Study on the Scattering Effect of Terahertz Waves in Near-Surface Atmosphere

Terahertz waves suffer from scattering attenuation of various types of particles due to the complex environment in the near-surface atmosphere. This paper focused on the scattering attenuation of terahertz waves due to different kinds of particles, including droplets, haze particles, and raindrops. The optical parameters of these particles were determined by meteorological data and the related literature. The characteristics of the scattering attenuation of terahertz waves on hazy days were analyzed using Rayleigh scattering and the lognormal distribution of particles, based on different levels of pollution and frequency. The basic physical characteristics of fog were also examined to determine the influence of water content on the visibility and size distribution of droplets. The scattering characteristics of terahertz waves caused by advection fog and radiation fog were assessed using the Mie scattering theory based on the complex index of droplet refraction. Then, the characteristics of scattering attenuation in fog days were identified under different levels of visibility. The Rayleigh approximation method was used to numerically model the scattering effect of small droplets and the effect of temperature and visibility on characteristic attenuation. Results show that, by comparing the distribution of different raindrop sizes, the Joss distribution was found to be quite accurate. Raindrop size distribution and scattering attenuation characteristics under different rainfall rates were identified using the Mie scattering method. The meteorological environment is complex in the near-earth atmosphere and the scattering attenuation of terahertz waves under fog, hazy, and rainy conditions cannot be ignored. Meteorological factors, such as visibility and rainfall rate, exert critical influences on the scattering attenuation characteristics of terahertz waves.