大气CO2反演的地表反射率影响分析与比值反演方法

近红外波段空基大气CO₂反演是一个病态问题，地表特征的不确定性是其重要的影响因素之一。针对大气CO₂高精度反演的需求，研究了地表反射率两大不确定性因素对大气CO₂反演的影响程度，提出了比值光谱法对这种影响进行校正。比值光谱法中CO₂无吸收通道(off-line)的选择至关重要，通过比较和分析多种off-line通道的选择方法，发现多通道多点平均法因多数据平均可降低随机误差的优势，获得的off-line通道对应的反演精度最高，而且离散程度也小。比值光谱法结合多通道多点平均法选取出的off-line通道对地表反射率的不确定性影响有明显的校正效果，有利于大气CO₂反演精度的提高。

Study of the Effect of Surface Reflectance on Atmospheric CO2 Retrieval and Ratio Spectrometry

Retrieving atmospheric CO₂ concentration from space-based infrared measurements is an ill-posed problem, and the uncertainty of ground properties is an important impacting factor. For the requirement of high precision retrieval of atmospheric CO₂, the effects of surface reflectance must be corrected. Thus a surface reflectance correction method is proposed. In this correction method, the selection of non-CO₂ absorption (off-line) channel is an important part, so several different types of off-line channels were compared and analyzed. We finally found that averaging all data of multi-channels as off-line channel is the best way, in which the retrieval precision is highest and dispersion is lowest, because the advantage is that averaging many data can reduce random error. The effects of surface reflectance on CO₂ retrieval decreased significantly after correction using ratio spectrometry combined with the selected off-line channel, and CO₂ retrieval precision improved greatly.