Infrared signature
Infrared signature, as used by
and the waveband of the detecting sensor. As such there is no all-encompassing definition of infrared signature nor any trivial means of measuring it. For example, the infrared signature of a truck viewed against a field will vary significantly with changing weather, time of day and engine loading.Two fairly successful examples of defining the infrared signature of an object are the apparent temperature difference at the sensor and the contrast radiant intensity (CRI) definitions.
Apparent temperature difference
The apparent temperature difference method of defining infrared signature gives the physical temperature difference (e.g. in
Contrast radiant intensity
The contrast radiant intensity method of defining infrared signature is to take the difference in average radiance of the object and that of the immediate background and multiply this by the projected area of the object. Again the CRI value will depend on many factors.
Commercial software
In the design phase, it is often desirable to employ a computer to predict what the infrared signature will be before fabricating an actual object. Many iterations of this prediction process can be performed in a short time at low cost, whereas use of a measurement range is often time-consuming, expensive and error-prone.
A number of software houses have built infrared signature prediction software packages. These generally require a CAD model of interest plus a large set of parameters to describe a specific thermal environment and the internal temperatures of the platform and thermal properties of the construction materials. The software then solves a set of thermal equations across the boundaries and for electromagnetic propagation in a specified infrared waveband. The primary output is a measure of infrared signature, though usually surface temperatures can be given (since this usually has to be calculated to obtain the infrared signature prediction) and also visual representations of how the scene may appear to various imaging infrared detectors.
Infrared signature prediction models are very difficult to validate except for simple cases because of the difficulty in modelling a complex environment. Both sensitivity analysis of this type of software and experimental measurements has shown that small variations in weather can have a significant impact on the results. As such, there are limitations on what can be achieved from modelling the infrared problem, and sometimes experimentation is necessary to achieve accurate knowledge of the nature of an object's physical existence in the infrared wavebands.
Infrared stealth
A military aim in studying infrared signatures is to understand the likely infrared signature of threats (and develop the equipment required to detect them) and to reduce the infrared signature of their own assets to threat sensors. In practice this might mean equipping a warship with sensors to detect the exhaust plumes of incoming anti-ship missiles while also having an infrared signature below the detection threshold of the infrared sensor guiding the missile.
An exhaust plume contributes a significant infrared signature. One means to reduce IR signature is to have a non-circular
Ground combat includes the use of both active and passive infrared sensors and so the
See also
- Infrared
- Electromagnetic modeling
- Radar cross section
- Infrared detector
- Infrared countermeasures
- Survivability
References
- ^ The Handbook Of The SAS And Elite Forces. How The Professionals Fight And Win. Edited by Jon E. Lewis. p.330-Tactics And Techniques, Personal Skills And Techniques. Robinson Publishing Ltd 1997. ISBN 1-85487-675-9
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- ^ Mahulikar, S.P., Sane, S.K., Gaitonde, U.N., & Marathe A.G.: (2001) "Numerical studies of infrared signature levels of complete aircraft", Aeronautical Journal, v. 105(1046), pp. 185-192.
- ^ Mahulikar, S.P., Potnuru, S.K., & Rao, G.A.: (2009) Study of sunshine, skyshine, and earthshine for aircraft infrared detection, Journal of Optics A: Pure & Applied Optics, v. 11(4), no. 045703.
- ^ Rao, G.A., & Mahulikar, S.P.: (2005) "Effect of atmospheric transmission and radiance on aircraft infrared signatures", AIAA Journal of Aircraft, v. 42(4), pp. 1046-1054.
- ^ Mahulikar, S.P., Sonawane, H.R., & Rao, G.A.: (2007) "Infrared signature studies of aerospace vehicles", Progress in Aerospace Sciences, v. 43(7-8), pp. 218-245.
- ^ Rao, G.A., & Mahulikar, S.P.: (2005) "New criterion for aircraft susceptibility to infrared homing missiles", Aerospace Science & Technology, v. 9(8), pp. 701-712.
- ^ Mahulikar, S.P., Kolhe, P.S., & Rao, G.A.: (2005) "Skin temperature prediction of aircraft rear fuselage with multi-mode thermal model", AIAA Journal of Thermophysics & Heat Transfer, v. 19(1), pp. 114-124.
- ^ Mahulikar, S.P., Rao, G.A., Sane, S.K., & Marathe, A.G.: (2005) "Aircraft plume infrared signature in nonafterburning mode", AIAA Journal of Thermophysics & Heat Transfer, v. 19(3), pp. 413-415.
- ^ Mahulikar, S.P., Prasad, H.S.S., & Potnuru, S.K.: (2008) "Infrared signature suppression of helicopter engine duct based on `conceal and camouflage`", AIAA Journal of Propulsion & Power, v. 24(3), pp. 613-618.
- ^ [1] Optical Warfare - The New Frontier
- ^ GAO-10-669R Warfighter Support