Comparison of empirical and predicted UV aircraft signatures

Abstract

In light of the potential threat to aircraft from missiles using Ultra Violet (UV) wavebands, it is important to understand the signature of an aircraft and how this can be predicted. This study compares empirical UV signature data to modelled data from CAMouflage Electro-Optical SIMulation (CAMEOSIM) to determine how well the contrast between the object and the background in the scene can be predicted. CAMEOSIM uses the standard MODerate resolution atmospheric TRANsmission (MODTRAN) model from Spectral Sciences (and the US Air Force) to estimate the radiative transfer through the atmosphere. Both MODTRAN and CAMEOSIM are well validated in visible and infrared radiative transfer. Work, including by Smith [1] has shown that MODTRAN can accurately predict UV radiative transfer through the atmosphere. Unfortunately, the work so far has concentrated on bulk transfer to describe the sky background in the UV. The aircraft scene is typically a negative contrast ‘hole’ in a positive sky background. Importantly, path-topath scattering is a key consideration in this scene since it is this that will tend to blur the edges of an object and reduce the contrast associated with it. MODTRAN, and therefore CAMEOSIM are not designed to work well for this particular scene so developed understanding of the limitations through testing is required. It was determined that prediction was possible up to ranges of less than 5km. The local visibility (in km) was required for this prediction but more accurate descriptions of the atmosphere were not.