# Impact of Weather Factors on Unmanned Aerial Vehicles' Wireless Communications
## 3 Results and Discussion
### Atmospheric Weather Variations
The results indicated a direct relationship between the increased propagation distance and the corresponding increase in signal attenuation, attributable to the combined effects of absorption and scattering phenomena. Absorption and scattering are governed by the wavelength of the incident signal and the size of the raindrops. Depending on the precipitation rate, raindrop diameter ranges from 0.1 to 5 mm. The signal wavelength in the frequency range of 1 to 100 GHz varies from 300 to 3 mm. When the wavelength significantly exceeds the raindrop size, Rayleigh scattering becomes the predominant mode of scattering. However, as the wavelength approaches or becomes comparable to the size of the raindrop, Mie scattering becomes the dominant mode [37; 38]. As illustrated, the attenuation increased at a much faster rate in the lower frequency region, and subsequently slowed down before leveling off in the higher frequency region. This phenomenon is due to the applicability of Rayleigh and Mie scattering in different frequency regions. In the lower frequency region (<10 GHz), due to the wavelength being much larger than the raindrop diameter, Rayleigh scattering is applicable. The intensity of Rayleigh scattered signal exhibits an inverse proportionality to the fourth power of the wavelength. Consequently, increased scattering is observed at shorter wavelengths and the attenuation rises much faster. By contrast, Mie scattering does not demonstrate this pronounced dependence on wavelength reduction. As a result, the attenuation rapidly levels off in the frequency region >10 GHz. Figure 10b illustrates the impact of varying heights, ranging from 100 to 400 m. The rain rate, propagation distance, temperature, and pressure were held constant in this case. The results show a highly consistent attenuation profile across the different heights. This consistency results from relatively unchanged atmospheric conditions and identical path lengths across the considered height range. Figure 10c presents the effect of the precipitation intensity for rain rates of 1, 10, 50, and 120 mm/h, with the other variables held constant, as in the previous cases. As the rainfall intensity increased, there was a corresponding rise in signal attenuation. With the increase in operating frequency, although the attenuation exhibits a steep rise in the lower (<10 GHz) frequency region, the absolute value of attenuation for the highest rain rate (120.0 mm/h) remains under 50 dB. Under the assumed conditions, maximum attenuations for the rain rates of 1.0, 10.0, and 50.0 mm/h in the lower frequency range were approximately 0.1, 1, and 10 dB, respectively. Figure 9: Impact of clouds and fog on signal attenuation across various frequencies: (**a**) shows how attenuation changes for four specific distance measurements; (**b**) illustrates attenuation variations at different altitudes; (**c**) presents the influence of liquid water density fluctuations on attenuation. In this case, the predominance of scattering due to the larger raindrop sizes compared to the smaller particulates associated with clouds/fog leads to a more pronounced increase in attenuation. A comparative analysis of the results for the cases of gas, clouds/fog, and rain demonstrates that, under the specified conditions, high intensity rain produces attenuation exceeding 100 dB in the 1 to 100 GHz operating range, making it the most significant atmospheric weather condition affecting UAV communications. However, for UAV/GCS operating frequencies that are under 10 GHz, the worst-case attenuation for rain approaches 50 dB. While the worst-case attenuations due to gases and clouds/fog are 0.1 dB and 1 dB, respectively. Hence, for reliable communication under all weather conditions, it is imperative that link budgeting be based on the rain-based attenuation as it far exceeds the attenuation caused by atmospheric gases and clouds/fog. Figure 11 shows BER as a function of the carrier frequency under different atmospheric attenuation conditions, gas, cloud/fog, and rain.