Effect Of Ionospheric Disturbance On The Propagation Of VLF Electromagnetic Wave

The propagation of very low frequency(VLF)electromagnetic waves in the Earthionospheric waveguides has the advantages of low attenuation,high stability and far propagation distance.It is of great theoretical and practical significance to study the propagation mechanism and simulation of VLF electromagnetic wave in ionosphere for further development of VLF communication and VLF monitoring of ionospheric.Aiming at the VLF electromagnetic wave propagation from the ground to the satellite altitude path,especially the ionospheric disturbance on the propagation characteristics of VLF,the following simulation was carried out.Firstly,the VLF propagation model under full-wave analysis was deduced based on the Maxwell equation.The problem of numerical instability was solved by reversing the refraction coefficient which was solved by the dispersion equation and having negative imaginary part.By treating the radiation source as an energy thin layer represented by a current density,the propagation calculation could be introduced into any form of radiation source.Then through the Fourier transform,the calculation was introduced into the wave vector k domain,so the omnidirectional radiation propagation model was obtained.At the same time,the ionospheric parameters were calculated by using the analytical model of bottom ionospheric parameters,the IRI model and the NRLMSISE-00 atmospheric model.The geomagnetic field parameters were introduced by IGRF model.A full-wave analysis model of VLF propagation from the ground to the satellite height was established.Secondly,in the unidirectional radiation mode,the influence of radiation source parameters,geomagnetic field parameters,ionospheric parameters and latitude on the transmission characteristics of VLF electromagnetic waves was simulated systematically.The simulation results showed that the energy was hardly attenuated in the groundionospheric waveguide,and the energy decayed rapidly in the range of about 60-100 km,and the energy decayed slowly after the electromagnetic wave enters the E and F layers.Nighttime attenuation was significantly lower than during the day.The increase in frequency resulted in an increase in the propagation attenuation on the reflective absorber layer,and caused the reflection height to rise.The propagation attenuation did not vary linearly with the magnetic dip angle.The upward propagation attenuation of the VLF electromagnetic wave was smaller in the southern hemisphere than in the northern hemisphere,and the attenuation near the equator was greatest.In addition,in the omnidirectional radiation mode,the VLF transmission characteristics were simulated comprehensively and analyzed for different radiation source parameters,geomagnetic field parameters,ionospheric parameters and latitude.And the results of the full-wave method were compared with the DEMETER satellite observation data so that the correctness of the omnidirectional radiation model was verified.The simulation results showed that in the Earth-ionospheric waveguide,the electromagnetic waves propagated as wave jump and the energy was north-south symmetrical.When the electromagnetic wave reached the reflective absorber layer on the bottom of the ionosphere,most of it was reflected and absorbed,and only a few parts penetrated the bottom ionosphere,so that the propagation attenuation on the bottom ionosphere was most significant.Electromagnetic waves penetrating the bottom ionosphere propagated in the ionosphere in a specific direction,with little attenuation in propagation and an asymmetric distribution of north and south due to geomagnetic field effects.Finally,considering the various spatial weather events can cause the ionospheric disturbances of electron density,neutral particle density and electron temperature,introducing the three kinds of ionospheric disturbances into the propagation calculation innovatively,the simulation calculation was carried out,and the changes in VLF transmission characteristics were analyzed.The simulation results showed that these three kinds of disturbances mainly affected the attenuation of VLF when penetrating the reflective absorption layer.The enhanced disturbance caused the attenuation to increase.