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Infrared thermography is a procedure for creating images using infrared (IR) radiation instead of light. IR is invisible to the naked eye, but is emitted or reflected by any object or creature that gives off heat. Infrared thermography, also known simply as thermography, creates an image based on the heat patterns of the area in view. This has numerous technical and scientific applications, from military surveillance to astronomy. An image created by thermography is called a thermogram.
Infrared radiation is part of the electromagnetic spectrum, a wide range of harmless radiation that includes visible light, radio waves, and microwaves. The wavelength of the radiation determines its nature and position on the electromagnetic spectrum. Although the human eye can detect only a narrow range of this radiation, various technological devices can detect the rest of it. The wavelength of infrared radiation places it between microwaves and red light, just outside the visible spectrum. IR radiation that is near the visible range can be captured with special cameras for IR photography; infrared thermography can capture the IR radiation that is closer to microwaves, known as far infrared.
An object’s IR radiation is closely linked with its temperature. As a result, infrared thermography can detect subtle variations in the heat emitted by an object, creature, or person. As all objects emit some amount of heat, thermography allows an environment to be observed in its totality, even in the complete absence of light. A thermogram of a house, for example, might show exteriors outlined in blue, but interior heat and energy sources, including people, as red objects. These characteristics of thermography have multiple applications in a wide variety of fields and professions.
In medicine, for example, infrared thermography can aid the early diagnosis of disease by detecting the elevated heat levels caused by fever. Military personnel use thermography for surveillance and operations when ordinary light sources would be hazardous. Meteorologists can detect temperature changes that indicate storms and other rapidly changing weather patterns. Thermograms of buildings can reveal “hot spots,” allowing technicians to find problem areas in ventilation or electrical systems before they cause failures. Even archaeologists use thermography to locate buried structures that absorb or reflect heat differently than the surrounding terrain.
Astronomers have used infrared radiation for decades, as it can detect celestial bodies beyond the range of ordinary telescopes. Infrared thermography use for astronomy was initially limited, because the Earth’s atmosphere absorbs and deflects so much IR radiation. Orbiting space telescopes, however, can employ thermographic equipment without such limitations. This equipment must be cooled to prevent external heat sources from distorting the data. Thermograms have been used to observe distant planetary bodies and infant stars that have not yet begun to emit visible light.