What is the principle of imaging spectrometer? What are the applications? -Laisen Optics

Imaging spectrometer was developed on the basis of multispectral remote sensing imaging technology in 1980s. It obtains hyperspectral images of scenes or targets with hyperspectral resolution, and is widely used in aviation, spacecraft, land, atmosphere, ocean and other observations. Hyperspectral imager can be applied to the accurate classification, recognition and feature information extraction of ground objects. After establishing the model of hyperspectral remote sensing information processing and quantitative analysis, the automation and intelligence level of hyperspectral data processing can be improved. Because of the great advantage of high spectral resolution of imaging spectrometer, it is becoming a hot spot in the field of remote sensing and the main technical means of contemporary space observation to obtain multiple continuous-band spectral images of ground objects while observing the earth from space, so as to directly identify the surface substances of the earth from space. Using spectral imager on the ground has also made great achievements, such as scientific research, environmental protection of industry, agriculture and forestry.

This paper mainly introduces the basic principle of hyperspectral imager and its application in agriculture, forestry and environmental protection.

Working principle and structure of 1 system

Hyperspectral imager combines imaging technology with spectral technology, which can detect the spatial characteristics of objects, and discretize each spatial pixel to form dozens to hundreds of continuous spectral coverage with a bandwidth of about 10nm.

1. 1 working principle of the system

The reflected light of the ground object is imaged on the plane of the slit through the objective lens, and the slit acts as a diaphragm, so that the image of the ground object strip in the track crossing direction passes through, while blocking other light. The radiation energy of the ground target passes through the pointing mirror, is collected by the objective lens, is irradiated on the dispersive element through the enhanced collimation of the slit, is spectrally dispersed by the dispersive element in the vertical stripe direction, and is converged and imaged on the sensor by the converging mirror. The two-dimensional CCD area array detection elements used by the sensor are distributed on the focal plane of the spectrometer. The horizontal direction of the focal plane is parallel to the slit, which is called the spatial dimension. On each row of horizontal photosensitive elements, there is a ground object image with a spectral band. The vertical direction of the focal plane is the dispersion direction, which is called spectral dimension. On each column of photosensitive elements, there is a spectral dispersion image of a spatially sampled field of view (pixel). In this way, each frame of image data of the area array detector is the spectral data of the ground target strip in the cross-track direction, and the spectral images are continuously recorded at a certain rate with the motion of the spacecraft, so that the spectral data of each pixel in the ground two-dimensional images and graphics can be obtained, that is, the image cube.

Composition of data acquisition system of 1.2 spectral imager

Spectral imager consists of optical system, signal front-end processing box and data acquisition and recording system.

Data playback and preprocessing are completed by special software on a high-performance microcomputer. The software has the following functions: data backup; Fast playback; Data standardization and format conversion; Image segmentation and interception; Standard format image data generation, etc.

Application of 2 imaging spectrometer

The application scope of imaging spectrometer covers many fields such as chemistry, physics, biology and medicine. It has important application value for chemical analysis and molecular structure determination from pure qualitative to highly quantitative. For example, in biochemical research, Raman spectra can be used to identify the types of some substances, and intermolecular forces and internal forces can be quantitatively understood by measuring the vibration and rotation frequencies of molecules, and the symmetry, geometry and arrangement of atoms in molecules can be inferred, thermodynamic functions can be calculated, vibration-rotation Raman spectra and rotation Raman spectra can be studied, and data about molecular constants can be obtained. For nonpolar molecules, because they do not absorb or emit rotation and vibration spectra, many information such as vibration rotation energy and symmetry are reflected in the scattering spectrum. For polar molecules, although a lot of knowledge of molecular parameters can be obtained through infrared spectrum, in order to obtain more complete data, infrared spectrum and Raman spectrum are often observed at the same time. They have different selection rules and can provide complementary data. Now the combination of these two spectra has become a powerful research tool.

Spectral imager also has a wide and far-reaching application prospect in land use, crop growth, classification, pest detection, marine water color measurement, urban planning, oil exploration, core landforms and military target identification. The most widely used fields of hyperspectral imager in visible near infrared spectrum are vegetation and ocean; The reflectance spectral characteristics of vegetation mainly depend on the content and composition of chlorophyll in leaves, and normal growing plants have typical spectral shapes; Factors such as poor growth, diseases and insect pests, and diseases induced by underground metal minerals will cause the change of reflection intensity ratio and the slight deviation of absorption spectrum characteristics (0.68μm). The observation of this shift requires that the spectral resolution of hyperspectral imager is better than 5 nm and the signal-to-noise ratio is higher than 65,438+000. Only visible light can be observed in the light wave range, and the wavelength range with the best penetrating power is 0.45 0.60μ m (blue light to yellow light), also known as "window of the ocean". Visible hyperspectral imager can observe the distribution of suspended solids, plankton and chlorophyll in the ocean, but it needs not only high spectral resolution, but also high radiation sensitivity (signal-to-noise ratio above 500) to obtain the quality and quantity information of suspended solids in the ocean surface.

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