Study On Tropospheric Duct OTH Propagation Over Heterogeneous Land Surface

In recent years,with the large-scale construction of TD-LTE networks and explosive growth of 4G users,the phenomenon of long-distance co-channel interference in mobile communication has become a hot issue for domestic and foreign scholars.Starting with the propagation of the over-the-horizon electromagnetic wave,the propagation characteristics of electromagnetic wave over heterogeneous terrain in a complex atmospheric environment is studied.When electromagnetic wave propagating in the troposphere,it is affected not only by the complex land surface,but also by complex atmospheric environment such as tropospheric duct and atmospheric turbulence.On the one hand,the propagation of electromagnetic wave will be cut off by the terrain obstruction,in which there will be a blind spot.On the other hand,the over-the-horizon propagation effects is produced in complex atmospheric environment,which will lead to long-distance co-channel interference in mobile communications and the abnormal operation of mobile systems.Therefore,it is of great practical significance to study the propagation characteristics of electromagnetic wave in a complex atmosphere over a heterogeneous land surface.For heterogeneous land surface,the heterogeneity is manifested as the heterogeneity of land surface media and topography.For complex atmosphere environment,two kinds of abnormal atmospheric structures,including tropospheric duct and atmospheric turbulence,is discussed in this paper.Based on the former,the propagation characteristics of electromagnetic wave in a complex atmospheric environment over the actual surface are studied.Based on the atmospheric refractive index,the model of propagation of electromagnetic wave in the atmospheric duct and the atmospheric turbulence over actual land surface is constructed,surrounded by the geographical environment of parabolic equations.And the propagation characteristics of electromagnetic wave in the troposphere is analyzed,combining the digital map.The specific research results are as follows:The formation mechanism,type and refractive index profile of tropospheric duct are expounded.The parabolic equation theory(PE)and terrain processing methods of propagation of electromagnetic wave in the tropospheric duct is described,which provides theoretical basis for the model construction of propagation of electromagnetic wave mentioned later.The selection of the max cutoff wavelength and trap angle of electromagnetic wave in different types of tropospheric duct is analyzed.The conversion of two digital map formats,including traditional digital map and digital elevation model is achieved numerically.The technology of two-dimensional terrain meshing in DEM is studied and the reading of terrain data in the target area is achieved in this paper,which provides real terrain data for calculating propagation characteristics of electromagnetic wave in the the actual surface.Based on the scattering parabolic equation,the propagation characteristics of electromagnetic wave over the heterogeneous land surface is studied,and the effect of the heterogeneous land surface on propagation characteristics of electromagnetic wave is dicussed.The refractive index profile of the atmospheric duct is introduced to study propagation characteristics in effects of the atmospheric duct,tropospheric scattering and heterogeneous land surface.When the height of the land surface is lower than the height of the duct,the propagation loss of the evaporation duct mainly depends on its trapping effect.Beyond a certain area of propagation,it depends on tropospheric scattering,which is showed in calculation results.For the surface duct,the tropospheric turbulence has a little effect on propagation loss because the trapping effect is much higher than the evaporating duct,leading to that the propagation loss depends mainly on the surface duct.Based on digital maps and parabolic equations,the prediction model of propagation of electromagnetic wave is constructed.Calculation accuracy of PE model is improved by introducing the real terrain information and making the corresponding changes to the relevant electromagnetic parameters of different media on the surface.The effects of different radar parameters,duct parameters,and surface parameters on the propagation characteristics of electromagnetic wave in a single environment are analyzed.The over-the-horizon propagation characteristics of electromagnetic wave in the different types of ducts is calculated numerically on four actual links.