Thermal imaging refers to the production of images by cameras that detect radiation in the infrared (IR) range of the electromagnetic spectrum. Infrared radiation has a wavelength longer than visible light, though shorter than that of microwaves, measuring approximately 900 to 14,000 nanometers.
Thermographic cameras produce images in a way similar to cameras that use visible light, except that visible light cameras capture wavelengths in the 450- to 750-nanometer range of the electromagnetic spectrum-wavelengths too short for thermal imaging equipment to register.
All objects emit infrared radiation, the amount of which is proportional to an object’s temperature. Thermography makes it possible to view objects by varying degrees of heat, with warmer objects rendered brighter than cooler objects.
Thermographic inspection is a form of nondestructive testing that is safe, non-intrusive and noncontact. It allows quick detection of subsurface defects a few millimeters under large surfaces. With passive thermographic inspection, features of interest are naturally at a higher or lower temperature than the background. With active thermographic inspection, an energy source is needed to produce a thermal contrast between the feature of interest and the background.