The infrared part of the spectrum has been used for many different scientific, military, medical, forensic, civilian, industrial, practical, astronomical, and microscopic applications. One good place to read more about all this is Hudson. Another is the September 1959 issue of the Proceedings of the Institute of Radio Engineers (Proc. IRE), now Proceedings of the IEEE. We will discuss just enough of these to give the flavor of the diversity. Astronomical applications have been in the news in large measure because of the Infrared Astronomical Satellite (IRAS) and Shuttle Infrared Telescope Facility (SIRTF). Because the infrared part of the spectrum gives much thermal information and other clues that the visible does not, it is an important part of the astronomical observational arsenal. Long wavelengths are important, as is rising above the absorptions of the atmosphere. Our weather system is gradually being understood better as a result of many infrared measurements of temperature profiles and cloud distributions. The railroads have benefited from hot-box detectors. These devices, as simple as they were, can be placed by the side of the tracks to look for hot spots that are indicative of journal boxes that have lost their lubricants. Houses can now have infrared warning and intrusion detectors. They can also be analyzed for the efficacy of their insulation. Although they have been investigated, aircraft collision warning systems using infrared have not been introduced.
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