Imaging spectrometer is a new generation of sensor.It was officially developed in the early 1980s.The main purpose of developing this kind of instrument is to obtain a large number of narrow band continuous spectral images of ground objects, and at the same time obtain almost continuous spectral data of each pixel, so it is called imaging spectrometer.Imaging spectrometer is mainly used for hyperspectral aerial remote sensing.Hyperspectral has also begun to be used in the field of aerospace remote sensing.[1]
A new type of sensor that is developing rapidly in the world is called imaging spectrometer. It is an instrument that acquires image information in a multi-channel, continuous and high spectral resolution way.By organically combining the traditional space imaging technology with the ground object spectrum technology, it can achieve the simultaneous acquisition of dozens to hundreds of wavebands in the same areaSurface reflection spectrumImage.
Imaging spectrometer basically belongs toMultispectral scannerIts structure is the same as that of CCD linear array push broom scanner and multispectral scanner, except that there are many channels and the band width of each channel is very narrow.[2]
Development background
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At the end of 1970s and the beginning of 1980sSpectral characteristics of ground objectsOn the basis of, a concept has been formed: if continuous narrow band imaging can be achieved, then it is possible to realize direct recognition of ground minerals, resulting in an imaging spectrum technology that combines spectrum and image.1983 USAJet Propulsion LaboratoryThe first airborne imaging spectrometer (AIS-1) was developed, and then many countries, including China, have successfully developed a series of imaging spectrometers, including the optical mechanical scanning type based on the linear array detector, the solid-state push scanning type based on the area array detector, and the parallel scanning type based on the area array detector and the light machine.
classification
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Imaging spectrometers can be divided into two types according to their different structures.One is an imaging spectrometer with an array detector and a pushbroom scanner, which uses a linear array detector to scan, and uses dispersion elements and an array detector to complete spectral scanning.The line array detector and its movement along the orbit direction are used to complete space scanning.
Imaging spectrometer with array
The other is to use line array detector to addOptical mechanical scannerThe imaging spectrometer uses a point detector to collect spectral information, which is divided into different wavebands after passing through the dispersion element. On different elements of the online array detector, the spatial scanning is completed by the point scanning mirror swinging in the plane perpendicular to the orbital direction and moving along the orbital direction, while the spectral scanning is completed by the line detector.[1]
Imaging spectrometer with needle
merits and demerits
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Imaging spectrometer data has the advantage of extremely high spectral resolution. At the same time, due to the huge amount of data, it is difficult to store, retrieve and analyze.In order to solve this problem, the data must be compressed, and the two-dimensional structure expression method of conventional remote sensing images with a small number of bands cannot be used.Image cube is a new data format developed to adapt to the expression of imaging spectral data.The image on the front side of the cube is a combination of three bands of images selected by ourselves. It is a two-dimensional image representing spatial information, and below it is a superposition of single band images;The information located at the edge of the cube represents the encoded value or reflectivity of the surface radiance of each pixel at the edge of each single band image. This image representation is also called image cube.
From a geometric point of view, the imaging mode of the imaging spectrometer isMultispectral scannerSame, or similar to the CCD line array sensor. Therefore, the method similar to the multispectral scanner and CCD line array sensor data can be used in geometric processing.,Imaging spectrometer only focuses on improving spectral resolution, but its spatial resolution is low (tens or even hundreds of meters).It is precisely because imaging spectrometer can obtain narrow band widthMultiband imageData, so it is mostly used for spectral analysis and recognition of ground objects.In particular, since the imaging spectrometer works in visible light, near infrared and short wave infrared bands, it is very effective for special mineral exploration and sea color survey, especially for mineralized altered rocks with diagnostic spectral characteristics in short wave bands.[1]
The analysis and processing of hyperspectral remote sensing information focuses on the expansion and quantitative analysis of image information in the spectral dimension. The key technologies of its image processing mode include: ⑴ the display of hyperspectral image information, such as the generation of image cubes; ⑵Spectral reconstruction, that is, calibration, quantification and atmospheric correction models and algorithms of imaging spectral data, based on which image spectral conversion of imaging spectral information is realized; ⑶Spectral coding, especially the spectral absorption position, depth, symmetry and other spectracharacteristic parameter Algorithm of; ⑷Features based on spectral databaseSpectral matchingIdentification algorithm; ⑸Mixed spectral decomposition model; (6)Surface based on spectral modelBiophysical chemistryProcess and parameter identification andinversionAlgorithm.
High end imaging spectrometer adopts transmissive phaseholographicdiffraction grating , which is in thevisible lightreachNear infraredBand has lowStray light, Lowabsorptivitycharacteristic;Because the core part is sealed in glass or other transparent materials, it has a long life, is easy to clean, and is scratch resistant. It is very suitable for various harsh outdoor applications.
The imaging spectrometer mainly works in push broom mode. In order to realize the scanning process, it is usually driven by an external scanning platforma spectrometerfunction;Because the scanning platform is relatively bulky and increases power consumption, which brings a lot of inconvenience to field work, the latest imaging spectrometer cancels the scanning platform and changes to a built-in scanning design, which reduces the weight and energy consumption of the whole machine, and can directly conduct vertical downward measurement, which is more conducive to field use.
application
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highspectral resolution Imaging spectral remote sensing originated from the research of geological mineral recognition mapping, and gradually expanded to the research of vegetation ecology, marine coastal water color, ice and snow, soil and atmosphere.
On the basis of hyperspectral measurement, the imaging spectrometer has the advantage of spectrum integration, which can accurately detect the characteristics of different stress symptoms of crops at one point of the leaves, and can also obtain the spectral information of stressed crops, which can comprehensively reflect the degree of stress on crops by combining points and planes.Therefore, imaging hyperspectral has become a research hotspot at home and abroadHyperspectral imaging technologyQuantitative extraction of various stress characteristics suffered by crops, analysis of leaves and local areas of leaves based on high-resolution images, so as to carry out mechanism detection research on a more microscopic scale.
It is precisely because imaging spectrometer can obtain narrow band widthMultiband imageData, so it is mostly used forspectral analysisAnd identification.In particular, since the working wave band of the imaging spectrometer isvisible light、Near infrared, shortwave infrared, so it is very effective for special mineral exploration and sea color survey, especially for mineralizationAltered rockIt has diagnostic and spectral characteristics in short wave band.[3]
