Influence of temperature fluctuations on infrared limb radiance: a new simulation code

Airborne infrared limb-viewing detectors may be used as surveillance sensors in order to detect dim military targets. These systems' performances are limited by the inhomogeneous background in the sensor field of view which impacts strongly on target detection probability. SAMM-2 is an existing code able to model atmospheric structures and their impact on infrared limb-observed radiance. The AFRL background radiance code can be used to predict the radiance fluctuation as a result of a normalized temperature fluctuation, along a given line of sight (LOS). The existing code SIG was designed to compute the cluttered background which would be observed from a spaceborne sensor. However, this code was not able to compute accurate scenes as seen by an airborne sensor especially for LOS close to the horizon. Recently, we developed a new code called BRUTE3D adapted to airborne viewing conditions. This BRUTE3D code inputs a three-dimensional grid of temperature fluctuations and SAMM-2 transfer functions to synthesize an image of the atmospheric background clutter according to the sensor characteristics. This paper details the working principles of the code and presents some output results. The effects of the small-scale temperature fluctuations on infrared limb radiance as seen by an airborne sensor are highlighted.