Cloud droplet size distribution from 2-D polarization measurements of specMACS during EUREC4A

The data of the two polarization resolving cameras (lower left camera: polLL and lower right camera: polLR) of the spectrometer of the Munich Aerosol Cloud Scanner (specMACS) of the LMU are used to provide a dataset of the cloud droplet size distribution of liquid water clouds. During EUREC4A, specMACS was mounted onboard the research aircraft HALO in a downward-looking perspective. From the polarization measurements of the cloudbow, the effective radius and the effective variance of the cloud droplet size distribution (CDSD) are determined (Pörtge et al., 2023). This dataset provides the CDSDs for individual cloud targets with a target size of approximately 100 m x 100 m for all flight segments flown by HALO during the EUREC4A campaign. As a specific solar and viewing geometry is required to observe the cloudbow, not all flight segments can be evaluated. The effective radii and variances are determined individually for the measurements of all three color channels of the camera. The method derives the CDSD by fitting pre-calculated simulations of the cloudbow to the measurements. Various quality measures (RMSE, quality Index, scaling factor) of the fit are included in the dataset. The polarization signal of the cloudbow is a single scattering signal. Therefore, the derived CDSD should be representative of the CDSD at the cloud top. Furthermore, the mean coordinates of the target are given in both WGS-84 coordinates and in a cartesian reference frame which has its origin at 13.1°N and -57.4°E.本数据集基于慕尼黑大学（LMU）慕尼黑气溶胶云扫描仪（specMACS）光谱仪的两台偏振分辨相机（左下相机：polLL、右下相机：polLR）的观测数据，用于提供液态水云的云滴尺寸分布（cloud droplet size distribution，CDSD）数据集。在EUREC4A实验期间，specMACS被安装在研究飞机HALO上，采用下视观测视角。本数据集通过云弓（cloudbow）的偏振观测数据，反演得到CDSD的有效半径与有效方差（Pörtge等，2023）。本数据集涵盖了EUREC4A实验期间HALO所有飞行航段中，尺寸约为100 m×100 m的单个云体目标的CDSD数据。由于观测云弓需要特定的太阳-观测几何条件，并非所有飞行航段均可用于反演评估。针对相机的全部三个彩色通道的观测数据，将分别反演得到有效半径与有效方差。本数据集采用的反演方法，通过将预先计算的云弓模拟结果与观测数据进行拟合，从而得到CDSD。数据集同时包含了拟合过程的多项质量评估指标，即均方根误差（RMSE，Root Mean Square Error）、质量指数（quality Index）与缩放因子（scaling factor）。云弓的偏振信号属于单次散射信号，因此反演得到的CDSD能够代表云顶处的云滴尺寸分布。此外，云体目标的平均坐标同时采用WGS-84坐标系与原点位于13.1°N、-57.4°E的笛卡尔参考系进行标注。