.
Reference:1) Information Fusion Concepts For Airborne Maritime Surveillance and C2 Operations by P. Valin ,É. Bossé and A. Jouan dated May 2006. Document #P525407