A computer model that takes into account the effect of aerodynamic
and solar heating, sky irradiation, and radiative cooling on infrared
emission from missile noses is presented. The heat transfer equation
was solved with numerical techniques both in the steady-state (constant
speed and altitude flight of cruise missiles) and in the nonstationary regime
(quickly variable speed and altitude of short to medium range ballistic
missiles) to give the temperature distribution on the skin surface. The
corresponding head-on absolute infrared emission in the 3 to 5 ?m and
8 to 12 ?m spectral bands was computed as a function of time of flight
and missile altitude. Results show a strong dependence of temperature
and radiant intensity distributions on thermal and geometrical properties
of the skin material, on the character of the aerodynamic flow (laminar or
turbulent boundary layer), and on the physical characteristics of the atmosphere.
By varying these parameters into reasonable ranges, infrared
emissions spanning over more than an order of magnitude were obtained.
The comparison with data corresponding to a skin uniformly kept at the
boundary layer effective temperature showed that huge overestimates of
the infrared emission can be found when the target is flying at high speed
and high altitude. By computing the ratio of the in-band total radiant
intensity in the 3 to 5 ?m and 8 to 12 ?m spectral regions, the relative
merits of these regions for the detection of a given target are given as a
function of missile altitude.