Analysis and Correction of On-Orbit Spectral Drift of FY-3E Solar
Spectral Irradiance Monitor Visible Band
TAN Xiao-feng1, 2, QI Jin2, 3, 4*, LI Zhan-feng5, ZHANG Peng6, 7*
1. Chinese Academy of Meteorological Sciences, Beijing 100081, China
2. National Satellite Meteorological Center (National Center for Space Weather), Beijing 100081, China
3. Innovation Center for FengYun Meteorological Satellite (FYSIC), Beijing 100081, China
4. Key Laboratory of Radiometric Calibration and Validation for Environmental Satellites, China Meteorological Administration, Beijing 100081, China
5. Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China
6. Meteorological Observation Center, China Meteorological Administration, Beijing 100081, China
7. State Key Laboratory of Environment Characteristics and Effects for Near-Space, Beijing 100081, China
摘要： 太阳辐照度光谱仪（SSIM）是我国首台自主研制的在大气层顶开展太阳连续光谱监测的跟踪式辐照度光谱仪，它搭载于第二代极轨气象卫星风云三号黎明星（FY-3E）。SSIM的光谱范围为165~2 400 nm，在紫外和可见光波段具有1 nm的光谱分辨率，以及0.1和0.25 nm间隔的采样率，能够捕捉太阳精细光谱特征。针对SSIM可见光波段获取的太阳光谱结构，利用国际上最新发布的高分辨率太阳参考光谱TSIS-1 HSRS(Total and Spectral Solar Irradiance Sensor-1 Hybrid Solar Reference Spectrum, TSIS-1 HSRS)为定标基准，分析2021年9月至2023年11月期间光谱的在轨变化特征，评估在轨光谱定标精度。基于太阳参考光谱的夫琅禾费吸收线特征，利用仪器发射前测定的光谱狭缝函数卷积后得到与仪器特征相匹配的参考光谱，筛选出9个夫琅禾费特征波长，基于光谱匹配方法计算波长偏移，分析在轨波长偏移随时间的变化特征，并建立精细化订正方法提升仪器在轨光谱定标精度。针对晨昏轨道对日观测的轨道运动特征，首先分析了多普勒频移的年变化特征，评估其在可见光波段可引起的波长最大偏移区间为-0.005~0.001 nm(700 nm 处)。基于太阳夫琅禾费吸收线方法发现可见光波段光谱漂移的长期变化呈现周期性波动，与在轨初期相比，410 nm吸收线波长偏移的波动范围大致为-0.032~0.025 nm，分析认为波长偏移与仪器温度的周期性波动有关，各特征波长偏移与SSIM光栅温度的相关系数在-0.766~-0.964之间，存在强的负相关。针对波段内不同光谱位置的漂移特征，利用光谱匹配方法分段滑动计算波长偏移，再对其进行拟合修正，修正结果显示光谱定标精度优于0.028 nm，消除了卫星发射过程和在轨工作环境变化对光谱精度的影响，以及仪器温度周期性波动导致的波长偏移，长期稳定性较好，有效提升了SSIM在轨光谱定标精度。本文可为宽波段太阳光谱仪的在轨光谱定标研究提供参考。
关键词：太阳光谱辐照度；光谱定标；太阳参考光谱；可见光波段
Abstract：The Solar spectral irradiance monitor (SSIM) is China's first spaceborne solar irradiance spectrometer designed to measure solar continuum spectrumat the top of the atmosphere. It is mounted on the Fengyun-3E (FY-3E) satellite, the fifth satellite in the second generation of Chinese polar-orbit meteorological satellites. SSIM covers a spectral range from 165 to 2 400 nm, with a spectral resolution of 1 nm and sampling intervals of 0.1 and 0.25 nm in the ultraviolet and visible bands, which can capture fine solar spectrum characteristics of the sun. This study evaluated the spectral calibration accuracy of the SSIM visible band using the latest Total and Spectral Solar Irradiance Sensor-1 Hybrid Solar Reference Spectrum (TSIS-1 HSRS) as reference, with measurements from September 2021 to November 2023. By convoluting the pre-launch spectral slit function with TSIS-1 HSRS, a reference spectrum was generated to match the SSIM's characteristics. Using the spectrum matching method, nine solar Fraunhofer lines were selected to characterize wavelength shifts. The temporalvariationof spectral drift was analyzed, and a refined correction method was developed to improvethe spectral calibration accuracy of SSIM. Considering the characteristics of the early morning orbit, the annual variation of the Doppler shift was first analyzed, revealing the maximum wavelength shift of -0.005 to 0.001nm at 700 nm. Based on the assessment results of the Fraunhofer lines, the long-term variation of wavelength shifts in the visible band exhibited periodic fluctuations, with the shift of 410 nm varying from -0.032 to 0.025 nm compared to the initial on-orbit state. Further analysis indicates that the spectral driftis strongly correlated with the periodic fluctuations in the grating temperature of SSIM, with correlation coefficients between the wavelength shifts of the Fraunhofer lines and the grating temperature ranging from -0.766 to -0.964. Considering the drift characteristics on different spectral regions, the method of segmenting and sliding to calculate wavelength shifts and then fitting them for correction has been applied to the SSIM visible band, which shows that the results of spectral calibration accuracy are better than 0.028 nm. This method eliminates the impact of satellite launch, environmental changes on spectral accuracy, and also temperature fluctuations induced spectral drift. It has good long-term stability and effectively improves the on-orbit spectral calibration accuracy of SSIM. This paper provides a reference for the research on the on-orbit spectral calibration of wide-band solar spectrometers.
Key words：Solar spectral irradiance; Spectral calibration; Solar reference spectrum; Visible band
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