電離層擾動對VLF電磁波的傳播影響
發(fā)布時間：2018-08-25 18:10
【摘要】：甚低頻(VLF)電磁波在地-電離層波導(dǎo)中傳播具有衰減小、穩(wěn)定性高、傳播距離遠(yuǎn)等優(yōu)點。研究VLF電磁波在電離層中的傳播機理與仿真計算,對進(jìn)一步開展VLF通信、VLF監(jiān)測電離層有重要的理論價值和實際意義。針對VLF電磁波從地面到衛(wèi)星高度的傳播,特別是電離層擾動對VLF傳播特性的影響,本課題進(jìn)行了如下仿真研究。首先基于麥克斯韋方程推導(dǎo)了全波分析法下的VLF傳播模型。通過對色散方程解得的虛部為負(fù)的折射系數(shù)取反,解決了數(shù)值不穩(wěn)定問題。并將輻射源看做由電流密度表示的能量薄層,使得傳播計算能夠引入任意形式的輻射源。進(jìn)行傅里葉變換,將計算引入到波矢量k域,得到全向輻射傳播模型。同時,結(jié)合電離層底部參數(shù)的解析模型與IRI模型、NRLMSISE-00大氣模型計算引入電離層參數(shù),利用IGRF模型引入地磁場參數(shù),建立了從地面到衛(wèi)星高度的VLF傳播全波分析模型。其次,在單向輻射模式下,針對輻射源參數(shù)、地磁場參數(shù)、電離層參數(shù)以及緯度對VLF電磁波傳輸特性的影響進(jìn)行了系統(tǒng)的仿真分析。仿真計算發(fā)現(xiàn),在地-電離層波導(dǎo)當(dāng)中能量幾乎不衰減,在大約60-100km范圍能量衰減迅速,電磁波進(jìn)入E、F層后能量衰減緩慢。夜間傳播衰減明顯低于白天。隨著頻率的升高,反射吸收層上的傳播衰減增大,反射高度升高。傳播衰減并不隨地磁傾角線性變化,VLF電磁波的上行傳播在南半球衰減小于北半球,赤道附近衰減最大。然后,在全向輻射模式下,同樣針對輻射源參數(shù)、地磁場參數(shù)、電離層參數(shù)及緯度進(jìn)行了全面的仿真計算和分析。并將全波法計算結(jié)果和DEMETER衛(wèi)星觀測數(shù)據(jù)對比,驗證了全向輻射模型的正確性。仿真結(jié)果發(fā)現(xiàn),在地-電離層波導(dǎo)當(dāng)中電磁波以波跳形式傳播,能量呈現(xiàn)南北對稱分布。電磁波到達(dá)電離層底部的反射吸收層上時,大部分被反射、吸收,只有較少的部分穿透底部電離層,因此底部電離層上的傳播衰減最顯著。穿透底部電離層的電磁波將順著磁力線方向在電離層中傳播,傳播衰減很小,且受地磁場影響能量呈現(xiàn)南北不對稱分布。最后,考慮到多種空間天氣事件都會對電離層電子密度、中性粒子密度、電子溫度造成擾動,創(chuàng)新性地將這三種電離層擾動分別引入傳播計算,分析了VLF傳輸特性的變化。仿真結(jié)果發(fā)現(xiàn),這三種擾動主要影響VLF在穿透反射吸收層時的衰減,加強性擾動使得衰減增大。
[Abstract]:The propagation of very low frequency (VLF) electromagnetic wave in the ground-ionospheric waveguide has the advantages of low attenuation, high stability and long propagation distance. It is of great theoretical and practical significance to study the propagation mechanism and simulation of VLF electromagnetic wave in ionosphere. Aiming at the propagation of VLF electromagnetic wave from ground to satellite, especially the influence of ionospheric disturbance on the propagation characteristics of VLF, the following simulation research is carried out in this paper. Firstly, the VLF propagation model based on Maxwell equation is derived. The numerical instability problem is solved by inverting the refraction coefficient with negative imaginary part of the solution of the dispersion equation. The radiation source is regarded as a thin layer of energy represented by the current density, so that the propagation calculation can be introduced into the radiation source of any form. Fourier transform is carried out and the calculation is introduced into the wave vector k domain to obtain the omnidirectional radiation propagation model. At the same time, combined with the analytical model of the bottom parameters of the ionosphere and the IRI model, the ionospheric parameters are introduced into the atmospheric model NRLMSISE-00. Using the IGRF model to introduce the geomagnetic field parameters, the full-wave analysis model of VLF propagation from the ground to the satellite is established. Secondly, the effects of radiation source parameters, geomagnetic field parameters, ionospheric parameters and latitudes on the transmission characteristics of VLF electromagnetic waves are analyzed systematically in unidirectional radiation mode. The simulation results show that the energy in the ground-ionospheric waveguide almost does not attenuate. The energy decay is rapid in the range of 60-100km, and the energy decay is slow after the electromagnetic wave enters the EOF layer. The attenuation of nocturnal propagation is lower than that of daytime. With the increase of the frequency, the propagation attenuation and the reflection height on the reflection absorption layer increase. Propagation attenuation does not vary linearly with magnetic dip angle. The attenuation of VLF electromagnetic wave in the southern hemisphere is less than that in the northern hemisphere, and the attenuation near the equator is the largest. Then, in the omnidirectional radiation mode, the emitter parameters, geomagnetic field parameters, ionospheric parameters and latitude are also simulated and analyzed. The validity of the omnidirectional radiation model is verified by comparing the full wave method with the DEMETER satellite observation data. The simulation results show that the electromagnetic wave propagates in the ground-ionospheric waveguide in the form of wave hopping, and the energy is distributed symmetrically in the north and south. When the electromagnetic wave reaches the reflection and absorption layer at the bottom of the ionosphere, most of the waves are reflected and absorbed, and only a few of them penetrate the bottom ionosphere, so the propagation attenuation on the bottom ionosphere is the most significant. The electromagnetic wave passing through the bottom ionosphere will propagate along the direction of the magnetic line in the ionosphere, and the propagation attenuation will be very small, and the energy affected by the geomagnetic field will present an asymmetric distribution from the north to the south. Finally, considering that the ionospheric electron density, neutral particle density and electron temperature will be disturbed by various space weather events, the three ionospheric disturbances are innovatively introduced into the propagation calculation, and the variation of VLF transmission characteristics is analyzed. The simulation results show that these three kinds of disturbances mainly affect the attenuation of VLF when it penetrates the reflective absorption layer, and the enhanced disturbance increases the attenuation.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TN011
本文編號：2203689
[Abstract]:The propagation of very low frequency (VLF) electromagnetic wave in the ground-ionospheric waveguide has the advantages of low attenuation, high stability and long propagation distance. It is of great theoretical and practical significance to study the propagation mechanism and simulation of VLF electromagnetic wave in ionosphere. Aiming at the propagation of VLF electromagnetic wave from ground to satellite, especially the influence of ionospheric disturbance on the propagation characteristics of VLF, the following simulation research is carried out in this paper. Firstly, the VLF propagation model based on Maxwell equation is derived. The numerical instability problem is solved by inverting the refraction coefficient with negative imaginary part of the solution of the dispersion equation. The radiation source is regarded as a thin layer of energy represented by the current density, so that the propagation calculation can be introduced into the radiation source of any form. Fourier transform is carried out and the calculation is introduced into the wave vector k domain to obtain the omnidirectional radiation propagation model. At the same time, combined with the analytical model of the bottom parameters of the ionosphere and the IRI model, the ionospheric parameters are introduced into the atmospheric model NRLMSISE-00. Using the IGRF model to introduce the geomagnetic field parameters, the full-wave analysis model of VLF propagation from the ground to the satellite is established. Secondly, the effects of radiation source parameters, geomagnetic field parameters, ionospheric parameters and latitudes on the transmission characteristics of VLF electromagnetic waves are analyzed systematically in unidirectional radiation mode. The simulation results show that the energy in the ground-ionospheric waveguide almost does not attenuate. The energy decay is rapid in the range of 60-100km, and the energy decay is slow after the electromagnetic wave enters the EOF layer. The attenuation of nocturnal propagation is lower than that of daytime. With the increase of the frequency, the propagation attenuation and the reflection height on the reflection absorption layer increase. Propagation attenuation does not vary linearly with magnetic dip angle. The attenuation of VLF electromagnetic wave in the southern hemisphere is less than that in the northern hemisphere, and the attenuation near the equator is the largest. Then, in the omnidirectional radiation mode, the emitter parameters, geomagnetic field parameters, ionospheric parameters and latitude are also simulated and analyzed. The validity of the omnidirectional radiation model is verified by comparing the full wave method with the DEMETER satellite observation data. The simulation results show that the electromagnetic wave propagates in the ground-ionospheric waveguide in the form of wave hopping, and the energy is distributed symmetrically in the north and south. When the electromagnetic wave reaches the reflection and absorption layer at the bottom of the ionosphere, most of the waves are reflected and absorbed, and only a few of them penetrate the bottom ionosphere, so the propagation attenuation on the bottom ionosphere is the most significant. The electromagnetic wave passing through the bottom ionosphere will propagate along the direction of the magnetic line in the ionosphere, and the propagation attenuation will be very small, and the energy affected by the geomagnetic field will present an asymmetric distribution from the north to the south. Finally, considering that the ionospheric electron density, neutral particle density and electron temperature will be disturbed by various space weather events, the three ionospheric disturbances are innovatively introduced into the propagation calculation, and the variation of VLF transmission characteristics is analyzed. The simulation results show that these three kinds of disturbances mainly affect the attenuation of VLF when it penetrates the reflective absorption layer, and the enhanced disturbance increases the attenuation.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TN011
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