Modeling And Simulation Of Complex Meteorological Environments Based On Parabolic Equation

Millimeter wave technology has been widely used in various fields of defense and civilian, such as communication, radar, guidance, remote sensing, etc. But because of its shorter wavelength, the propagation characteristics of millimeter wave will be easily affected by meteorology environments as it propagates in the troposphere. The effects mainly due to the absorption of atmospheric molecules, raindrops, fogdrops and sandstorm. If there is bad weather such as rain, fog or dust storm, the propagation attenuation caused by atmospheric and bad weather will become serious, which may affect the performance of millimeter wave systems in most cases. So study of the propagation characteristics of millimeter wave in complex meteorology environments is of great significance.Among the present models of tropospheric radio propagation, parabolic equation (PE) method is not only able to take account of wave refraction and diffraction, but also to deal with irregular terrain and complex atmosphere structures synchronously. Furthermore it may obtain electromagnetic data of large area (kilometer level) quickly as solved by the split-step Fourier transform (SSFT) algorithm. Accordingly, the PE method has been extensively used to predict the radio wave propagation in troposphere. This paper is mainly focused on the modeling of complex meteorology environments based on the PE method and investigates the effective permittivities of rain medium, fog medium and sandstorm. Based on theose effective permittivities, a wave propagation model of the PE method is proposed for the use of long-range radio wave propagation with complex geographical and meteorology conditions and it should provide some new ideas for the development of propagation characteristics of millimeter wave. The main works in this paper are as follows:Firstly, the PE method and its SSFT algorithm are introduced. The models of irregular terrain and rough sea surface are set up, respectively. On this basis, a parabolic equation method for calculating the atmospheric attenuation of millimeter wave is proposed. According to the atmosphere pressure, temperature and humidity, complex refractive index model of atmospheric is employed to calculate the refractive index of each step. Revising the refraction term using the refractive index, the atmospheric attenuation along propagation path may be analyzed by PE method. At last the method has been used to model millimeter wave propagation over the rough sea surface with islands.Secondly, the meteorology environments along propagation path such as rain, fog or sandstorm are treated as a mixture comprising of drops and atmospheric. According to polarization theory of dielectrics, this dissertation has studied the model of effective permittivity for mix medium, which is able to take into account physical characteristics of meteorology environments, such as shape, size, temperature, distribution and so on, as well as the effects of depolarization field on particles. The model has been applied to calculate the effective permittivity of sandstorm medium. The relations between the effective permittivity and temperature, visibility, electromagnetic frequency have been given, respectively. Using the effective permittivity, the PE method for calculating sandstorm attenuation of millimeter wave is proposed, and the method has been employed to study the propagation characteristics of millimeter wave in duststorm environment with uniform and non-uniform distribution.Thirdly, the PE method for radio propagation in fog medium has been studied. The PE method is employed to estimate fog attenuation of millimeter wave in complex environments, which has been verified by the Rayleigh approximation and an empirical formula. The fog attenuation with irregular terrain and rough sea surface has been analyzed, respectively. For the case of advection fog and atmospheric duct exist together, the propagation characteristics of millimeter wave in mixed environments formed with advection fog and elevated duct have also been investigated. The results demonstrated that the PE model should be able to simultaneously take into account the atmospheric duct propagation phenomena and fog attenuation of millimeter wave.Fourthly, rain medium is treated as an anisotropy mixture comprising of spherical and ellipsoidal raindrops with different sizes in atmosphere. Taking into account the effects of rain rate, size, distribution, temperature, shape of the rain drops and frequency, polarization of radiowaves on the dielectric property, an analytical formula for the effective permittivity of the rain medium is introduced. And the effects of raindrops reradiation are discussed as their dimensions become comparable to the wavelength. Based on the effective permittivity, the PE model for estimating rain attenuation of millimeter wave in complex environments has been firstly developed via revising the refractive index. The accuracy of our method is fully comparable to that of ITU-R model, and this model is also able to mdeal with multipath propagation which the ITU-R model can not deal with. Meanwhile, based on the above findings, a propagation model including complex geographical environments, such as irregular terrain, rough sea surface, and complex meteorology environments, such as rain, fog, sandstorm, atmospheric duct, has been proposed using the PE method. The model is suitable to simulate long-range millimeter wave propagation with complex geographical and meteorology conditions, which has great reference value for the practical engineering applications.Fifthly, the PE modeling of the electromagnetic pulse propagation has been discussed. the frequency-domain PE is employed to calculate single-frequency signal in the frequence band, and the impacts by those signals which outside the band are ignored, which may significantly improve the computational efficiency. Pulse signal at receive point is obtained via inverse Fourier transform and the selection method of Fourier transform scale is also discussed. A parallel computing program based on OpenMP has been proposed, which may further improve the computational efficiency. Finally, the pulse wave propagation loss in the condition of standard atmosphere, irregular terrain and rough sea surface has been simulated and discussed.