Changchun Institute Of Optics Analyzes The Development Status And Trends Of Filter Spectroscopy-type Hyperspectral Cameras

Hyperspectral cameras can combine imaging technology with spectral detection technology, and while imaging the spatial features of a target, they can form multiple narrow bands for each spatial image element to achieve continuous spectral coverage, and the different spectral information can fully reflect the differences in physical structure and chemical composition within a feature. Compared with traditional two-dimensional spatial imaging, hyperspectral cameras can acquire spatial and spectral information about the target. At a specific spatial resolution, they can achieve the unique continuous spectral features of the ground features in a wide range of spectral bands, which has significant advantages for accurately identifying and detecting the ground features. It has considerable application value in agriculture, forestry, water, soil, mining, and other resource surveys and environmental monitoring.

With the rapid development of filter coating technology, the development of filter spectroscopic hyperspectral cameras has been extensively promoted. Hyperspectral cameras based on the filter spectroscopic principle have become an essential part of hyperspectral remote sensing loads with the advantages of large bandwidth, high spatial resolution, high spectral resolution, and light and small size. They are widely used in the network of micro-nano-satellite hyperspectral constellations.

According to McMasters Consulting, Liu Chunyu's research group at the Changchun Institute of Optics and Precision Mechanics and Physics, Chinese Academy of Sciences, recently published an article in the journal Infrared and Laser Engineering on the topic of "Status and trends of filter spectroscopic hyperspectral camera development." Liu Chunyu is mainly engaged in the research of optical system design and the overall design of optoelectronic systems.

Schematic diagram of hyperspectral imaging principle

This research mainly reviews the filter spectroscopic hyperspectral cameras, introduces the typical filter spectroscopic on-board hyperspectral imaging payloads at home and abroad, and the filter spectroscopic hyperspectral imaging systems under development on the ground, and analyses the technical solutions, performance indexes, and application prospects of these systems, and explains the technical characteristics, advantages, and disadvantages of the filter spectroscopic principle-based hyperspectral cameras. The technical aspects, benefits, and drawbacks of hyperspectral cameras based on the filter spectroscopy principle are explained, and finally, the development trend of filter spectroscopic cameras is foreseen.

The filter wheel hyperspectral camera uses the filter wheel as the spectral element to obtain spectral images of different wavelength bands by rotating the filter wheel, thus completing the spectral separation of complex to monochromatic light. The critical component of a filter wheel hyperspectral camera is the filter wheel, which a filter wheel can replace the corresponding spectral range according to the different observation bands. With the development of spectral imaging technology, the number of detection bands is increasing, and the filter wheel can no longer meet the wide range of high-resolution observation, so it is increasingly used in multispectral detection.

Tunable filter hyperspectral cameras use tunable filters as spectral components and are mainly divided into Liquid Crystal Tunable Filter (LCTF) hyperspectral cameras, Acousto-Optic Tunable Filter (AOTF) hyperspectral cameras, and MEMS tunable FP cavity cameras. MEMS Tunable Fabry-Perot Cavity Filters (AOTF) hyperspectral cameras.

The wedge-shaped filter hyperspectral camera, also known as a tunable filter hyperspectral camera, enables continuous sampling in spectral and spatial regions. The concept is to use a wedge-shaped multilayer thin-film medium as a filter and to mount it near a two-dimensional array detector so that several image elements of the sensor correspond to a particular spectral band of the tunable filter. Depending on the correspondence between the bars of the gradient filter and the image elements of the detector, gradient filter hyperspectral cameras can be divided into linear gradient and filter array types.

Structure and spectroscopy of a progressive linear filter

Quantum dots, also known as "nanocrystals," are inorganic materials that are highly stable and have a radius smaller than the radius of a large exciton wave. Integrating different types of quantum dots allows simultaneous detection of different wavelengths, which is the principle behind the development of the quantum dot spectrometer (CQD). The traditional concept of spectrometers with high-precision optical and mechanical components is bulky, expensive, complex, and severely limited in application.

Principle diagram of NIR quantum dot spectrometer

In general, the filter spectroscopy-type hyperspectral camera is in its initial stage, and its spectral resolution still needs to be comparable to the high-precision grating dispersion spectroscopy method. In addition, the combination of filter and detector will further improve the spectral resolution of the system, which can even be comparable to high-precision grating dispersive spectroscopy. Therefore, combining filter and detector wafers is also a significant development trend of coated hyperspectral cameras. It is easy to see that the development of filter-based hyperspectral cameras will drive a disruptive growth in the field of hyperspectral imaging, which will, in turn, cause the development of hyperspectral remote sensing technology for micro-nano-satellites and lay the technical foundation for the future operational operation of micro-nano-hyperspectral satellite constellations in orbit to serve the national economy better.

This project was supported by the National Natural Science Foundation of China (41504143), the Research Equipment Development Project of the Chinese Academy of Sciences (YJKYYQ20190044), the Natural Science Foundation of Anhui Province (1908085 ME135), and the Youth Innovation Promotion Council of the Chinese Academy of Sciences (2016203).