Infrared visibility and infrared visibility range: practical significance and a measurement method

The article presents new physical quantities (infrared visibility and infrared visibility range) while showing their relevance and demand for their measurement. The author reveals their physical meaning, provides calculation formulas, and proves their practical significance. The presented formulas are obtained by transforming the thermal image of an object into its equivalent thermal geometric model. The numerical values of the infrared visibility index are shown to vary for different real objects within a wide range: from zero for thermally non-contrast objects to values of several units for high-contrast objects, i.e., within the range of 0.5-2.5. The formula for infrared visibility range is derived in two ways: according to the Beer-Bouguer-Lambert law and Fechner's law used in sensory perception theory. A detailed description and a procedure for measuring the specified physical quantities are presented, examples are given, and the measurement uncertainty is estimated. The introduced quantities are designed to ensure uniform assessment of thermal protection in various man-made and biological objects and provide a means to develop preventive measures for their thermal protection during entry into service.