Spectral discrimination of coarse and fine mode optical depth
Spectral discrimination of coarse and fine mode optical depth
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DOI：
10.1029/2002jd002975
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发表时间：
2003-09-12
影响因子：
4.4
通讯作者：
Thulasiraman, S
中科院分区：
文献类型：
--
作者：
O'Neill, NT;Eck, TF;Thulasiraman, S
认识到气溶胶粒径分布（PSD）实际上是双峰的，允许从总气溶胶光学深度(tau(a) = tau（f) + tau(c)）的光谱形状中提取细模和粗模光学深度(tau（f)和tau(c)）。这种纯光学技术避免了PSD的中间计算，并产生了与tau(a)的光谱信息含量在复杂性上相称的直接光输出。分离成tau(f)和tau(c)是一个稳健的过程，并产生气溶胶光学统计，这比从tau(a)的一般分析中获得的统计更具有内在性。部分（光学）验证通过(1)证明所采用的简单模型的物理相干性，(2)证明tau(c)变化与薄云事件的摄影证据一致，tau(f)变化与晴空和雾霾事件的摄影证据一致，以及(3)表明，相对于太阳消光和天空辐射数据的组合反演，tau(f)和tau(c)的检索值具有良好的相关性，如果有弱偏差的话。光谱反演技术允许对标准（基于时间的）云筛选算法进行更仔细的检查。据推测，在抽样的病例中，与业务云筛查的被动或主动缺陷相关的月度或长期统计数据的扰动很小，有时是中等的。在这些缺点明显会对具体事件的解释产生重大影响的地方，提供了每日的例证；(1)由于排除了高频细模事件，tau(f)中的调试误差；(2)由于包含了高频不足的薄均质云事件，tau(c)中的遗漏误差。
[1] The recognition that the aerosol particle size distribution (PSD) is effectively bimodal permits the extraction of the fine and coarse mode optical depths (tau(f) and tau(c)) from the spectral shape of the total aerosol optical depth (tau(a) = tau(f) + tau(c)). This purely optical technique avoids intermediate computations of the PSD and yields a direct optical output that is commensurate in complexity with the spectral information content of tau(a). The separation into tau(f) and tau(c) is a robust process and yields aerosol optical statistics, which are more intrinsic than those, obtained from a generic analysis of tau(a). Partial (optical) validation is provided by ( 1) demonstrating the physical coherence of the simple model employed, ( 2) demonstrating that tau(c) variation is coherent with photographic evidence of thin cloud events and that tau(f) variation is coherent with photographic evidence of clear sky and haze events, and ( 3) showing that the retrieved values of tau(f) and tau(c) are well-correlated, if weakly biased, relative to formal inversions of combined solar extinction and sky radiance data. The spectral inversion technique permitted a closer scrutiny of a standard ( temporally based) cloud-screening algorithm. Perturbations of monthly or longer-term statistics associated with passive or active shortcomings of operational cloud screening were inferred to be small to occasionally moderate over a sampling of cases. Diurnal illustrations were given where it was clear that such shortcomings can have a significant impact on the interpretation of specific events; ( 1) commission errors in tau(f) due to the exclusion of excessively high-frequency fine mode events and ( 2) omission errors in tau(c) due to the inclusion of insufficiently high-frequency thin homogeneous cloud events.