气溶胶高值区短波红外CO2卫星遥感反演算法研究

Satellite observations of shortwave-infrared(SWIR) band have high sensitivity of CO2 concentration near the surface and can meet the demand of CO2 distribution data both in carbon source and sink searching and climate change research which ground-based observations cannot supply. In contrast, thermal IR techniques have less sensitivity near surface. But observations in SWIR are often disturbed by aerosol scattering, which can lead to significant retrieval error of CO2. It is very essential to develop a method to correct aerosol scattering for CO2 retrieval, especially in China locating in high aerosol optical depth region. Using observations from GOSAT, this study aims to solve the problem of aerosol scattering affect to CO2 retrieval in SWIR band. Thinking it is difficult to acquire aerosol scattering parameters synchronously, we turn to Path length Probability Density Function (PPDF) method based on equivalence theorem that parameterizes aerosol scattering using 4 PPDF factors. With the assistant synchronous observations in O2-A band, we will overcome limitation of the empirical model used in PPDF and develop a new PPDF-based method for CO2 retrieval in SWIR band. Then we will use GOSAT observations in typical region to retrieve CO2 concentration. Validation and error analysis will be carried out by comparing the retrieval results with measurements from ground observing stations and flying flask.

短波红外CO2卫星遥感一方面可以弥补传统的地基站点观测数据稀少的不足，另外也克服了热红外卫星遥感监测对底层大气CO2不敏感的缺点，可以为全球碳的源汇识别和气候变化研究提供数据支持。然而，短波红外卫星遥感观测往往会受到气溶胶等散射的影响，导致CO2遥感精度严重退化。所以，气溶胶散射效应的估算校正对开展短波红外CO2卫星遥感十分重要，特别是对处于气溶胶高值区的中国。本研究将利用当前唯一在轨的温室气体观测卫星GOSAT卫星数据，克服实际观测中难以实时获得视场内气溶胶粒子光学散射参数来校正散射效应的难题，分析研究基于等效理论的光子路径分布概率函数（PPDF）方法，结合GOSAT卫星O2-A通道辅助观测，建立一种不依赖于经验模型参数化估算气溶胶散射效应的短波红外CO2卫星反演算法。课题选择典型示范区的卫星观测资料进行反演试验，并利用地基站点及飞行采样等数据资料对反演结果进行验证与误差分析。

在气候变化与全球变暖的背景下，国际社会围绕温室气体的减排与控制达成了广泛的共识，形成了一系列的排放协议。针对碳排放的评估，需要发展时空连续的精准卫星监测技术。我国作为碳排放大国，在当前污染事件频发的大气背景下，迫切需要主要温室气体（CO2）的卫星高精度遥感监测。项目根据大气中辐射传输过程原理及非线性特征，提出了改进的基于最优化理论的非线性迭代反演模型；综合分析了气溶胶散射对短波太阳辐射传输路径及大气消光效应的影响，定量评估基于等效理论的气溶胶散射效应的参数化因子的敏感性及精度水平，改进原有的经验模型导致的参数化方法的局限，提出了CO2浓度与气溶胶散射参数化因子同步反演方法，构建了适于气溶胶高值区的短波红外CO2卫星遥感反演模型，为在我国大气重污染背景下开展CO2浓度卫星精准监测提供了技术支撑。