26 November 2018 San Rafael HailPixel Survey Data and Analysis

The following collection is used to demonstrate the HailPixel survey technique as part of an AGU GRL publication. The following is an abstract for this paper: A new technique, named "HailPixel," is introduced for measuring the maximum dimension and intermediate dimension of hailstones from aerial imagery. The photogrammetry procedure applies a convolutional neural network for robust detection of hailstones against complex backgrounds and an edge detection method for measuring the shape of identified hailstones. This semi-automated technique is capable of measuring many thousands of hailstones within a single survey, which is several orders of magnitude larger than population sizes from existing sensors (e.g., a hail pad). Comparison with a co-located hail pad for an Argentinan hailstorm event demonstrates the larger population size of the HailPixel survey significantly improves the shape and tails of the observed hail size distribution. When hailfall is sparse, such as during large and giant hail events, the large survey area of this technique is especially advantageous for resolving the hail size distribution. The dataset contains the DEM and orthomosaic imagery, processing reports, final location of hail centroids, final measurements of hail major and minor axis, subset offsets and hail pad data. For more information applying the subset offsets to calculate the true position of the hail centroids please see the paper.本数据集用于演示隶属于美国地球物理联盟（American Geophysical Union, AGU）《地球物理研究快报》（Geophysical Research Letters, GRL）一篇发表论文的HailPixel调查技术。以下为该论文的摘要： 本文提出了一种名为‘冰雹像素（HailPixel）’的新技术，用于从航空影像中测量冰雹的最大尺寸与中间尺寸。该摄影测量流程采用卷积神经网络（Convolutional Neural Network, CNN）在复杂背景下实现冰雹的稳健检测，并通过边缘检测方法对已识别冰雹的形状进行量化测量。该半自动化技术可在单次调查中完成数千颗冰雹的尺寸测量，其样本量较现有传感器（如冰雹垫（hail pad））的采集规模高出数个数量级。通过与阿根廷一次冰雹事件中同址布设的冰雹垫进行对比，结果表明HailPixel调查更大的样本量显著优化了观测到的冰雹尺寸分布的形态与尾部特征。在冰雹降落较为稀疏的场景下（如大型乃至巨型冰雹事件），该技术覆盖的大范围调查区域对于精准解析冰雹尺寸分布具有显著优势。 本数据集包含数字高程模型（Digital Elevation Model, DEM）、正射影像（orthomosaic）、处理报告、冰雹质心最终位置、冰雹长轴与短轴的最终测量值、子集偏移量以及冰雹垫数据。如需了解关于利用子集偏移量计算冰雹质心真实位置的更多细节，请参阅该论文。