Temperature as a quantitative indicator of internal energy of the bodies is a universal characteristic of objects and processes of the physical world, in which there is a continuous generation, conversion, transfer, stockpiling and use of energy in its various forms. Analysis of thermal processes (thermal fields, heat loss, etc.) allows you to get a variety of information about the state of objects and physical processes in nature, energy, construction, industry, etc.
Anybody with a temperature different from absolute zero is the source of infrared (thermal) radiation, discovered in 1800s by William Herschel. Direct relation between intensity of thermal radiation from a body and its temperature, based in the laws of thermal radiation Stefan-Boltzmann, Planck, Wines, allows to perform remote measurements of temperature by detecting thermal radiation. This feature of the technique called thermography (or thermal imaging).
Thermography means the method of analysis of spatial and temporal distribution of thermal energy (temperature) in physical objects usually accompanied by the construction of thermal images (thermograms).
Thermography as a part of diagnosis.
The principle of thermal diagnostics is analyzing and comparing temperature fields of basic reference standards to the tested object. Temperature anomalies are indicators of defects, and the magnitude of the temperature signals and their time behavior underlie quantitative estimates of certain parameters of the objects.
For thermal imaging method there is a general problem of technical diagnostics of defects: usually detected defects are in operating object, therefore, assess the possible damage is probabilistic.