基于迁移学习方法的山东冷云冰晶特征分布研究

Distribution of Ice Crystal Characteristics of Cold Cloud in Shandong Province Based on Transfer Learning Method

为分析冷云中冰晶的分布特征,揭示冰晶增长演变机制,根据冰晶形状和尺度特征分为8类并进行标注,同时标注1类隔断栏进行数据质量控制,将9类标签图像整合并建立图像集,利用迁移学习VGGNet16方法进行识别训练,经训练模型分类准确率达98%。将模型应用到秋季冷云冰晶特征研究中,选取3次积层混合云和3次层状云降水过程,分析冰晶形状在不同温度区间的占比及冰晶谱变化特征,结果表明,温度通过影响冰晶基面与棱面的比值来决定冰晶初始形状分布,相同温度区间积层混合云内球状冰晶和线型冰晶占比高于层状云,低于-12℃后各类冰晶占比相对固定;积层混合云内线型冰晶直径集中在300~800μm,冰晶谱呈多峰分布,聚合体直径大于600μm,冰晶谱首尾两端浓度相当,球状冰晶直径集中在120~300μm,冰晶谱呈单调下降趋势。

In order to analyze the distribution characteristics of ice crystals in cold clouds and reveal the evolution mechanism of their growth,ice crystals are classified into 8 categories and labeled according to their shapes and sizes.At the same time,one type of partition column is labeled for data quality control.Then,the 9 types of labeled images are integrated to build an image dataset.The transfer learning VGGNet16 model is adopted for identification training,and the classification accuracy of the trained model reaches 98%.The model is applied to the study of ice crystal characteristics of cold clouds in autumn.Three cumulus-stratiform mixed cloud precipitation processes and three stratiform cloud precipitation processes in 2019 are selected to analyze the proportion of ice crystal shapes in different temperature ranges and the change characteristics of ice crystal size distribution.The results show that the initial shape distribution of ice crystal is determined by the temperature’s affecting the ratio of base surface to edge surface of ice crystals.In the same temperature range,the proportion of spherical ice crystals and linear ice crystals in cumulus-stratiform mixed clouds is higher than that in stratiform cloud,and the proportion of various ice crystals is relatively fixed when the temperature is below-12℃.In cumulus-stratiform mixed clouds,the diameters of linear ice crystals are concentrated in 300-800μm with the ice crystal size distribution being multimodal.The diameters of aggregated ice crystals are greater than 600μm.The concentrations at the beginning and the end of the ice crystal spectrum are equal.The diameters of spherical ice crystals are concentrated in the range of 120-300μm,and the ice crystal size distribution shows a monotonically decreasing trend.