Why Spectral Imaging?
Why Spectral Imaging?
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Spectral Imaging combines the strength of conventional imaging with that of spectroscopy to accomplish tasks that separately each can not perform. It allows performing spectroscopy from a-far using remote sensing techniques. The product of a spectral imaging system is a "stack" of images of the same object or scene, each at a different spectral narrow band (or "color"). For a tutorial covering the basics please browse the Hyperspectral Newsletter and view a list of related resources including links to most of the major organizations dealing with the technology. The field is divided into techniques called multispectral, hyperspectral and ultraspectral. While no formal definition exists, the difference (counter to various popular notions) is not based on the number of bands. Multispectral deals with several image at discrete and somewhat narrow bands. The "discrete and somewhat narrow" is what distinguishes multispectral in the visible from color photography. Multispectral sensor may have many bands covering the spectrum from the visible to the longwave infrared. Multispectral images do not produce the "spectrum" of an object. Hyperspectral deals with imaging narrow spectral bands over a contiguous spectral range, and produce the spectra of all pixels in the scene. So a sensor with only 20 bands can also be hyperspectral when it covers the range from 500 to 700 nm with 20 10-nm wide bands. (While a sensor with 20 discrete bands covering the VIS, NIR, SWIR, MWIR, and LWIR would be considered multispectral.) Ultraspectral is typically reserved for interferometer type imaging sensors with a very fine spectral resolution. These sensor often have a low spatial resolution of several pixels only, a restriction imposed by the high data rate.
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