降雨粒子的无线紫外光散射特性

紫外光与降雨粒子相互作用发生散射，散射光特性改变能够反映降雨粒子的相关物理特性（如粒子尺寸参数、浓度、形态），因此研究粒子的物理参数对散射光特性的影响对有效提高光谱法定量探测降水的精度有很大意义。由于雨滴在非球形降水粒子中具有代表性，以群雨滴粒子为例，采用T矩阵理论，利用紫外光直视和非直视单次散射模型，分析了入射光波长、群雨滴粒子形态、降雨强度、粒径大小与散射光强之间的关系。并用蒙特卡洛方法仿真分析了非球形群雨滴粒子在不同降雨强度和粒径下散射角与散射光强之间的关系，以及降雨环境中的风切变对紫外光散射特性的影响。通过理论及仿真分析，得到了不同群雨滴粒子形态下的路径损耗，不同降雨强度、风切变率和粒径下的散射光强分布。仿真结果表明：在紫外光直视与非直视通信方式下，降雨环境中的通信质量比晴天条件下的通信质量差，即路径损耗增大。当粒径分布已知时，随着降雨强度的增大，衰减系数增大，路径损耗增加，且直视通信方式的路径损耗比非直视降低7 dB左右。随着降雨强度、风切变率和粒子粒径的增大，散射光强曲线整体呈下降趋势，其中，降雨强度的变化对散射光强分布影响程度最大。相同通信距离时，不同降雨强度下的紫外光散射光强分布均随着散射角的增大而减小，当散射角继续增大到90°时，有效散射体体积逐渐减小，接收到的光子能量减小，暴雨中的散射光强衰减程度最大。相同降雨强度下考虑风切变时，相比较无风时的路径损耗增大5 dB左右。除此之外，还研究了椭球形和切比雪夫形粒子对紫外光散射光强的影响，结果表明当粒子粒径分布相同时，椭球形粒子的散射光强衰减较广义切比雪夫形粒子大。根据散射粒子的散射光强分布以及路径损耗能够区分雨滴粒子是否由相同粒径及形态组成，为粒子测量提供理论基础。分析降水中群雨滴粒子的光散射特性，为提高光谱法评估降水衰减的数值模拟方面提供理论依据，为光学技术在探测识别降水现象等气象领域的广泛应用提供了设计参考。

Research on Wireless Ultraviolet Scattering Characteristics of Rainfall Particles

As ultraviolet light will be scattered by rainfall particles, the changes of scattered light characteristics can reflect the physical properties (such as particle size parameters, density and shape ) of rainfall particles. Therefore, it is of great significance to study the influence of the physical parameters of the particles on the characteristics of the scattered light that can effectively improve the accuracy of the detection of precipitation by spectroscopy. Due to the representation of raindrops in non-spherical precipitation particles, in this paper, the raindrop particles are taken as an example. Using the UV line-of-sight and non-line-of-sight scattering models, we analyzed the relationship between the scattered light intensity and a series of object parameters, including wavelength of incident light, the morphology of raindrop particles, rainfall intensity and particle size. For non-spherical raindrop particles, we also simulated and analyzed the relationship between scattering angle and scattered light intensity at different particle size, rainfall intensity and the influence of wind shear in rainfall on ultraviolet light scattering properties using Monte Carlo method. Through theoretical and simulation analysis, the path loss under different groups of raindrop particle shapes, the scattered light intensity distribution under different rainfall intensity, wind shear rate and particle size were obtained. The simulation results show that the communication quality in the rainfall environment is worse than that in the sunny day, which means greater path loss under UV LOS and NLOS communication. When the particle size distribution is known with the increase of rainfall intensity, attenuation coefficient increase and the path loss increase, the attenuation of LOS communication can be less than about 7 dB for NLOS communication. With the increase of rainfall intensity, wind shear rate and particle size, scattered light intensity curve shows a downward trend, among which, the change in rainfall intensity has the greatest effect on the scattered light intensity. When the communication distance is the same, the intensity distribution of UV light scattering under different rainfall intensity decreases with the increase of scattering angle, when the scattering angle increases by more than 90 degrees, the effective scattering volume decreases, the received photon energy decreases, so the scattering intensity in rainstorm attenuation is larger. Under the same rainfall intensity, when the wind shear is taken into account, the scattering intensity decreases, and the path loss increases about 5 dB when compared with that without wind. In addition, the effects of ellipsoid and Chebyshev particles on the intensity of UV light scattering have also been studied in this paper, which show that when the particle size is the same, the attenuation of ellipsoid particles is larger than that of Chebyshev particles. The scattered light intensity distribution and path loss of the scattering particles can be used to distinguish whether the raindrop particles are composed of the same particle size and morphology, providing a theoretical basis for particle measurement. And we analyzed the characteristics of light scattering of raindrop particles in rainfall, which provides a theoretical basis for improving the numerical simulation of rainfall attenuation assessment by spectroscopy and also provides a design reference for the wide application of optical technology in the detection and identification of rainfall phenomena and other meteorological fields.