基于粒子成像测速技术的雨滴微物理特性研究

Research on microphysical property of raindrops based on particle imaging velocimetry technology

为了获取自然环境条件下的雨滴形状、尺度、速度、取向等微物理特性,基于粒子成像测速的瞬态测量可视化技术,研究基于点扩散函数的图像复原算法和自相关图像的速度提取算法,设计并研制了一种基于面阵电荷耦合元件的自然降水成像测速系统.通过外场观测试验研究了雨滴的直径、速度、轴比和空间取向及其谱分布等微观物理特性;雨滴的速度随直径的增大呈指数增大,轴比随直径的增大呈线性减小,空间取向易受环境风的影响,倾斜角的平均值在2.1?左右,标准偏差为11.5?;基于实测数据拟合了雨滴速度和轴比随直径的变化关系.与国外已有模型相比,本文进一步得出了具有本地化特征的雨滴微物理特性.所得到的结论对于云降水物理学研究、天气雷达地面定标、雨致微波衰减评估等方面的应用具有重要的意义.

In order to obtain the shapes, sizes, fall velocities, orientations of raindrops in the natural condition, starting from the particle imaging velocimetry transient visual measurement technology, an image restoration algorithm based on point spread function and a velocity calculation algorithm based on auto-correlation image are investigated, and a natural precipitation imaging velocimetry system based on a CCD sensor is designed and developed in this paper. The diameters, terminal velocities, axis ratios, orientations and their distributions of raindrops are investigated by the field experiment. The velocities of raindrops increase exponentially with the diameter, and axis ratios of raindrops decrease linearly with the diameter, the orientations of raindrops are easily affected by the wind, the average canting angle for all drops tends to be nearly symmetric 2.1？ with a standard deviation of 11.5？. The empirical relations between velocity and diameter, between axis ratio and diameter are fitted by nonlinear fitting and linear fitting of observed data. In this paper we further provide microphysical characteristics of raindrops with local features. compared with those from the existing model. These conclusions are of important significance for the research on cloud precipitation physics, ground calibration of weather radar, assessment of rain induced microwave attenuation, etc.