The Negative Ultraviolet Contrast of Airborne Objects

Aerial craft against the sky are visible in the ultraviolet (UV) range as dark objects. The properties of negative UV contrast differ from the properties of positive thermal contrast. The use of a UV channel in observation devices increases their detection and selection ca-pabilities. The paper analyses the influence of individual components of UV radiation on the signature of an airborne objects and presents the results of calculations of UV radiance and negative contrast depending on the object-observer distance for selected geographical locations and times of day and year as well as on the range of visibility. It was found that UV radiance mostly depends on the sun's elevation, while the contrast depends almost only on the range of visibility, i.e., aerosol’s type and density. A case of negative contrast in atmosphere was measured and the measured data are compared with calculations.