Synergetic use of POLDER and MODIS for multilayered cloud identification
Synergetic use of POLDER and MODIS for multilayered cloud identification
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协同使用 POLDER 和 MODIS 进行多层云识别
DOI：
10.1016/j.rse.2010.03.014
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发表时间：
2010-09
影响因子：
13.5
通讯作者：
Fan, Xuehua
中科院分区：
文献类型：
--
作者：
Zhao, Zengliang;Yao, Zhigang;Lin, Longfu;Han, Zhigang;Fan, Xuehua
这项研究的目的是研究通过联合使用POLDER-3(地球反射的偏振和方向性)和MODIS(中分辨率成像光谱仪)数据来识别覆盖在低层水云上的包含薄卷云的重叠云的可能性。当薄卷云与液态云层重叠时，可以通过POLDER观测获得液体信息，并可以从MODIS CO2切片技术推断卷云的存在。对东亚一景的POLDER云相和MODIS云顶气压的初步比较也表明，POLDER-3宣布为液态水云的很大一部分云对应于MODIS得到的较低的云顶气压。因此，本文提出了一种基于多层云存在的叠加云识别方法，该方法假设围堰云相为液态水，且MODIS云顶气压小于500hPa.对于所研究的场景，将多层云识别结果与CloudSat和CALIOP(Cloud-Aerosol Lidar with Orthogonal Poly)观测结果进行了比较，结果表明，当上层卷云的可见光学厚度小于2.0时，该方法可以检测到多层云。然后将识别结果与MODIS云多层旗帜进行比较。结果表明，随着MODIS多层云的置信度从最低到最高的增加，多层云与MODIS-OPERATOR算法的一致性从40%以上逐渐提高到近100%。进一步的分析表明，大多数被该方法错误地归类为单层云的多层云可能对应于覆盖较低层水云的相对较厚的卷云。此外，利用这两种方法的多层云探测差异提出了一个指数，以提供覆盖低层水云的卷云光学厚度的一些信息。最后，通过主动测量，将定量比较扩展到不同位置的其他四个场景。结果还表明，两种方法探测到的多层云高层云的平均可见光厚度(1.57)明显小于MODIS运算方法的平均可见光厚度(2.84)，这表明两种方法的结果差异主要是由于对高层云可见光厚度的敏感性不同造成的，可以用来指示覆盖低层水云的卷云的可见光厚度的范围。
The purpose of this study is to investigate the possibility of identifying overlapping clouds that contain thin cirrus overlying a lower-level water cloud by synergetic use of POLDER-3 (Polarization and Directionality of the Earth Reflectance) and MODIS (MODerate resolution Imaging Spectroradiometer) data. When thin cirrus clouds overlap the liquid cloud layer, the liquid information may be obtained by POLDER observations and the presence of the cirrus may be inferred from the MODIS CO2-slicing technique. An initial comparison of the POLDER cloud phase and the MODIS cloud-top pressure for one scene over East Asia also shows that a large portion of clouds declared as liquid water clouds by POLDER-3 correspond to the lower cloud-top pressures derived from MODIS. As a result, an overlapped cloud identification method is proposed under the assumption that the multilayered cloud would be present if the POLDER cloud phase is liquid water and the MODIS cloud-top pressure is less than 500hPa. For the studied scene, the comparison of the multilayered cloud identification results with CloudSat and CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) observations illustrates that the proposed method could detect multilayered clouds when the upper cirrus has a visible optical thickness of less than 2.0. Then the identification results are compared with the MODIS Cloud_Multi_Layer_Flag. It is indicated that the consistency between the multilayered clouds from the proposed synergy and MODIS-operational algorithm increases gradually from over 40% to nearly 100% with the increase of the confidence level of the MODIS multilayered clouds from the lowest to the highest. Further analysis suggests that the majority of multilayered clouds falsely classified as single-layered clouds by the proposed method may correspond to relatively thick cirrus covering lower-level water clouds. Additionally, an index by using the multilayered cloud detection differences from the two methods is proposed to provide some information on the optical thickness of the cirrus covering lower-level water cloud. Finally, quantitative comparisons are extended to four other scenes at different locations by using active measurements. The results also show that the mean visible optical thickness of the high-level clouds of the multilayered clouds detected by both methods (1.57) is remarkably less than that by only MODIS-operational method (2.84), which means that the differences between the results from the two methods are mainly caused by the different sensitivities to the visible optical thickness of the high-level cloud and could be used to indicate the range of the visible optical thickness of the cirrus clouds covering the lower-level water clouds.
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影响因子：
6.3
作者：
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通讯作者：
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影响因子：
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影响因子：
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通讯作者：
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