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摘要:
里奥滤光器广泛应用于太阳观测中进行光谱扫描成像，为保证其数据的有效性与准确性，必须定期对其进行在线标定。传统的在线标定方法要求环境光强具有较高稳定性，而本文提出了一种能够实时修正由环境扰动导致的太阳光强变化对标定过程影响的里奥滤光器在线标定方法。该方法通过单色光成像观测通道与里奥滤光器扫描成像观测通道联合观测的方式，以单色光成像通道的观测结果获得外界环境对太阳光强扰动的信息，在线校正滤光器的观测扫描数据，降低由环境扰动造成的太阳光强非稳定性带来的干扰。基于七波段太阳大气层析成像系统，对Hɑ(656.28 nm)扫描成像通道的里奥滤光器和TiO(705 nm)单色光成像通道进行了联合观测标定实验。实验结果表明，该方法有效消除了太阳光强非稳定性对滤光器实测光谱轮廓的影响，对中心波长位置定标精度优于0.005 nm，提升了里奥滤光器在线标定的准确性和对环境的适应性。
Abstract:Lyot filter is widely used in solar observation for spectra-scanning imaging. Calibration experiment at regular intervals is an important work to assure the accuracy and validity of Lyot filter. This paper comes up with a new method to conduct the Lyot filter calibration experiment on-line while traditional method requires perfect stability of environment. This method uses monochromatic imaging channel and Lyot filter scanning imaging channel simultaneously, and corrects the scanning data with monochromatic imaging data to correct the impact of environment. The instability of light source caused by disturbance of observation environment is reduced. We apply the calibration method in the high-resolution multi-wavelength solar imaging system to calibrate the Lyot filter in Hɑ (656.28) scanning imaging channel and correct the scanning data with TiO band (705 nm) observation data. The result shows that this method successfully eliminate the impact of the light instability on scanning curve of Lyot filter. The difference between the ideal center and the true center of the filter is more than 0.005 nm. The accuracy of the calibration experiment and the adaptability to environment are promoted.
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Overview: Lyot filter is widely used in solar observation for spectra-scanning imaging such as GST in America, SMART in Japan, ChroTel in Germany and NVST in China. As the instability caused by environment or mechanical error when the filter works, calibration experiment at regular intervals is an important work to assure the accuracy and validity of Lyot filter. Traditional method to calibrate the Lyot filter often requires the high quality of the observation weather, which makes the calibration experiment more difficult and wastes the valuable time of telescope observation time. To cover the shortage of traditional method, this paper comes up with a new method to conduct the Lyot filter calibration experiment on-line. This method uses monochromatic imaging channel and Lyot filter scanning imaging channel simultaneously. We assume that the vibration of the intensity of the monochromatic imaging is only caused by the disturbance of the observation environment. We can correct the spectra-scanning data with monochromatic imaging data to correct the impact of environment.
We apply the calibration method in the high-resolution multi-wavelength solar imaging system to calibrate the Lyot filter in Hɑ(656.28) scanning imaging channel and correct the scanning data with TiO band(705 nm) observation data. We calculate the correction coefficient with TiO band data, and use it to correct the spectra line pictured by Hɑ scanning imaging data. The result of line curve calibration experiment shows that this method successfully eliminate the impact of the light instability on scanning curve of Lyot filter, as the RMS of scanning curve and standard line is reduced from 482 to 456 and the shape of the scanning curve is closer to the standard line. Then we get a group of data to test the center wavelength of the spectra curve. As the result shows, the true center wavelength has a bias which is about 0.025 nm after the spectra scanning data is corrected by the TiO imaging data. According to the user guide, we change the work temperature of the filter. The center calibration experiment shows, after correcting the center wavelength by setting the work temperature of Lyot filter from 41.805 ℃ to 42.43 ℃, the difference between the idea center and the true center of the filter is reduced form about 0.025 nm to less than 0.005 nm. The center wavelength is well corrected after the calibration experiment.
As the result shows, the instability of light source caused by disturbance of observation environment is reduced and the efficiency of the calibration experiment is increased.
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图 2 可见光至近红外太阳大气不同高度活动区高分辨力多波段层析成像观测数据
Figure 2. Visible light to near-infrared image of different solar atmosphere layer observed by high-resolution multi-wavelength solar imaging system
图 5 (a) 光强修正前标定数据；(b)光强修正后标定数据
Figure 5. (a) Calibration data before correction; (b) Calibration data after correction
图 11 (a) 为光强修正前标定数据；(b)为光强修正后标定数据
Figure 11. (a) Calibration data before correction; (b) Calibration data after correction
表 1 七波段层析成像系统成像波段
Table 1. High-resolution multi-wavelength solar imaging system imaging channel
Wavelength/nm Spectra line Solar atmosphere layer Bandwidth/nm Resolution/(") Filter type 430.5 G band Photosphere 0.5 0.147 Interference 589.0 Na I line Chromospheres 0.003 0.034 Atomic 656.28 Hα line Chromospheres 0.025 0.135 Lyot 705.7 TiO band Photosphere 0.7 0.0345 Interference 854.2 Ca II IR line Chromospheres 0.02 0.203 Lyot 1083.0 He I line Chromospheres 0.05 0.246 Lyot 1565.3 Fe I line Photosphere 5 0.342 Interference 
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表 2 滤光器性能参数
Table 2. Performance of the Lyot filter
Attribute Value Center wavelength/nm 656.28 FWHM/nm ≤0.025 20% bandwidth ≤2.2倍FWHM 10% bandwidth ≤3倍FWHM Tunable range/nm ±0.5 Work temperature/℃ 42±1 Temperature stability/℃ ±0.02
下载: 导出CSV
表 3 三组标定实验均方根误差
Table 3. RMS of three calibration data groups
RMSE Group1 Group2 Group3 Before correction 468.3 599.5 367.6 After correction 442.6 529.5 359.7
下载: 导出CSV
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