基于多角度偏振信息反演海洋上空卷云云顶高度

采用偏振辐射信息反演云顶高度时,为了减小由云层及地表偏振辐射特性变化带来的反演结果不确定度,使用490 nm和865 nm通道多角度偏振信息反演卷云云顶高度.理论分析大气顶偏振特征,给出490 nm与865 nm通道偏振特性差异,说明使用此两通道偏振反射率差反演云顶高度的可行性.假设卷云为一般种类混合模型(General Habit Mixture,GHM),使用倍加累加矢量辐射传输模型计算和分析大气顶490 nm和865 nm通道偏振反射率差对卷云有效粒子半径、光学厚度和云顶压强的敏感性.分析表明,当卷云光学厚度大于3时,偏振反射率差对有效粒子半径和光学厚度的变化不敏感,对云顶压强变化敏感.根据敏感性分析结果选择适当的参数构建偏振反射率差查找表,使用查找表方法反演POLDER3数据的卷云云顶高度,并与POLDER3产品和MODIS产品进行比较.结果表明,与POLDER3的官方算法相比,使用偏振反射率差查找表方法有更宽的散射角适用范围,反演结果与MODIS产品有更好的一致性.

Retrieval of cirrus cloud top height over ocean based on multi-angle polarized information

Cloud top height could be retrieved by polarized information. In order to reduce the uncertainty of retrieval results caused by the variability of cloud and surface polarized properties, the multi-angle polarized information of 490 nm band and 865 nm band w as used to retrieve cirrus cloud top height.Atmospheric top polarized information and the differences of atmospheric top polarized information betw een 490 nm band and 865 nm band w as theoretically analyzed, w hich show ed that it w as feasible to retrieve cirrus cloud top height using polarized reflectance difference betw een 490 nm band and 865 nm band. Cirrus cloud w as assumed as General Habit M ixture ( GHM) model, the polarized reflectance difference w as evaluated by the vector radiative transfer model based on adding-doubling method, and the sensitivity of polarized reflectance to cirrus cloud effective radius, optical thickness and cloud top pressure w ere evaluated. The results show that w hen the cirrus cloud optical thickness is greater than 3, the polarized reflectance difference is not sensitive to the change of effective particle radius and optical thickness, and is sensitive to the change of cloud top pressure. The polarized reflectance difference look-up table w as constructed by choosing appropriate parameters according to sensitivity analysis, and retrieved cirrus cloud top heights using look-up table method base on POLDER3 data. The retrieval results w ere compared w ith POLDER3 product and M ODIS product. The results indicate that compared w ith the official POLDER3 algorithm, the polarized reflectance difference look-up table method could applied to a w ider scattering angle range, and had a better consistency w ith M ODIS product.