Fast Spectral Calibration Method of Spectral Imager
WANG Jian-wei1, 2, LI Wei-yan1, SUN Jian-ying1, LI Bing1, CHEN Xin-wen1, TAN Zheng1, ZHAO Na1, LIU Yang-yang1, 3, LÜ Qun-bo1, 3*
1. The Key Laboratory of Computational Optic Imaging Technology, Academy of Opto-Electronics，Chinese Academy of Sciences, Beijing 100094，China
2. School of Instrumentation Science and Opto-electronics Engineering, Beihang University, Beijing 100191, China
3. School of Optoelectronics, University of Chinese Academy of Sciences, Beijing 100049, China
Abstract：Spectral calibration is determining the central wavelength of each channel of a spectrometer. To obtain the spectral radiance, it is usually necessary to calibrate the spectrometer and map the output value of the spectrometer to a physical quantity radiance. Different spectrometers, The spectral response is different, so it is necessary to determine the spectral response of each channel during the spectral calibration process. The spectral imager can be regarded as a composition of multiple spectrometers, and the center wavelength and spectral response of all points need to be calibrated. Since the birth of the first imaging spectrometer, its calibration method has been gradually fixed. A monochromator with the higher spectral resolution is required, and its spectral bandwidth is much smaller than the spectral response bandwidth of the spectral imager so that quasi-monochromatic light can be considered a pulse function. According to the characteristics of the pulse function, changing the wavelength of the quasi-monochromatic light and scanning the response wavelength range of the spectral imager is a process of sampling the spectral response function at intervals.. Therefore, the spectral imager’s central wavelength and spectral response function can be directly obtained from the spectral calibration data. With the development of technology, the sensitivity of the detector is getting higher and higher, and the resolution of the spectral imager is getting higher and higher. Higher requirements are put forward for the quasi-monochromatic light required for the spectrum calibration. However, the narrower the bandwidth of the quasi-monochromatic light, the lower its energy, and it takes longer to obtain data that meets the signal-to-noise ratio, which reduces the efficiency of calibration. In this paper, we combined the characteristics of quasi-monochromatic light’s spectral line type and spectral response function approximating to Gaussian function. Through theoretical analysis, a method of spectral calibration using wide-band quasi-monochromatic light is proposed, which can effectively reduce the calibration step of spectral calibration improves the efficiency of calibration and is suitable for the rapid calibration of spectral imagers. This method is used for the spectral calibration of a space-borne hyperspectral imager. The spectral imager uses a prism to split light and has the characteristics of non-linear dispersion. The spectral resolution varies from 2 to 18 nm, and there is a large curve of spectral lines. As a result, the center wavelength of each pixel is different, and spectral calibration is required for each pixel. To avoid the discontinuity of the central wavelength of the adjacent field of view caused by the calibration of the separate field of view, the quasi-monochromatic light spot emitted by the monochromator illuminates the entire slit, and a cylindrical lens and ground glass are placed between the slit and the monochromator. The cylindrical lens is used to converge the light perpendicular to the slit direction to improve the energy utilization; the ground glass is used to homogenize the light, and the presence of ground glass greatly reduces the energy entering the spectral imager. Combining the method proposed in this paper increases of the accuracy the bandwidth of monochromatic light, and the increase of energy have finally completed the rapid calibration of the spectral imager. The mercury lamp verifies that the spectral calibration accuracy is 0.23 nm.
Key words：Hyperspectral imaging; Spectral line bending; Spectral calibration
王建威，李伟艳，孙建颖，李 兵，陈鑫雯，谭 政，赵 娜，刘扬阳，吕群波. 光谱成像仪快速光谱定标方法研究[J]. 光谱学与光谱分析, 2022, 42(07): 2013-2017.
WANG Jian-wei, LI Wei-yan, SUN Jian-ying, LI Bing, CHEN Xin-wen, TAN Zheng, ZHAO Na, LIU Yang-yang, LÜ Qun-bo. Fast Spectral Calibration Method of Spectral Imager. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2022, 42(07): 2013-2017.
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