Effect of atmospheric transmission and radiance on aircraft infrared signatures

This paper elaborates the role of atmosphere in determining infrared signatures of aircraft as perceived by a ground-based infrared detector, similar to the case of an infrared guided heat-seeking surface-to-air missile. The main objectives are to assess the effect of atmosphere on aircraft infrared signature and to evaluate infrared bands in which a conventional fighter-class aircraft is most susceptible to infrared guided missiles. Such an analysis Is of paramount importance for aircraft infrared signature management and aircraft mission planning. First, the lock-on range is derived as a function of aircraft, missile seeker, and atmospheric parameters. Thus, the role of atmospheric radiance and transmittance in determining aircraft signature level as perceived by the missile infrared seeker is brought out. The role of various atmospheric constituents in dictating infrared characteristics of the atmosphere is also discussed. The Berger's model is used for computing atmospheric/sky radiance and the Lowtran-7 model to compute atmospheric transmissivity. The infrared bands in which the aircraft signature is prominent are identified, and the variation of aircraft signature level and lock-on range with respect to a typical surface-to-air missile within these bands are analyzed and discussed for a representative case.