Effects of the atmospheric refraction on radio line-of-sight distance near the ground in China

In the engineering applications of radio line-of-sight distance, the effective earth radius factor is usually used to characterize the influence of the atmospheric refraction on radio wave propagation. For deeply analyzing the impact of the atmospheric refraction on radio line-of-sight propagation in different regions of China, a radio horizon distance factor is defined in this paper, which can be utilized to characterize the variations of the radio line-of-sight distance relative to the one of standard atmosphere. Based on the atmospheric refractivity gradient data in the lowest 65 m near the ground in China, the statistics of the radio line-of-sight distance factor are obtained in China with the annual and monthly values exceeded for different percentages of time, the characteristics of temporal and spatial variations are analyzed with the data mentioned above and interpolated in the typical area such as Lasa, Chongqing, Xiamen, Bohai Gulf, Xisha and Urumqi. The results show that there are significant temporal and spatial variations of the radio horizon distance factor in different areas of China, which may cause significant temporal and spatial variations of the coverage performance of radio systems. The results are very important for the design and coverage performance evaluation of radio systems used in different areas of China.