In Passive Thermography, the features of interest are naturally at a higher or lower temperature than the background. Any object above the absolute zero temperature will emit IR radiation, which corresponds to the band of the between 0.74 and 1000 μm. Hence, an excellent way to measure thermal variations is to use an IR radiometer, usually a focal plane array (FPA) camera capable of detecting radiation in the mid (3 to 5 μm) or long (8 to 14 μm) wave infrared bands, denoted as MWIR and LWIR, respectively, corresponding to two of the high transmittance atmospheric windows as shown in Figure 1. Passive Thermography has many applications e.g. surveillance of people on a scene, medical.
In Active Thermography an energy source is required to produce a thermal contrast between the feature of interest and the background, e.g. a specimen with internal flaws. The active approach is adopted in many cases given that the inspected parts are usually in equilibrium with the surroundings.
Last update: Wednesday, November 21, 2007
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