短波红外CO_2反演过程约束研究及初步反演结果

CO_2 retrieval and preliminary retrieval results from space-based observations in shortwave infrared band

短波红外通道卫星CO2遥感是近年国际研究热点。首先,开展了卫星观测对气溶胶及大气温度的敏感性研究;其次,针对基于最优化理论的非线性迭代反演方法反演过程中的不收敛问题,提出了修正的阻尼牛顿方法(MDNM),并利用模拟数据评估了MDNM方法的有效性;最后,利用GOSAT卫星数据反演CO2的垂直混合比浓度,并与地基TCCON站点数进行比对。研究结果表明:短波近红外CO2卫星遥感受气溶胶散射及温度影响明显;通过地基比对初步验证了MDNM具有良好的精度,两者的相关性R2达到了0.729。

CO2 is a primary greenhouse gas in the atmosphere and many scientific missions from all over the world are focused on space-based remote sensing of CO2 using shortwave infrared technique. We present an improved method to retrieve CO2 column abundance from space-based observations in a shortwave infrared band. We analyze the sensitivities of CO2 observations to aerosol scattering and atmospheric temperature profiling using the forward model. We also evaluate the reduced accuracy of CO2 retrieval caused by aerosol scattering and 1 K random error of temperature profiles. We propose a Modified Damped Newton Method （MDNM） for CO2 retrieval and present the retrieval samples to evaluate the performance of the proposed algorithm. Sensitivity stud- ies show that the influence of aerosol scattering and temperature on CO2 remote sensing and scattering can cause a misestimate of up to 13.2 ppm of CO2 concentration. We retrieve the CO2 column abundance from GOSAT L1B data using MDNM method, and the results are compared with ground-based measurements from Total Carbon Column Observing Network （TCCON）. The correlation coefficient R-square between the retrieved results and TCCON measurements is 0.729. Sensitivity studies show that aerosol scattering can cause a significant error in CO2 retrieval. A comparison between satellite retrievals and ground-based measurements shows good agreement. The proposed MDNM method is preliminarily proven to accurate.