Structural uncertainty in air mass factor calculation for NO2 and HCHO satellite retrievals
Structural uncertainty in air mass factor calculation for NO2 and HCHO satellite retrievals
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DOI：
10.5194/amt-10-759-2017
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发表时间：
2016-11
影响因子：
3.8
通讯作者：
A. Lorente
中科院分区：
文献类型：
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作者：
A. Lorente
大气质量因子（AMF）的计算是最大的不确定性来源NO2和HCHO卫星反演的情况下，在对流层低层的痕量气体浓度增强。如果科学界对相同的卫星观测采用不同的检索方法，就会产生结构上的不确定性。在这里，我们通过详细比较AMF计算方法，从臭氧监测仪器（OMI）的测量七个检索组之间的结构不同，解决AMF结构不确定性的问题。我们估计AMF计算过程的每个子步骤中结构不确定性的升级。这超出了算法的不确定性估计提供了国家的最先进的检索，解决了理论传播的不确定性，一个特定的检索算法。我们发现，四个辐射传输模式（RTMs）（DAK，McArtim，SCIATRAN和VLIDORT）模拟的大气顶部反射率在1.5%以内。我们发现，不同的检索组同意高度分辨AMF的计算从不同的RTMs（在3%以内），并在对流层AMF（在6%以内），只要相同的辅助数据（表面反射率，地形高度，云参数和微量气体轮廓）和云和气溶胶校正程序正在使用。结构的不确定性急剧增加时，检索组使用他们的偏好辅助数据，云和气溶胶校正。平均而言，我们估计AMF结构不确定性在污染区域为42%，在未污染区域为31%，主要是由先验痕量气体剖面、表面散射和云参数的实质性差异驱动的。对一种特定算法的敏感性研究表明，不同的云校正方法导致污染条件下的AMF差异很大（5 - 40%取决于云分数和云压，平均11%），即使是低云分数（<0.2），气溶胶校正的选择在高污染和高气溶胶负载的情况下引入了50%的平均不确定性。我们的工作表明，AMF计算的结构不确定性是显着的，它主要是由假设和选择，以代表大气的状态。为了决定哪种方法和哪些辅助数据是最好的AMF计算，我们呼吁精心设计的验证练习，重点是污染的条件下，AMF结构的不确定性对NO2和HCHO检索的影响最大。
Air mass factor (AMF) calculation is the largest source of uncertainty in NO2 and HCHO satellite retrievals in situations with enhanced trace gas concentrations in the lower troposphere. Structural uncertainty arises when different retrieval methodologies are applied within the scientific community to the same satellite observations. Here, we address the issue of AMF structural uncertainty via a detailed comparison of AMF calculation methods that are structurally different between seven retrieval groups for measurements from the Ozone Monitoring Instrument (OMI). We estimate the escalation of structural uncertainty in every sub-step of the AMF calculation process. This goes beyond the algorithm uncertainty estimates provided in state-of-the-art retrievals, which address the theoretical propagation of uncertainties for one particular retrieval algorithm only. We find that top-of-atmosphere reflectances simulated by four radiative transfer models (RTMs) (DAK, McArtim, SCIATRAN and VLIDORT) agree within 1.5 %. We find that different retrieval groups agree well in the calculations of altitude resolved AMFs from different RTMs (to within 3 %), and in the tropospheric AMFs (to within 6 %) as long as identical ancillary data (surface albedo, terrain height, cloud parameters and trace gas profile) and cloud and aerosol correction procedures are being used. Structural uncertainty increases sharply when retrieval groups use their preference for ancillary data, cloud and aerosol correction. On average, we estimate the AMF structural uncertainty to be 42 % over polluted regions and 31 % over unpolluted regions, mostly driven by substantial differences in the a priori trace gas profiles, surface albedo and cloud parameters. Sensitivity studies for one particular algorithm indicate that different cloud correction approaches result in substantial AMF differences in polluted conditions (5 to 40 % depending on cloud fraction and cloud pressure, and 11 % on average) even for low cloud fractions (<0.2) and the choice of aerosol correction introduces an average uncertainty of 50 % for situations with high pollution and high aerosol loading. Our work shows that structural uncertainty in AMF calculations is significant and that it is mainly caused by the assumptions and choices made to represent the state of the atmosphere. In order to decide which approach and which ancillary data are best for AMF calculations, we call for well-designed validation exercises focusing on polluted conditions in which AMF structural uncertainty has the highest impact on NO2 and HCHO retrievals.