Imaging spectroscopy

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Ash plumes on Kamchatka Peninsula, eastern Russia. A MODIS image.

Imaging spectroscopy is the simultaneous acquisition of spatially coregistered images in many spectrally contiguous bands. To be scientifically useful, such measurement should be done using an internationally recognized system of units. The image produced by imaging spectroscopy is similar to an image produced by a digital camera, except each pixel has many bands of light intensity data instead of just three bands: red, green and blue.

Imaging spectrometer data acquisition allows the quantitative and qualitative characterization of both, the surface and the atmosphere, using geometrically coherent spectrodirectional radiometric measurements. These measurements can then be used for the unambiguous direct and indirect identification of surface materials and atmospheric trace gases, the measurement of their relative concentrations, subsequently the assignment of the proportional contribution of mixed pixel signals (e.g., the spectral unmixing problem), the derivation of their spatial distribution (mapping problem), and finally their study over time (multi-temporal analysis).

1 Background
2 References
3 See also
4 External links

[edit] Background

About 300 years ago, in 1704, Sir Isaac Newton published in his ‘Treatise of Light’ (Newton, 1704) the concept of dispersion of light. He demonstrated that white light could be split up into component colours by means of a prism, and found that each pure colour is characterized by a specific refrangibility. The corpuscular theory by Newton was gradually succeeded over time by the wave theory. Consequently, the substantial summary of past experiences performed by Maxwell (1873), resulted in his equations of electromagnetic waves. But it was not before the 19th century, until the quantitative measurement of dispersed light was recognized and standardized.

A major contribution was Fraunhofer's discovery of the dark lines in the solar spectrum (Fraunhofer, 1817); and their interpretation as absorption lines on the basis of experiments by Bunsen and Kirchhoff (1863). The term spectroscopy was first used in the late 19th century and provides the empirical foundations for atomic and molecular physics (Born & Wolf, 1999). Significant achievements in imaging spectroscopy are attributed to airborne instruments, particularly arising in the early 1980s and 1990s (Goetz et al., 1985; Vane et al., 1984). However, it was not before 1999 until the first launch of an imaging spectrometer in space (for example the NASA Moderate-resolution Imaging Spectroradiometer).

Also scientific terminology and definitions evolve over time. Presently an imaging spectrometer is usually not any longer defined by a total minimum number of spectral bands (earlier, >10 spectral bands was a justification to use the term imaging spectrometer), rather than by a contiguous (or redundancy) statement of spectral bands.

The term hyperspectral imaging is sometimes used interchangeably with imaging spectroscopy. Due to its heavy use in military related applications, the civil world has established a slight preference for using the term imaging spectroscopy.

[edit] References

Born, M. & Wolf, E. (1999) Principles of Optics, 7 edn. Cambridge University Press, Cambridge.
Bunsen, R. & Kirchhoff, G. (1863) Untersuchungen über das Sonnenspektrum und die Spektren der Chemischen Elemente. Abh. kgl. Akad. Wiss., 1861.
Fraunhofer, J. (1817) Bestimmung des Brechungs- und Farbenzerstreuungs-Vermögens verschiedener Glasarten, in Bezug auf die Vervollkommnung achromatischer Fernrohre, Vol. 56, pp. 264-313. Gilberts Annalen der Physik.
Goetz, A.F.H., Vane, G., Solomon, J.E., & Rock, B.N. (1985) Imaging spectrometry for earth remote sensing. Science, 228, 1147.
Maxwell, J.C. (1873) A Treatise on Electricity and Magnetism Clarendon Press, Oxford.
Newton, I. (1704) Opticks: Or, a Treatise of the Reflexions, Refractions, Inflexions and Colours of Light Sam Smith and Benj. Walford, London.
Schaepman, M. (2005) Spectrodirectional Imaging: From Pixels to Processes. Inaugural address, Wageningen University, Wageningen (NL).
Vane, G., Chrisp, M., Enmark, H., Macenka, S., & Solomon, J. (1984) Airborne Visible Infrared Imaging Spec-trometer (AVIRIS): An Advanced Tool for Earth Remote Sensing. European Space Agency, (Special Publication) ESA SP, 2, 751.