# Impact of Weather Factors on Unmanned Aerial Vehicles' Wireless Communications
## 3 Results and Discussion
### Atmospheric Weather Variations
The liquid water density, height, temperature, and pressure were held constant at 10 g/m\({}^{3}\), 400 m, 25 \({}^{\circ}\)C, and 1013.25 hPa, respectively. As this figure shows, there was a noticeable increase in the attenuation of the signal as the propagation distance increased. The attenuation rose at a faster rate for frequencies under 22 GHz. Beyond this value, this rate significantly decreased. This phenomenon is attributed to the inverse relationship between frequency and wavelength, wherein higher frequencies correspond to shorter wavelengths relative to the dimensions of water droplets. Shortening of the wavelength with respect to the dimension of the water droplets results in the reduction of the scattering effect as a limiting value of the scattering coefficient. Additionally, for frequencies higher than 25 GHz, the resonant absorption by water molecules rapidly diminishes. Figure 9b shows the impact of the UAV height on attenuation, considering heights of 100, 200, 300, and 400 m. The water vapor density, propagation distance, temperature, and pressure were maintained at 10 g/m\({}^{3}\), 2000 m, 15 \({}^{\circ}\)C, and 1013.25 hPa, respectively. In this instance, minimal changes in the atmospheric parameters across the assumed heights, coupled with a constant path length for all the four height values, resulted in closely matched attenuation profiles. Figure 9c illustrates the effect of liquid water vapor density variations on signal attenuation. The other parameters, propagation distance, height, temperature, and pressure, were maintained constant at 2000 m, 400 m, 15 \({}^{\circ}\)C, and 1013.25 hPa, respectively. A  
corresponding increase in attenuation was observed as the water vapor density increased, in accordance with the expected result. Notably, no attenuation spike was observed for frequencies under 22 GHz band in the cloud/fog-based attenuation, as was observed in the atmospheric gas-based attenuation. This phenomenon is attributed to the larger size of the suspended water droplets resulting from the clustering of water molecules in clouds and fog due to condensation. Clustering of water molecules results in distinctive changes in the attenuation characteristics. Scattering, owing to suspended water droplets, becomes the dominant phenomenon in the ensuing attenuation [36]. Therefore, as most UAV command control systems currently operate at frequencies below 10 GHz, the maximum attenuation observed is approximately 1 dB. This attenuation is significantly lower compared to free-space path loss. Our findings also indicate that even the most severe cloud and fog conditions will result in only minimal increases in attenuation. Figure 10 displays the results corresponding to the effect of rain on the signal attenuation over the assumed frequency range. The simulations were methodically parameterized with defined values for the critical variables: propagation distance, elevation, rain rate, ambient temperature, and atmospheric pressure. Figure 10a provides a graphical representation of signal attenuation as influenced by carrier frequency across various propagation distances (500, 1000, 1500, and 2000 m). The conditions were standardized with a rain rate of 120 mm/h, an elevation of 400 m, a temperature of 25 \({}^{\circ}\)C, and an atmospheric pressure of 1013.25 hPa. Given the frequent occurrences of severe weather conditions all over the world, we selected a maximum value of rain rate  
Figure 8: Effect of atmospheric gases on signal attenuation across various frequencies: (**a**) demonstrates the variation in attenuation for four specific distance measurements; (**b**) illustrates attenuation variations at different altitudes; (**c**) presents the influence of water vapor density variations on attenuation; (**d**) depicts the effect of variations in temperature. (120 mm/h, recorded in various parts of the world), to assess the maximum impact due to rain under extreme weather conditions.