کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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5429608 | 1397362 | 2011 | 10 صفحه PDF | دانلود رایگان |
Lidar ratio (i.e., extinction-to-backscatter ratio) is a key parameter required for retrieving extinction profiles and optical depths from elastic backscatter lidar measurements, and the quality of any extinction retrieval depends critically on the accuracy of the assumed or measured lidar ratio. In this study, we analyze the first two and a half years of the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) data acquired during nighttime. Distributions of the effective lidar ratio (ELR), which is the product of the lidar ratio and an instrument-dependent multiple scattering factor, are derived for opaque dust layers observed by CALIOP over the North Africa. The median and mean ELR values are, respectively, 36.4 and 38.5Â sr at 532Â nm and 47.7 and 50.3Â sr at 1064Â nm. For these opaque dust layers, the derived ELR decreases as the volume depolarization ratio (VDR) increases, reflecting the impact of multiple scattering within the dense layers. The particulate depolarization ratio is typically â¼0.3 at 532Â nm for African dust observed by CALIOP. This ratio can increase to â¼0.4 in the presence of significant multiple scattering. Correspondingly, the calculated ELR will decrease to â¼20Â sr at 532Â nm and to â¼30Â sr at 1064Â nm. The median and mean effective lidar ratio values approach, respectively, to 38 and 40Â sr at 532Â nm and 52 and 55Â sr at 1064Â nm for smaller VDR values measured in less dense layers where the multiple scattering is relatively insignificant. These values are very close to those derived in previous case studies for moderately dense dust. Case studies are also performed to examine the impacts of multiple scattering. The results obtained are generally consistent with Monte-Carlo simulations.
Journal: Journal of Quantitative Spectroscopy and Radiative Transfer - Volume 112, Issue 2, January 2011, Pages 204-213