Abstract We have analyzed the effect of aerosols on the retrieval of the dry air mixing ratio of carbon dioxide (XCO2) in the Earth's atmosphere from instruments like OCO-2 and GOSAT. High-fidelity simulations of multi-angle spectropolarimetric observations in the O2 A-band and the weak and strong CO2 bands are used to evaluate the information contained in different measurement subsets/synergies for the retrieval of aerosol, surface, and molecular parameters. We contrast the biases and uncertainties in the retrieved XCO2 resulting from the assumption of free or fixed aerosol microphysical parameters in the retrieval algorithm. It is very difficult to achieve the required retrieval accuracy of 0.2% for XCO2 using intensity-only Nadir mode measurements. The uncertainty in the retrieved XCO2 can be minimized by introducing multiangle and polarimetric measurement synergies. While the retrieval bias on XCO2 is practically eliminated by the addition of measurement synergies for free aerosol microphysical parameters, fixed aerosol retrievals can lead to an increase in XCO2 bias. In both cases, our full multi-angle polarimetric dataset produces a maximum uncertainty of ~1.6% in the retrieved XCO2 at low aerosol optical thicknesses and over dark surfaces. The XCO2 retrieval uncertainty improves to better than 0.2% at greater aerosol optical thickness and brighter surfaces. The problematic low aerosol optical thickness and low surface brightness regime produces an XCO2 bias of 1 − 8 % for fixed aerosol microphysics, while the free parameters produce a maximum bias well under 10−3% for all retrieval scenes considered.

中文翻译：

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OCO-2/GOSAT 反演 XCO2 中的气溶胶：信息内容和误差分析

摘要 我们通过OCO-2 和GOSAT 等仪器分析了气溶胶对地球大气中二氧化碳(XCO2) 干空气混合比反演的影响。O2 A 波段和弱和强 CO2 波段的多角度光谱偏振观测的高保真模拟用于评估不同测量子集/协同效应中包含的信息，以检索气溶胶、表面和分子参数。我们对比了在检索算法中假设自由或固定气溶胶微物理参数导致的检索 XCO2 的偏差和不确定性。使用仅强度的天底模式测量很难达到所需的 0.2% 的 XCO2 反演精度。通过引入多角度和极化测量协同作用，可以最大限度地减少检索到的 XCO2 的不确定性。虽然通过增加游离气溶胶微物理参数的测量协同作用实际上消除了 XCO2 的反演偏差，但固定的气溶胶反演会导致 XCO2 偏差的增加。在这两种情况下，我们的完整多角度偏振数据集在低气溶胶光学厚度和黑暗表面上检索到的 XCO2 中产生的最大不确定性约为 1.6%。在更大的气溶胶光学厚度和更亮的表面上，XCO2 反演不确定性提高到优于 0.2%。有问题的低气溶胶光学厚度和低表面亮度状态对固定气溶胶微物理产生 1 - 8 % 的 XCO2 偏差，