vs. active thermography All objects above the absolute zero temperature (0 K) emit infrared radiation. Hence, an excellent way to measure thermal variations is to use an infrared vision device, usually a focal plane array (FPA) infrared camera capable of detecting radiation in the mid (3 to 5 μm) and long (7 to 14 μm) wave infrared bands, denoted as MWIR and LWIR, corresponding to two of the high transmittance infrared windows. Abnormal temperature profiles at the surface of an object are an indication of a potential problem. In passive thermography, the features of interest are naturally at a higher or lower temperature than the background. Passive thermography has many applications such as surveillance of people on a scene and medical diagnosis (specifically thermology). In active thermography, an energy source is required to produce a thermal contrast between the feature of interest and the background. The active approach is necessary in many cases given that the inspected parts are usually in equilibrium with the surroundings. Given the super-linearities of the black-body radiation, active thermography can also be used to enhance the resolution of imaging systems beyond their diffraction limit or to achieve super-resolution microscopy. Advantages It shows a visual picture so temperatures over a large area can be compared. It is capable of catching moving targets in real time. It is able to find deterioration, i.e., higher temperature components prior to their failure. It can be used to measure or observe in areas inaccessible or hazardous for other methods. It is a non-destructive test method. It can be used to find defects in shafts, pipes, and other metal or plastic parts. It can be used to detect objects in dark areas. It has some medical application, essentially in physiotherapy. Limitations and disadvantages There are various cameras cheaper and more expensive. Quality cameras often have a high price range (often US$3,000 or more) due to the expense of the larger pixel array (state of the art 1280 x 1024), while less expensive models (with pixel arrays of 40x40 up to 160x120 pixels) are also available. Fewer pixels reduce the image quality making it more difficult to distinguish proximate targets within the same field of view. There is also a difference in refresh rate. Some cameras may only have a refreshing value of 5 –15 Hz, other (e.g. FLIR X8500sc) 180 Hz or even more in no full window mode. Also the