The Minimum Resolvable Temperature Difference (MRTD) is a classic performance parameter, used by manufacturers of thermal imaging systems (FLIR's) in the characterization and final testing of such devices. The Johnson criterion  relates the MRTD to practical characteristics, such as the ability of the FLIR to resolve objects, as function of distance. However, the MRTD measurement suffers from several drawbacks,e.g. i) it is subjective, ii) it fails to account for complex real life situations, such as background and foreground clutter, object shape and non-uniformities of temperature and emissivity. This paper describes a new type of transparency which has been developed to simulate real infrared scenes. The transparency consists of a half-tone mesh of variable size holes which, when placed in front of a blackbody, simulates a two dimensional radiant emittance pattern. The pattern itself can be generated from a thermal image of any real object as seen by a high performance FLIR, from an artificially computer generated image, or from a combination of the two. Examples of thermoscenes and measurements of radiation distribution over a simple pattern are shown. Potential applications of the thermoscenes are also discussed.