Influence Of Coherent Acoustic Waves-induced Disturbance On Radio Propagation Characteristics Of Atmospheric Duct

Atmospheric duct is an important propagation environment for radio systems and play an important role in the performance of radio systems.The main idea of coherent acoustic waves-induced disturbance to the atmospheric duct is that the radio propagation environment is no longer regarded as changing with the nature,but can be artificially controlled.Its application must be based on the study of the atmospheric duct so as to achieve the ultimate goal accurately according to the requirements of the radio system,which provides an effective way for the adjustment of the performance of the radio system involving the atmospheric duct,such as solving the interference caused by the atmospheric duct in 5G,theoretically verifying that the over-the-horizon detection radar stealth technology can be implemented,etc.In this thesis,atmospheric duct and its radio propagation characteristics under coherent Acoustic waves-induced disturbance are studied.The main work is as follows:The genesis of atmospheric duct and its influence on electromagnetic wave propagation are discussed.Firstly,based on Debye theory,the origin of the semi-empirical formula of atmospheric refraction index and its variation with the changes in parameters such as temperature,pressure and water pressure are stated.Secondly,the reasons for the formation of evaporation duct,surface duct,surface-based duct,and elevated duct are analyzed.The propagation trajectories of electromagnetic waves in the standard atmosphere,four atmospheric ducts,and composite duct are simulated.At last,it is concluded that other types of ducts,except evaporation duct,have obvious jumping areas.The accuracy of six kinds of evaporation duct diagnosis models in spatial and temporal dimensions is studied,and the appearance probability of the global atmospheric duct and the statistical distribution of its characteristic parameters are analyzed.Firstly,evaporation duct diagnostic models including LKB,NPS,RSHMU,NWA,and NRL developed based on MOST theory are summarized.Secondly,using global weather data provided by ECMWF,the six models were analyzed and compared from two dimensions,the global scope and the full year span,which reveals the applicability differences of models in different sea areas and at different times.Finally,the model with higher overall accuracy is given.Meanwhile,based on the definition of the characteristic parameters of the atmospheric duct,using the trapped layer data provided by ECMWF in 2019,the appearance probability,top height,thickness and strength of the four types of ducts worldwide are calculated during the year,which draws a conclusion of the distribution rules of each characteristic quantity.The influence of controllable coherent acoustic waves on the refractive index of the atmosphere is studied.Firstly,based on sound wave superposition principle and the principle of phased array,the expression of the sound pressure at a certain point in space generated by a sound source array composed of spherical sound sources is derived.Secondly,the sound pressure is related to the change of the atmospheric refractivity.And then,the influence of different parameters of acoustic array on the atmospheric refractivity is discussed.Finally,the experiment designed proves that coherent acoustic wave can produce pressure fluctuation and affect the propagation of radio wave in the atmosphere.The radio wave propagation loss of the atmospheric duct under the coherent acoustic waves-induced disturbance is studied.Firstly,the advantages and theories of parabolic equation are explained.Secondly,with the combination of mechanism of coherent acoustic waves changing the atmospheric refractivity,the spatial distribution of radio wave propagation loss difference between evaporating duct,surface duct,and surface-based duct is simulated with or without coherent acoustic waves-induced disturbance.Finally,the law of the loss difference distribution when the acoustic array with different parameters interferes with the duct is summarized.The results of this thesis provide basic principle and fundamental experimental verification for the propagation environment for radio systems involving atmospheric duct,and have important scientific significance and potential practical value.