大气CO2卫星遥感中植物叶绿素荧光影响的校正

大气CO₂卫星遥感监测的关键在于高精度，而植物叶绿素荧光存在与大气散射相似的光谱特征，干扰大气散射相关参数的反演结果，从而影响CO₂的反演精度。因植物叶绿素荧光强度微弱且影响特征与大气散射高度相关而难以准确校正。鉴于现有大气CO₂卫星遥感精度不足，以及植物叶绿素荧光对大气CO₂反演存在不可忽视的影响程度和复杂性，设计了O₂-A、1.6和2.06 μm CO₂三个光谱带协同的参数化校正方法。首先通过对大气散射采取基于光子路径长度概率密度函数（PPDF）的参数化建模，降低叶绿素荧光与大气散射参数的光谱相关性；其次，针对叶绿素荧光强度弱，难以准确反演的问题，基于轨道碳观测器（OCO-2）的叶绿素荧光产品构建了5km分辨率的全球叶绿素荧光先验信息库，增强CO₂与叶绿素荧光同步反演中对叶绿素荧光的先验约束，提高叶绿素荧光的反演精度。通过O₂-A、1.6和2.06 μm CO₂三个光谱带的协同同时反演大气散射、叶绿素荧光和大气CO₂，并结合叶绿素荧光丰富的先验信息，能够较准确剥离大气散射和叶绿素荧光而提高大气CO₂的反演精度。选择叶绿素荧光强度明显较高的柱总碳观测网络（TCCON）中的Park Falls（45.945°N，90.273°W）站点开展验证，对该站点近4年每年8月份的温室气体观测卫星（GOSAT）数据进行反演，发现植被叶绿素荧光导致GOSAT XCO₂反演结果系统偏低2×10-6(ppm)左右，通过本文的方法进行校正，反演结果的低估程度有明显改善，最大低估由2.58 ppm降低到1.49 ppm，且离散程度也有一定程度的改善，明显控制了CO₂反演中叶绿素荧光的影响，对于实现1%（~4 ppm）的CO₂反演精度来说，提供了有力支撑。

Correction the Effect of Plant Chlorophyll Fluorescence on Atmospheric Carbon Dioxide Satellite Monitoring

For atmospheric Carbon dioxide(CO2)satellite monitoring,high precision is the most important.However,because of the high similarity of spectra between plant chlorophyll fluorescence and atmospheric scattering effects,the atmospheric scattering effects were always misinterpreted and CO2 retrieval errors were caused.The minor radiance and high spectral similarity of the plant chlorophyll fluorescence made it hard to retrieve and correct.Considering the non-negligible effects of plant chlorophyll fluorescence on CO2 retrieval,we designed a correction method based on atmospheric scattering effects parameterization using three spectral bands of O2-Aband,1.6 and 2.06μm CO2 band to retrieve chlorophyll fluorescence,photonpath-length probability density function(PPDF)parameters and CO2 simultaneously.Firstly,atmospheric scattering effects were parameterized using the PPDF model to reduce its spectral similarity with the plant chlorophyll fluorescence.Secondly,the prior information database with 5 km resolution of plant chlorophyll fluorescence was built using plant chlorophyll fluorescence products from the Orbiting Carbon Observatory(OCO-2),which can strength the prior constraints on chlorophyll fluorescence retrievals and improves its retrieval precision.Through disentangling and quantifying the atmospheric scattering and plant chlorophyll fluorescence,CO2 will be retrieved more accurate.Park Falls station covered with dense plant location in 45.945°N and 90.273°W of Total Carbon Column Observing Network(TCCON)was selected for validation.CO2 retrievals of Greenhouse Gases Observing Satellite(GOSAT)without chlorophyll fluorescence correction are about 2 ppm under bias,which was corrected obviously through the method of this paper,as the largest bias reduces from 2.58 ppm to 1.49 ppm.In the same time,the standard deviations are also improved.From the validation results we can see that the effect of plant chlorophyll fluorescence on CO2 retrieval is corrected effectively.