Infrared Signature

The term infrared signature is used by defense scientists and the military to describe the appearance of objects to infrared sensors. An infrared signature depends on many factors, including the shape and size of the object, temperature and emissivity, reflection of external sources (earthshine, sunshine, skyshine) from the object's surface, the background against which it is viewed 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.

Infrared stealth is an area of stealth technology aimed at reducing infrared signatures. This reduces a platform's susceptibility to infrared guided weapons and infrared surveillance sensors, and thus increases the platform's overall survivability. Infrared stealth is particularly applicable to military jets because of the detectable engines and plumes from non-stealth aircraft, but it also applies to military helicopters, warships, land vehicles and dismounted soldiers.

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.

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.