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Spectroscopy is a venerable science and technology. Fraunhofer used it to investigate the composition of the sun. It has been used to investigate atomic structure, utilizing the spectral lines in emission and absorption exhibited by various elements. Our understanding of the nucleus and electronic orbits, as well as spin states, has been greatly enhanced by the information generated by high-resolution spectroscopy, for the most part in the visible portion of the spectrum. Chemical analysis of myriad compounds and solutions has been accomplished with the aid of infrared spectroscopy, since the characteristic absorptions of molecules occur in the near-infrared portion of the spectrum. In a somewhat different context, the use of colorimetry in the medical laboratory for the investigation of cholesterol, blood sugar, and other vital âchemistriesâ is a form of crude spectroscopy. It has also been used for checking automobile emissions, determining blood alcohol level, monitoring smokestack pollution, and ensuring the viability of crops. It is venerableâand very modern.
Perhaps the first images were those said to be obtained by Narcissus. Technological imaging may not be that old, but it dates back, at least, to the days of the camera obscura. Pinhole cameras, simple camera lenses, silver halide emulsions, modern CCD silicon-detector camcorders, television, and many of the technologies we now take for granted are part of the science and technology of imaging.
These two technologies combine to form the relatively new discipline of imaging spectrometry or spectrometric imaging.
In one sense of the word, every image is a spectral image: it is formed by the radiation in a limited part of the entire electromagnetic spectrum. But most of us would not consider a television image to be a spectral image, nor would a television set be an imaging spectrometer. In its most limited sense, an imaging spectrometer is a device that provides an image in at least two different spectral bands. In this sense, some infrared imagers that operate in both the 3â5 μm and 8â12 μm bands are spectral imagers, and they can make use of the relative signals in the two bands to make crude inferences of temperature and emissivity. But we would not consider these to be imaging spectrometers either.
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