Imaging spectrometer

An imaging spectrometer is an instrument used in hyperspectral imaging and imaging spectroscopy to acquire a spectrally-resolved image of an object or scene, often referred to as a datacube due to the three-dimensional representation of the data. Two axes of the image corresponds to vertical and horizontal distance and the third to wavelength. The principle of operation is the same as that of the simple spectrometer, but special care is taken to avoid optical aberrations for better image quality.

Example imaging spectrometer types include: filtered camera, whiskbroom scanner, pushbroom scanner, integral field spectrograph (or related dimensional reformatting techniques), wedge imaging spectrometer, Fourier transform imaging spectrometer, computed tomography imaging spectrometer (CTIS), image replicating imaging spectrometer (IRIS), coded aperture snapshot spectral imager (CASSI), and image mapping spectrometer (IMS).

Imaging spectrometers are used specifically for the purpose of measuring the spectral content of light and electromagnetic light. The spectral data gathered is used to give the operator insight into the sources of radiation. Prism spectrometers use a classical method of dispersing radiation by means of a prism as a refracting element.

The imaging spectrometer works by imaging a radiation source onto what is called a “slit” by means of a source imager. A collimator collimates the beam that is dispersed by a refracting prism and re-imaged onto a detection system by a re-imager. Special care is taken to produce the best possible image of the source onto the slit. The purpose of the collimator and re-imaging optics are to take the best possible image of the slit. An area-array of elements fills the detection system at this stage. The source image is reimaged, every point, as a line spectrum on what is called a detector-array column. The detector array signals supply data pertaining to spectral content, in particular, spatially resolved source points inside source area. These source points are imaged onto the slit and then re-imaged onto the detector array. Simultaneously, the system provides spectral information about the source area and its line of spatially resolved points. The line is then scanned in order to build a database of information about the spectral content.

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