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碳卫星高光谱二氧化碳探测仪基于太阳夫琅禾费吸收线的在轨波长定标

TanSat ACGS On-orbit Wavelength Calibration Using the Solar Fraunhofer Lines

  • 摘要: 大气二氧化碳(CO2)探测仪(ACGS, Atmospheric Carbon dioxide Grating Spectrometer)搭载于中国全球二氧化碳观测科学试验卫星(TanSat),通过探测0.76 μm、1.61 μm、2.06 μm波段的反射太阳光谱,采用最优估计算法反演大气CO2浓度。满足高光谱分辨率和高精度CO2浓度反演需求,精确探测光谱波长的变化非常重要。本文以高分辨率太阳参考光谱的夫朗禾费吸收线作为参考基准,利用ACGS对太阳的观测光谱计算了ACGS三个谱段通道中心波长位置在一年内的变化情况。结果显示,三个谱段的波长变化在光谱分辨率10%以内,满足光谱定标精度需求。这种变化可能是由于仪器在轨状态变化引起,特别是在轨运行温度变化引起的。ACGS波长的微小变化需要在产品反演中进行修正。基于独立太阳夫琅禾费吸收线的在轨光谱定标方法不仅可以有效监测ACGS的光谱稳定性,还可以为L2产品的处理的提供参考信息。

     

    Abstract: Spectra measured using an atmospheric carbon dioxide grating spectrometer (ACGS) by the Chinese global carbon dioxide monitoring scientific experimental satellite (TanSat) in the bands of 0.76, 1.61, and 2.06 μm can be used for retrieving carbon dioxide (CO2) concentrations by fitting observations and simulations using an optimal estimation algorithm. Accurately detecting the change in the center wavelength is important because of its very high spectral resolution and accuracy requirement for product retrieval. Variations in the center wavelength for all the three bands of ACGS have been calculated at the locations of the Fraunhofer lines by comparing solar-viewing measurements and a high-resolution solar reference spectrum. Variations in magnitudes less than 10% of the spectral resolution for each band have been detected. Changes are probably caused by the vibration and instrument status difference between the ground and space, especially the temperature variation in the orbit. The scheme described herein can be used not only for monitoring spectral stability but also to gain spectral knowledge prior to the level-2 product processing. These minor temporal changes in the wavelength in the orbit should be corrected during the product retrieval.

     

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