Thermography or thermal imaging, is the detecting and analyzing heat radiation from the surface of objects
Thermography employs a device like a camera or pulsed thermography (PT) device. These devices have a large number of infrared sensors capable of detecting and measuring minute temperature variations. Graphics produced by these devices depict changes in temperature, and can be downloaded to a computer for analysis and reporting.
Typically, these images can be easily recognized as a color spectrum image, from red (hot) to blue/black (cold).
NDT Thermography comes in two forms, passive and active.
In passive thermography, a camera is simply pointed at the target material or object, and from the resulting thermal image a temperature map is constructed.
Active thermography is performed by rapidly heating an object's surface using an external heat source and recording how the temperature changes over time. Variations in the cooling rate of the object reveal flaws.