散射模型和有效粒子半径对卷云光学厚度反演的影响

Influence of Scattering Model and Effective Particle Radius on Cirrus Cloud Optical Thickness Retrieval

为研究不同散射模型和有效粒子半径对卷云光学厚度反演的影响,计算了不同光学厚度下,一般种类混合模型(GHM)、实心柱状模型(SC)和聚合物实心柱状模型(ASC)取不同有效粒子半径时的反射率。理论分析了不同散射模型及其不同有效粒子半径对卷云光学厚度反演结果的影响。使用基于倍加累加法的矢量辐射传输模型RT3计算3种模型卷云光学厚度查找表,基于POLDER数据,采用查找表法进行卷云光学厚度反演实验,实验结果与理论分析一致。结果可知:采用不同散射模型反演得到的卷云光学厚度存在较大差异,相比GHM和SC模型,ASC模型卷云光学厚度反演结果更接近POLDER产品;有效粒子半径越大,光学厚度反演结果越大,GHM和SC的增幅较大,而ASC增幅很小。因此,在不具备有效粒子半径反演能力时,建议采用ASC模型反演卷云光学厚度,以减小有效粒子半径变化对反演结果的影响。上述研究对我国GF-5卫星的卷云光学厚度反演的散射模型选取及反演结果评价具有参考价值。

In order to investigate the influence of different scattering models and effective particle radii on the cirrus cloud optical thickness retrieval,we simulate the reflectance of different effective radii based on General Habit Mixture（GHM）,Solid Column（SC）and Aggregates of Solid Column（ASC）under different cirrus cloud optical thicknesses.The influence of different scattering models and effective radii on the retrieval results of the cirrus cloud optical thickness is theoretically analyzed.The cirrus cloud optical thickness look-up tables of GHM,SC and ASC are calculated by radiative transfer model RT3 based on vector doubling-adding method.The cirrus cloud optical thickness is retrieved by the look-up table method based on the POLDER data.It is found that the retrieval results are consistent with the theoretical analysis.The theoretical analysis and retrieval results show that,for different models,the cirrus cloud optical thickness retrieval results are obviously different.Compared with the GHM and SC models,the retrieval results of cirrus cloud optical thickness by the ASC model are closer to POLDER products.In addition,for these models,the retrieval results of the cirrus cloud optical thickness increase with the increase of effective radius.The results of the ASC model are no obvious increase with the increase of the effective radius,and the results of the GHM and SC models increase greatly with the increase of effective radius.Therefore,when the instrument lacks the ability to retrieve the effective radius,it is suggested that the ASC model can be used to retrieve the cirrus cloud optical thickness,so as to reduce the influence of the effective particle radius variation onthe retrieval results.This study can help to develop cirrus cloud optical thickness algorithms for GF-5 satellite in China.