Techniques and errors for apparent differential temperature calculations

There are several techniques for calculating apparent target-to-background differential temperatures, or apparent delta T. Apparent differential temperatures are equivalent blackbody differential temperatures that represent a target-to-background contrast with degradation due to atmospheric effects. Apparent delta T depends on a number of parameters including source emission characteristics and atmospheric transmission characteristics. Techniques for calculating apparent delta T range from broadband temperature and transmission calculations to spectral transcendental equations. Various techniques for calculating apparent delta T are reviewed in this paper. Six calculations are described and applied to four example scenarios. The four scenarios include longwave and midwave bands with humid summer and dry winter climates. Six apparent delta T's are plotted as a function of range for these scenarios. The techniques are compared and contrasted and descriptions of their corresponding errors are provided.