Sensitivity of depolarized lidar signals to cloud and aerosol particle properties

Measurements from depolarized lidars provide a promising method to retrieve both cloud and aerosol properties and a versatile complement to passive satellite-based sensors. For lidar observations of clouds and aerosols, multiple scattering plays an important role in the scattering process. Monte Carlo simulations are carried out to investigate the sensitivity of lidar backscattering depolarization to cloud and aerosol properties. Lidar parameters are chosen to be similar to those of the upcoming space-based CALIPSO lidar. Cases are considered that consist of a single cloud or aerosol layer, as well as a case in which cirrus clouds overlay different types of aerosols. It is demonstrated that besides thermodynamic cloud phase, the depolarized lidar signal may provide additional information on ice or aerosol particle shapes. However, our results show little sensitivity to ice or aerosol particle sizes. Additionally, for the case of multiple but overlapping layers involving both clouds and aerosols, the depolarized lidar contains information that can help identify the particle properties of each layer.     

Comparison of CALIPSO and ground-based lidar profiles over Chung-Li, Taiwan

We report the first inter-comparison of vertical profiles of aerosols and clouds derived from space (CALIPSO) and ground based lidar over Chung-Li, Taiwan. Results show that inter-comparison is closer in case of aerosols than clouds. The strength/shortcoming of the comparison has been also discussed. An iterative calculation to retrieve extinction-to-backscatter ratio (lidar ratio) by using sun-photometer and CALIPSO data is also documented. By using the mentioned method, a mean lidar ratio of 23.5±8.2 sr was found. The derived lidar ratios are lower than former studies. The possible reasons for the difference have been discussed in this paper. The discussed methodology will be helpful to reduce the uncertainty of optical parameters derived from lidar data especially near the surface where the atmosphere is inhomogeneous.     

大气云层分布的偏振激光后向散射研究

 利用大气激光后向散射垂直剖面图与消偏振度相结合的方法,分析CALIPSO卫星偏振激光雷达的后向散射信号。以2008年11月23日和24日的CALIPSO卫星数据为例,研究了北京地区大气中云层在可见光和红外光波段的垂直和水平分布特征。利用交互式数据语言IDL(interactive data language)得到大气后向散射强度的垂直分布及其消偏振度,根据垂直剖面图可以直观地观测大气中各成分（如气溶胶、低空云和卷云等）的空间分布情况,并且能清楚地显示大气边界层的高度,由消偏振度可准确获得云层的分布高度及厚度。观测数据的处理结果表明：在海拔高度3 km~7 km存在厚度为2 km~2.5 km的云,其消偏振度约为0.2。     

基于江西地区多卫星数据的气溶胶立体分布研究

利用长时间序列（2007~2014年）的MODIS/Terra数据探讨了江西地区气溶胶光学厚度（aerosol optical depth, AOD）空间变化特征,发现该地区平均AOD呈现由南往北逐渐递增的趋势,其中,九江和南昌达到最高。同时,利用CALIPSO/CALIOP 垂直特征掩膜获得了气溶胶层与云层的混合和分离状态,计算了气溶胶、不同子类型气溶胶和云的垂直概率分布和最大似然高度（maximum probability height, MPH）。结果表明：气溶胶主要聚集在1~3.5 km,气溶胶层和云层混合状态出现的概率高于分离状态。在2～4 km之间,春季污染沙尘出现的概率最高,冬季次之,夏季与秋季相当,而烟尘气溶胶夏季出现的概率最高,春、冬季相当,秋季次之。基于夜间CALIOP数据计算得到的气溶胶和云的MPH均表现出较大的季节差异性。     

联合星载毫米波雷达和激光雷达资料的云相态识别技术

依据星载偏振激光雷达云相态识别原理,借鉴星载毫米波雷达温度阈值云相态识别方法,利用支持向量机(SVM)构建了联合CloudSat和CALIPSO卫星资料的云相态识别模型并进行了实例反演验证.SVM方法训练和测试样本集采用了CloudSat的2B-GEOPROF-LIDAR云廓线数据、CALIPSO的2级1km云层数据以...     

南京地区气溶胶散射特性综合观测

利用中国气象局南京综合观测基地的Rayleigh-Raman-Mie激光雷达Mie通道实测数据反演分析南京北郊气溶胶光学消光特性。对2013年11月至12月雾霾天气进行观测并分析得到光学消光系数,并结合CALIPSO卫星搭载的激光雷达CALIOPSO level.2分类产品数据进行消光特性参数分析。利用CALIPSO监测2012年冬季一次沙尘过程所得结果与地基微脉冲偏振激光雷达结果一致。     

基于星载激光雷达的AOD与海面风速关系研究

海面上空气溶胶的产生和传输在一定程度上和风有关,研究气溶胶和风速间的关系,对增加大气模式的预测精度有重要意义。文中使用CALIPSO卫星CALIOP激光雷达L2（V3.01）气溶胶层与云层数据,与准同步AQUA卫星的AMSR-E海面风速数据,采用2007年和2008年的1月、4月、7月、10月共8个月的观测数据,研究波长为532 nm的气溶胶光学厚度（AOD）与海面风速间的关系及其随季节、年份的变化。结果显示,无云条件下,全球海洋上空AOD与风速存在关系：当风速在0-12 m/s时,AOD随风速增大而增加,当风速在4-12 m/s时,AOD与风速近似线性关系,当风速>14 m/s时,AOD趋于平稳。     

激光雷达数据应用于海气界面气体传输速率的估算

选取2007年1、4、7、10月4个月夜间无云的云-气溶胶激光雷达和红外探测者观测卫星(CALIPSO)星载激光雷达Version 3.01数据,提取532nm激光海面后向散射系数并计算海面波浪均方斜率。同时选用准同步AMSR-E海面风速数据,利用Wanninkhof等于2009年提出的包含线性、平方、立方项的海面风速与气体传输速率混合关系模型计算海水施密特数为660时的海气界面气体传输速率k660。通过回归分析,得到由星载激光雷达数据反演k660的关系模型。将激光雷达数据反演结果与采用4种典型海面风速关系模型的计算结果进行比较,给出由星载激光雷达数据反演的4个月平均的海气界面气体传输速率全球分布图和纬度分布图。研究表明,CALIPSO星载激光雷达532nm单脉冲测量数据可用于反演海气界面气体传输速率。     

利用CALIPSO卫星数据对大气气溶胶的去偏振度特性分析研究

应用CALIPSO(Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation)卫星数据,对大气中的气溶胶等目标进行了去偏振度计算及分析.结果表明,目标后向散射去偏振度信息,能够很好表征大气气溶胶的构成种类、目标特征、垂直高度分布等特性.气溶胶的去偏振特性,为大气气溶胶的特性与分布情况等研究提供了新的方法与定量化参考参数.CALIPSO数据研究方法和结果,对全球气候变化原因、大气污染、沙尘暴等研究有重要的参考价值.     

Comparison of aerosol characteristics during haze periods over two urban agglomerations in China using CALIPSO observations

Using CALIPSO (cloud-aerosol lidar and infrared pathfinder satellite observation) vertical observation data during haze periods from January 2007 to December 2008, we analyzed differences in aerosol characteristics near the surface, as well as in the middle troposphere between the Beijing–Tianjin–Hebei metropolitan region (Area A) and the Yangtze River Delta region (Area B) in China. One significant difference was that haze pollution in Area A was related to local and non-local aerosols, while in Area B it was related to local anthropogenic sources. In all seasons apart from autumn, aerosol pollution in Area A was more severe than in Area B, both near the surface and at higher altitudes. In Area A, non-spherical aerosols were dominant from 0 to 4 km in spring, summer, and winter; while in autumn, there were considerably high numbers of non-spherical aerosols below 0.5 km, and near-spherical aerosols from 0.5 to 4 km. In Area B, both near-spherical and non-spherical aerosols were common in all seasons. Moreover, aerosols with attenuated color ratios of 0–0.2 were more common in all seasons in Area A than in Area B, indicating that fine particle pollution in Area A was more serious than in Area B. Finally, relatively large aerosols linked to gravity settling appeared more frequently near the surface in Area A than in Area B.