|Hyperspectral imaging (HSI) technology takes advantage of the wavelength composition of electromagnetic radiation (EMR). Almost all electromagnetic radiation, including visible light, is comprised of a mixture of many, many different wavelengths of EMR. Typically, the wavelengths of interest for HSI range from the low end of the visible spectrum (violet) through the high end of the visible spectrum (red), through near-infrared (NIR), short-wave infrared (SWIR) and mid-wave infrared (MWIR) to long-wave infrared (LWIR). Long-wave infrared is also often called thermal infrared. Most HSI systems utilize only part of this range of interest.
In a hyperspectral sensor, EMR is captured and focused onto a diffraction grating. The diffraction grating spreads the incident electromagnetic radiation into its constituent wavelengths. The effect is very similar to that achieved when visible light passes through a glass prism--the light is spread into its constituent colors. With a diffraction grating, however, the wavelength spread is predictable and very accurate.
The EMR that reflects from the diffraction grating is directed to a set of collectors that convert the incident light of various wavelengths into electrical signals. Typically, the collectors are contained on an electronic chip that is very much like the electronic chips that are found in digital cameras, except the chips in an HSI sensor are usually sensitive to much wider ranges of EMR (a digital camera is sensitive only to visible light). The electrical signals from the chip are passed to a computer that processes the data and presents the user with information that can be used to reach conclusions about the source of the captured EMR.
For a more thorough explanation of HSI technology, please read "An Introduction to Hyperspectral Imaging Technology" (5.4 MB).
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