## 5 Discussion
### Scattering Model  
The most crucial issue is the scattering model for tropocatter. Troposcatter is a combination of three models: turbulence scattering, stable layer reflection, and irregular layer reflection. Turbulence scattering and stable layer reflection have corresponding atmospheric models. However, the model of irregular layer reflection is not yet clear, and we can only provide some conjectures. The theory of irregular layer reflection suggests that these irregular layers, with a large refractive index gradient, are formed by the intersection of cooling and heating air masses. Moreover, strong convection often leads to precipitation. Recently, it has been proposed that large values of reflectivity correspond to large Richardson numbers and small amounts of turbulent mixing [36]. This means that clear-air echoes are affected by strong turbulent mixing and require unmixed air masses to maintain inhomogeneity. Thus, the wildly fluctuating gradient of the refractive index in the source model is more likely caused by the non-uniformity of meteorological elements rather than air convection. Some meteorologists have privately communicated that weather radars located on ships at sea rarely observe clear-air echoes. We consider that the uniform under  
Figure 20: Radar transmission loss (**a**) and theoretical values based on the ITU-R model (**b**), on 7 May 2021, at 15:00 UTC for an elevation angle of 1.45\({}^{\circ}\). The figure also shows the differential reflectivity (**c**). The area surrounded by the black outline is the suspected area of biological activity.  
lying surface of the ocean greatly reduces the non-uniformity of meteorological elements, thereby weakening the intensity of clear-air echoes.  
The recommendations of the ITU-R give various transmission loss parameters for different climatic regions. This map shows that meteorological conditions play an important role in troposcatter. However, the impact of meteorology on tropospheric scattering is too complex to be captured by a single model. For wireless communication, it is crucial to have a thorough understanding of the weather patterns in a specific region before implementing a tropospheric scatter communication system. The use of advanced modeling techniques, such as numerical weather prediction models, can provide more accurate predictions of transmission loss and improve the reliability of communication systems. Continued research and the improvement of tropospheric scatter technology will enable the development of more robust and effective communication systems. For atmospheric science, understanding troposcatter and its models is important for a variety of fields, including meteorology, environmental science, and astronomy. By studying troposcatter, we can gain a better understanding of the properties of the Earth's atmosphere, the way that air mass affects reflection and transmission through the troposphere, and the impact of atmospheric microscale inhomogeneity on weather.  
In this manuscript, we have presented an introduction that explores and confirms the occurrence of tropospheric scattering in the atmosphere. Although numerous issues remain unresolved, it is crucial to acknowledge that these tasks cannot be accomplished overnight. We hope this manuscript can offer a new research direction and enhance awareness among researchers.