Spectral signature is the variation of reflectance or emittance of a material with respect to wavelengths. The spectral signature of stars indicates the composition of the stellar atmosphere. The spectral signature of an object is a function of the incidental EM wavelength and material interaction with that section of the electromagnetic spectrum.
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.
A staring array, also known as staring-plane array or focal-plane array (FPA), is an image sensor consisting of an array of light-sensing pixels at the focal plane of a lens. FPAs are used most commonly for imaging purposes, but can also be used for non-imaging purposes such as spectrometry, LIDAR, and wave-front sensing.
In imaging spectroscopy each pixel of an image acquires many bands of light intensity data from the spectrum, instead of just the three bands of the RGB color model. More precisely, it is the simultaneous acquisition of spatially coregistered images in many spectrally contiguous bands.
The normalized difference vegetation index (NDVI) is a widely-used metric for quantifying the health and density of vegetation using sensor data. It is calculated from spectrometric data at two specific bands: red and near-infrared. The spectrometric data is usually sourced from remote sensors, such as satellites.
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, usually to support analysis of the composition the object being imaged. The spectral data produced for a pixel is 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 image fusion process is defined as gathering all the important information from multiple images, and their inclusion into fewer images, usually a single one. This single image is more informative and accurate than any single source image, and it consists of all the necessary information. The purpose of image fusion is not only to reduce the amount of data but also to construct images that are more appropriate and understandable for the human and machine perception. In computer vision, multisensor image fusion is the process of combining relevant information from two or more images into a single image. The resulting image will be more informative than any of the input images.
Airborne Real-time Cueing Hyperspectral Enhanced Reconnaissance, also known by the acronym ARCHER, is an aerial imaging system that produces ground images far more detailed than plain sight or ordinary aerial photography can. It is the most sophisticated unclassified hyperspectral imaging system available, according to U.S. Government officials. ARCHER can automatically scan detailed imaging for a given signature of the object being sought, for abnormalities in the surrounding area, or for changes from previous recorded spectral signatures.
Electro-optical MASINT is a subdiscipline of Measurement and Signature Intelligence, (MASINT) and refers to intelligence gathering activities which bring together disparate elements that do not fit within the definitions of Signals Intelligence (SIGINT), Imagery Intelligence (IMINT), or Human Intelligence (HUMINT).
Full-spectrum photography is a subset of multispectral imaging, defined among photography enthusiasts as imaging with consumer cameras the full, broad spectrum of a film or camera sensor bandwidth. In practice, specialized broadband/full-spectrum film captures visible and near infrared light, commonly referred to as the "VNIR".
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 measurements 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.
Snapshot hyperspectral imaging 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 motion artifacts should be avoided. This instrument typically features detector arrays with a high number of pixels.
Video spectroscopy combines spectroscopic measurements with video technique. This technology has resulted from recent developments in hyperspectral imaging. A video capable imaging spectrometer can work like a camcorder and provide full frame spectral images in real-time that enables advanced mobility and hand-held imaging spectroscopy. Unlike hyperspectral line scanners, a video spectrometer can spectrally capture randomly and quickly moving objects and processes. The product of a conventional hyperspectral line scanner has typically been called a hyperspectral data cube. A video spectrometer produces a spectral image data series at much higher speeds (1 ms) and frequencies (25 Hz) that is called a hyperspectral video. This technology can initiate novel solutions and challenges in spectral tracking, field spectroscopy, spectral mobile mapping, real-time spectral monitoring and many other applications.
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.
Gaofen is a series of Chinese high-resolution Earth imaging satellites launched as part of the China High-resolution Earth Observation System (CHEOS) program. CHEOS is a state-sponsored, civilian Earth-observation program used for agricultural, disaster, resource, and environmental monitoring. Proposed in 2006 and approved in 2010, the CHEOS program consists of the Gaofen series of space-based satellites, near-space and airborne systems such as airships and UAVs, ground systems that conduct data receipt, processing, calibration, and taskings, and a system of applications that fuse observation data with other sources to produce usable information and knowledge.
