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What is Infrared Thermography?

10/16/2013 8:17:56 AM | by Anonymous


Infrared thermography was discovered by Herschel, a British astronomer in 1800’s, when dispersing the sunlight using a prism. That is when Herschel accidentally found out that there is an invisible light on the outside of red light when there is an increase in the temperature of an object which is also known as infrared thermography.


Infrared thermography is a method or equipment that can detect the infrared energy emitted from object that converts it to temperature and displays image of temperature distribution. In order to be accurate, the method and equipment should be called differently. The equipment is called as thermograph infrared whereas the method should be called as infrared thermography.


Infrared thermography, thermal video or thermal imagings are examples of infrared imaging science. The thermography cameras can detect radiation in the infrared range of the electromagnetic spectrum roughly 9000-14000 nanometers or 9-14um. It can also produce images of that radiation called thermograms. The infrared radiation is emitted by all objects above the absolute zero according to the black body radiation law and the thermography makes it possible to see one’s environment with and without illumination.


The amount of radiation that is emitted by an object will increase with temperature therefore the thermography allows one to see variations in temperature. When viewed through a thermal imaging camera, the warm objects will stand out well against humans, cool background and other warm blooded animals become easily visible against the environment, night or day. As a result, the thermography is particularly useful to military and other users of surveillance cameras.


In the past, infrared thermography is used in the airport personnel and government to detect suspected swine flu cases during the 2009 pandemic. Firefighters also use thermography to see through smoke to localize the base of a fire and to find persons. As for the building construction technicians, they can see thermal signatures that indicate heat leaks in faulty thermal insulation and can use the results to improve efficiency of air conditioning and heating units. However, some physiological changes in human beings and other warm blooded animals which can also be monitored with thermal imaging during clinical diagnostics.


The operation and appearance of a modern thermographic camera is often similar to a camcorder. The live thermogram will reveal the temperature variations so clearly that a photograph is not necessary for analysis and a recording module is not always built-in.


The non-specialized charge coupled device and complementary metal oxide semiconductor have most of their spectral sensitivity in the visible light wavelength range. However, by utilizing the “trailing” area of their spectral sensitivity namely the part of infrared spectrum is called near-infrared. By using off the shelf CCTV camera, it is possible that under certain circumstances to obtain the true thermal images of objects with temperatures at about 280 degrees Celsius and higher.


The specialized thermal imagining cameras are used for focal plane arrays that respond to longer wavelengths from mid to long-wavelength infrared. The most common types are QWIP FPA, InGaAs and InSb. The newest technologies are used for low cost and uncool mircobolometers as FPA sensors. Their resolution is considerably lower than the optical cameras and mostly 320 x 240 pixels up to 640 x 512 or 160 x 120 for the most expensive models.


However, thermal imaging cameras are much more expensive than their visible spectrum counterparts and are higher end models as well as are often export restricted due to the military uses for this technology. Other older bolo meters or more sensitive models such as InSb require cryogenic cooling that is usually by a liquid nitrogen or miniature sterling cycle refrigerator.

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