Snapshot hyperspectral imaging [1] is a method for capturing hyperspectral images during a single integration time of a detector array. No scanning is involved with this method, in contrast to push broom and whisk broom scanning techniques. The lack of moving parts means that [2] motion artifacts should be avoided. This instrument typically features detector arrays with a high number of pixels.
Although the first known reference to a snapshot hyperspectral imaging device—the Bowen "image slicer"—dates from 1938, [3] the concept was not successful until a larger amount of spatial resolution was available. With the arrival of large-format detector arrays in the late 1980s and early 1990s, a series of new snapshot hyperspectral imaging techniques were developed to take advantage of the new technology: a method which uses a fiber bundle at the image plane and reformatting the fibers in the opposite end of the bundle to a long line, [4] viewing a scene through a 2D grating and reconstructing the multiplexed data with computed tomography mathematics, [5] the (lenslet-based) integral field spectrograph, [6] a modernized version of Bowen's image slicer. [7] More recently, a number of research groups have attempted to advance the technology in order to create devices capable of commercial use. These newer devices include the HyperPixel Array imager a derivative of the integral field spectrograph, [8] a multiaperture spectral filter approach, [9] a compressive-sensing–based approach using a coded aperture, [10] a microfaceted-mirror-based approach, [11] a generalization of the Lyot filter, [12] and a generalization of the Bayer filter approach to multispectral filtering. [13] [14]
Slitless spectroscopy can be considered a basic snapshot hyperspectral imaging technique. Spaced point-like sources, such as a sparse field of stars, is a requirement to avoid spectrum overlap on the detector.
While snapshot instruments are featured prominently in the research literature, none of these instruments have seen wide adoption in commercial use (i.e. outside the professional astronomical community) due to manufacturing limitations. Thus, their primary venue continues to be astronomical telescopes. One of the main reasons for the popularity of snapshot devices in the astronomical community is that they offer large increases in the light collection capacity of a telescope when performing hyperspectral imaging. [15] [16] Recent applications have been in soil spectroscopy [17] and vegetation sciences. [18]
An optical spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the irradiance of the light but could also, for instance, be the polarization state. The independent variable is usually the wavelength of the light or a unit directly proportional to the photon energy, such as reciprocal centimeters or electron volts, which has a reciprocal relationship to wavelength.
The Very Large Telescope (VLT) is a facility operated by the European Southern Observatory, located on Cerro Paranal in the Atacama Desert of northern Chile. It consists of four individual telescopes, each equipped with a primary mirror that measures 8.2 meters in diameter. These optical telescopes, named Antu, Kueyen, Melipal, and Yepun, are generally used separately but can be combined to achieve a very high angular resolution. The VLT array is also complemented by four movable Auxiliary Telescopes (ATs) with 1.8-meter apertures.
The WIYN Observatory is owned and operated by the WIYN Consortium. Its 3.5-meter telescope is the second largest optical telescope at Kitt Peak National Observatory in Arizona. Most of the capital costs for the observatory were provided by the University of Wisconsin–Madison, Indiana University, and Yale University, while the National Optical Astronomy Observatory (NOAO) provides most of the operating services. The NOAO is an institution of the United States; it is the national optical observatory program and supports a collection of ground-based telescopes at Kitt Peak as well as other locations.
An optical filter is a device that selectively transmits light of different wavelengths, usually implemented as a glass plane or plastic device in the optical path, which are either dyed in the bulk or have interference coatings. The optical properties of filters are completely described by their frequency response, which specifies how the magnitude and phase of each frequency component of an incoming signal is modified by the filter.
Multispectral imaging captures image data within specific wavelength ranges across the electromagnetic spectrum. The wavelengths may be separated by filters or detected with the use of instruments that are sensitive to particular wavelengths, including light from frequencies beyond the visible light range, i.e. infrared and ultra-violet. It can allow extraction of additional information the human eye fails to capture with its visible receptors for red, green and blue. It was originally developed for military target identification and reconnaissance. Early space-based imaging platforms incorporated multispectral imaging technology to map details of the Earth related to coastal boundaries, vegetation, and landforms. Multispectral imaging has also found use in document and painting analysis.
Spectral imaging is imaging that uses multiple bands across the electromagnetic spectrum. While an ordinary camera captures light across three wavelength bands in the visible spectrum, red, green, and blue (RGB), spectral imaging encompasses a wide variety of techniques that go beyond RGB. Spectral imaging may use the infrared, the visible spectrum, the ultraviolet, x-rays, or some combination of the above. It may include the acquisition of image data in visible and non-visible bands simultaneously, illumination from outside the visible range, or the use of optical filters to capture a specific spectral range. It is also possible to capture hundreds of wavelength bands for each pixel in an image.
Hyperspectral imaging collects and processes information from across the electromagnetic spectrum. The goal of hyperspectral imaging is to obtain the spectrum for each pixel in the image of a scene, with the purpose of finding objects, identifying materials, or detecting processes. There are three general types of spectral imagers. There are push broom scanners and the related whisk broom scanners, which read images over time, band sequential scanners, which acquire images of an area at different wavelengths, and snapshot hyperspectral imagers, which uses a staring array to generate an image in an instant.
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 correspond 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.
Chemical imaging is the analytical capability to create a visual image of components distribution from simultaneous measurement of spectra and spatial, time information. Hyperspectral imaging measures contiguous spectral bands, as opposed to multispectral imaging which measures spaced spectral bands.
The Cosmic Origins Spectrograph (COS) is a science instrument that was installed on the Hubble Space Telescope during Servicing Mission 4 (STS-125) in May 2009. It is designed for ultraviolet (90–320 nm) spectroscopy of faint point sources with a resolving power of ≈1,550–24,000. Science goals include the study of the origins of large scale structure in the universe, the formation and evolution of galaxies, and the origin of stellar and planetary systems and the cold interstellar medium. COS was developed and built by the Center for Astrophysics and Space Astronomy (CASA-ARL) at the University of Colorado at Boulder and the Ball Aerospace and Technologies Corporation in Boulder, Colorado.
The Mount Abu InfraRed Observatory (MIRO) is located near the town Mount Abu in the state of Rajasthan, India. The observatory is at an altitude of 1680 metres and is adjacent to Guru Shikhar, highest peak of the Aravalli Range. The 1.2 m infrared telescope at It is the first major facility in India specifically designed for ground-based, infrared observations of celestial objects. Further the low amount of precipitable water vapour at Guru Shikhar makes it a good site for the infrared telescope observations. The site has been found to be good for astronomical observations.
Integral field spectrographs (IFS) combine spectrographic and imaging capabilities in the optical or infrared wavelength domains (0.32 μm – 24 μm) to get from a single exposure spatially resolved spectra in a bi-dimensional region. The name originates from the fact that the mesurements result from integrating the light on multiple sub-regions of the field. Developed at first for the study of astronomical objects, this technique is now also used in many other fields, such bio-medical science and Earth remote sensing. Integral field spectrography is part of the broader category of snapshot hyperspectral imaging techniques, itself a part of hyperspectral imaging.
A liquid crystal tunable filter (LCTF) is an optical filter that uses electronically controlled liquid crystal (LC) elements to transmit a selectable wavelength of light and exclude others. Often, the basic working principle is based on the Lyot filter but many other designs can be used. The main difference with the original Lyot filter is that the fixed wave plates are replaced by switchable liquid crystal wave plates.
This is a list of infrared topics.
The computed tomography imaging spectrometer (CTIS) is a snapshot imaging spectrometer which can produce in fine the three-dimensional hyperspectral datacube of a scene.
Photon etc. is a Canadian manufacturer of infrared cameras, widely tunable optical filters, hyperspectral imaging and spectroscopic scientific instruments for academic and industrial applications. Its main technology is based on volume Bragg gratings, which are used as filters either for swept lasers or for global imaging.
The NIRSpec is one of the four scientific instruments flown on the James Webb Space Telescope (JWST). The JWST is the follow-on mission to the Hubble Space Telescope (HST) and is developed to receive more information about the origins of the universe by observing infrared light from the first stars and galaxies. In comparison to HST, its instruments will allow looking further back in time and will study the so-called Dark Ages during which the universe was opaque, about 150 to 800 million years after the Big Bang.
Spatio-spectral scanning is one of four techniques for hyperspectral imaging, the other three being spatial scanning, spectral scanning and non-scanning, or snapshot hyperspectral imaging.
MIRI, or the Mid-Infrared Instrument, is an instrument on the James Webb Space Telescope. MIRI is a camera and a spectrograph that observes mid to long infrared radiation from 5 to 28 microns. It also has coronagraphs, especially for observing exoplanets. Whereas most of the other instruments on Webb can see from the start of near infrared, or even as short as orange visible light, MIRI can see longer wavelength light.
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