Today's Applications
The first patent for a total radiation thermometer was granted in 1901. The instrument used a thermoelectric sensor; it had an electrical output signal and was capable of unattended operation. In 1931, the first commercially-available total radiation thermometers were introduced. These devices were widely used throughout industry to record and control industrial processes. They are still used today, but mainly used for low temperature applications.
  The first modern radiation thermometers were not available until after the second World War. Originally developed for military use, lead sulfide photodetectors were the first infrared quantum detectors to be widely used in industrial radiation thermometry. Other types of quantum detectors also have been developed for military applications and are now widely applied in industrial radiation thermometry. Many infrared radiation thermometers use thermopile detectors sensitive to a broad radiation spectrum and are extensively used in process control instrumentation.

Figure1-6:Optics For Missile Guidance

  Infrared thermometers currently are being used in a wide range of industrial and laboratory temperature control applications. By using non-contact temperature sensors, objects that are difficult to reach due to extreme environmental conditions can be monitored. They can also be used for products that cannot be contaminated by a contact sensor, such as in the glass, chemical, pharmaceutical, and food industries. Non-contact sensors can be used when materials are hot, moving, or inaccessible, or when materials cannot be damaged, scratched, or torn by a contact thermometer.
  Typical industries in which non-contact sensors are used include utilities, chemical processing, pharmaceutical, automotive, food processing, plastics, medical, glass, pulp and paper, construction materials, and metals. Industrially, they are used in manufacturing, quality control, and maintenance and have helped companies increase productivity, reduce energy consumption, and improve product quality.
  Some applications of radiation thermometry include the heat treating, forming, tempering, and annealing of glass; the casting, rolling, forging, and heat treating of metals; quality control in the food and pulp and paper industry; the extrusion, lamination, and drying of plastics, paper, and rubber; and in the curing process of resins, adhesives, and paints.
  Non-contact temperature sensors have been used and will continue to be valuable for research in military, medical, industrial, meteorological, ecological, forestry, agriculture, and chemical applications.
  Weather satellites use infrared imaging devices to map cloud patterns and provide the imagery seen in many weather reports. Radiation thermometry can reveal the temperature of the earth's surface even through cloud cover.
  Infrared imaging devices also are used for thermography, or thermal imaging. In the practice of medicine, for example, thermography has been used for the early detection of breast cancer and for the location of the cause of circulatory deficiencies. In most of these applications, the underlying principle is that pathology produces local heating and inflammation which can be found with an infrared imager. Other diagnostic applications of infrared thermography range from back problems to sinus obstructions.
  Edge burning forest fires have been located using airborne infrared imagers. Typically, the longer wavelengths of the emitted infrared radiation penetrate the smoke better than the visible wavelengths, so the edges of the fire are better delineated.
  On the research front, one sophisticated infrared thermometry application is in the study of faults in metals, composites, and at coating interfaces. This technique is known as pulsed video thermography. A composite material consisting of a carbon-fiber skin bonded to an aluminum honeycomb is subjected to pulses of heat from a xenon flash tube. Infrared cameras record a frame-by-frame sequence of heat diffusion through the object, which is displayed on screen. Defects show up as deviations in the expected patterns for the material being tested.
  Among the military applications of radiation thermometry are night-vision and the "heat-seeking" missile. In the latter case, the operator simply launches the missile in the general direction of the target. On-board detectors enable the missile to locate the target by tracking the heat back to the source. The most widely known military infrared missile applications are the Sidewinder air-to-air missile and a satellite-borne intercontinental ballistic missile (ICBM) detection system.
  Both rely on detecting the infrared signature of an emission plume or very hot exhaust engine. The Sidewinder missile guidance system is shown schematically in Figure 1-5. A special infrared dome protects the optical system inside. The optical system consists of a primary and secondary mirror and a set of correction lenses to cause an image to focus onto a special reticle. All the light from the reticle is focused onto a detector (Figure 1-6). The reticle can modulate the radiation to distinguish between clouds and provide directional information.
  Portable surface-to-air missiles, SAMs, are effective defense units that guide themselves to a target by detecting and tracking the heat emitted by an aircraft, particularly the engine exhaust.

	References and Further Reading
	Album of Science, The 19th Century, Pearce L. Williams, Charles Scribner's Sons, 1978.
	Asimov's Chronology of Science and Discovery, Isaac Asimov, HarperCollins Publishers, 1994.
	The Biographical Dictionary of Scientists, 2nd ed., Oxford University Press, 1994.
	Dictionary of Scientific Biography, Vols. 9, 10, 11, Charles C. Gillispile, Charles Scribner's Sons, 1973.
	Engineering in History, Richard S. Kirby and Sidney Withington, Arthur B. Darling, Frederick G. Kilgour, McGraw-Hill, 1956.
	The Invisible World of the Infrared, Jack R. White, Dodd, Mead & Company, 1984. The McGraw-Hill Encyclopedia of Science and Technology, 8th ed., Vol. 9, McGraw-Hill, 1997.
	Notable Twentieth-Century Scientists, Emily J. McMurray, Gale Research Inc., 1995.
	Pioneers of Modern Science, The World of Science, Bill MacKeith, Andromeda Oxford Limited, 1991.
	The Scientific 100. A Ranking of the Most Influential Scientists, Past and Present, John Simmons, Carol Publishing Group, 1996.
	Theory and Practice of Radiation Thermometry, David P. DeWitt., and Gene D. Nutter, John Wiley & Sons, 1988.