Abstract：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.
Key words：Ultraviolet; Rainfall particles; Scattering intensity; T matrix
