Numerical Analysis Of VIF Wave Propagation In Ground-Ionospheric Waveguide

Very low frequency(VLF)waves are the 3KHz-30 KHz frequency band in the electromagnetic spectrum,and their wavelengths can reach 10 km to 100 km.They are widely used in geological surveys,earthquake prediction,submarine communications,oil mining,and marine navigation.In the scale range formed by the earth 's surface and the atmosphere,the wavelength of VLF is close to this scale,and long-distance communication can be achieved by a waveguide composed of a ground-ionosphere.Therefore,the problem of radio wave propagation in this guided wave structure has become a research field An important subject of radio communication.In this paper,based on the finite-difference time-domain method(FDTD),combined with the IRI ionospheric model and the theoretical research results of the literature written by Pan Weiyan in 2014,a common propagation model of VLF waves is established and the numerical calculation results of the model are analyzed.The details are as follows:(i)The VLF wave mainly propagates along with ground and it is hardly affected by the ionosphere while distance which the wave runs is less than 400 kilometers.The issues of the curvature of the earth surface can be temporarily ignored.We set up the model of VLF wave on the propagation of electromagnetic waves along with the earth surface to analyze the propagation characteristics under the influence of ground fluctuation factors.(ii)Introduced the basic structure and principle of the ionosphere,and the process of establishing the ground-ionosphere waveguide model using the IRI international ionosphere model,and analyzed the propagation characteristics of the VLF wave under the ionosphere.(iii)Study of VLF wave characteristics The earth's own day-night alternation makes the VLF wave pass through the ionosphere at different heights during propagation.The VLF wave is affected by the ionosphere during day and night propagation,and the VLF wave alternates between day and night There is a special case of the downward propagation,that is,the propagation in the day-night interface,so I use the advantages of FDTD to establish some special cases of VLF propagation models in the ground ionospheric waveguide,mainly VLF waves traverse the day-night interface Propagation model,a model where VLF waves propagate along the day-night interface,and analyzes the propagation characteristics of VLF waves.(iv)Consider the actual situation of VLF wave propagation phase correction.In this paper,by studying the propagation characteristics of VLF waves in the above situations,the phase characteristics in the above cases are analyzed.