A cloud‐detection scheme for use with satellite sounding radiances in the context of data assimilation for numerical weather prediction
A cloud‐detection scheme for use with satellite sounding radiances in the context of data assimilation for numerical weather prediction
复制标题
在数值天气预报数据同化背景下与卫星探测辐射一起使用的云检测方案
DOI：
10.1002/qj.49712555902
复制
发表时间：
1999
影响因子：
8.9
通讯作者：
Joe Smith
中科院分区：
文献类型：
--
作者：
S. English;J. Eyre;Joe Smith
描述了一种用于检测云影响的辐射的方案。该方法用于确定无云条件的概率，给出观测结果和我们从数值天气预报（NWP）模式中获得的关于大气的先验知识。这是使用似然方法实现的。它结合了一些替代方法的优点（例如，比较红外和微波通道探测对流层低层，比较红外窗口通道与海面温度），成为一种强大而灵活的方法。它之所以强大，是因为它同时使用不同类型的信息。它是灵活的，因为它不假设正在处理的是哪种仪器，或者什么类型的先验信息（NWP，气候学等）。采用了因此，它可以很容易地扩展到新的情况和数据类型（例如，先进的TIROS操作垂直探测器（ATOVS））。它适用于一般的云检测问题，使用组合微波和红外数据。它已经使用TIROS操作垂直探测器（TOVS）辐射进行了测试。新方法已与专门为TOVS定制的替代云检测方法进行了比较，并已发展到足以用于操作使用的鲁棒性水平。新方法得出的结果与替代方法非常相似，特别是在海洋上空。通过与来自高级甚高分辨率辐射计（AVHRR）的云信息进行比较，研究了确实发生的差异。在处理极低云时，发现替代方法和新方案都有不足之处。新方案识别了现有方案遗漏的一些云。在陆地上，云的探测更加困难。这两种方案往往不一致，但使用AVHRR进行验证也更加困难，因为地表不均匀性增加，发射率和地表温度误差变化更大。因此，新方法被示出为在操作使用中至少与替代方法一样好地执行，同时获得未来系统所需的灵活性。ATOVS的影响进行了讨论。
A scheme for detecting cloud‐affected radiances is described. the method is used to determine the probability of cloud‐free conditions given the observations and the prior knowledge we have about the atmosphere from a numerical weather prediction (NWP) model. This is achieved using a likelihood method. It combines the strengths of some alternative methods (e.g. comparison of infra‐red and microwave channels sounding the lower troposphere and comparison of infra‐red window channels with sea surface temperature) in a powerful and flexible method. It is powerful because it uses different types of information simultaneously. It is flexible because it makes no assumption about which instrument is being processed, or what type of prior information (NWP, climatology etc.) is used. Therefore, it can readily be extended to new situations and data types (e.g. Advanced TIROS Operational Vertical Sounder (ATOVS)). It is suitable for use on general cloud‐detection problems, using combined microwave and infra‐red data. It has been tested using TIROS Operational Vertical Sounder (TOVS) radiances. the new method has been compared with an alternative cloud‐detection method tailored specifically for TOVS and has been developed to a level of robustness adequate for operational use. the new method gave very similar results to the alternative method, especially over the ocean. the differences that did occur have been investigated by comparing with cloud information derived from the Advanced Very High Resolution Radiometer (AVHRR). Both the alternative method and the new scheme were found to have deficiencies when dealing with very low cloud. Some cloud missed by the existing scheme is identified by the new scheme. Over land, cloud detection is more difficult. the two schemes disagree more often, but validation using AVHRR is also more difficult because of increased surface heterogeneity and more variable emissivity and surface temperature errors. the new method is therefore shown to perform at least as well as an alternative method in operational use, whilst gaining the flexibility required for future systems. the implications for ATOVS are discussed.