VLF电波渗透到卫星高度电离层传播的全波计算
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摘要
考虑斜向地磁场的影响将电离层设为多层水平分层各向异性有耗介质,利用传播矩阵法求解全波方程,进而研究分析VLF频段电离层反射系数随电波频率的变化,电离层中两种特征极化波的折射和极化特性,两特征波的电磁场水平分量以及坡印廷能流密度随传播高度的变化.数值计算结果表明,地-电离层波导中的垂直极化波比平行极化波易渗透进入电离层;电离层中两种特征极化波可分为左旋和右旋圆极化波,左旋分支由于D层强吸收作用表现为速衰减模,而右旋分支表现为可传播模,在传播过程中电磁波的能量主要存储在磁场中;电波频率越低,其在电离层中的传播损耗越小.由数值模拟结果发现,卫星监测VLF频段的低频部分及更低频段的水平磁场变化对于发现地震电离层电磁前兆异常可能更为有效.
Obvious anomalous VLF,ULF,SLF signals related with earthquake have been recorded by satellites.Research on finding electromagnetic anomaly in the ionosphere may become an important way for earthquake prediction.The calculation of VLF wave propagating in the ionosphere can provide theoretical results for extracting abnormal signals related with earthquake from satellite observation data.The ionosphere has been set to be lossy and anisotropic horizontal multi-layer media.The propagation matrix method had been used to solve the full wave equation.The reflection and polarization coefficient of two characteristic waves in the ionosphere has been calculated.The poynting flux and horizontal components of electromagnetic fields varying with altitude have also been simulated.The numerical results show that it is easier for the vertical polarized wave to penetrate into the ionosphere than parallel polarized wave.The left-handed polarization wave suffers severe attenuation in D region for the strong absorption.The right-handed polarization wave is transmitting mode,and the wave energy is saved in the magnetic field.The attenuation of the wave is lower when the frequency is smaller which means it may be more efficient for us to study the magnetic field of the lower frequency wave to find the electromagnetic abnormals of earthquakes.
Obvious anomalous VLF,ULF,SLF signals related with earthquake have been recorded by satellites.Research on finding electromagnetic anomaly in the ionosphere may become an important way for earthquake prediction.The calculation of VLF wave propagating in the ionosphere can provide theoretical results for extracting abnormal signals related with earthquake from satellite observation data.The ionosphere has been set to be lossy and anisotropic horizontal multi-layer media.The propagation matrix method had been used to solve the full wave equation.The reflection and polarization coefficient of two characteristic waves in the ionosphere has been calculated.The poynting flux and horizontal components of electromagnetic fields varying with altitude have also been simulated.The numerical results show that it is easier for the vertical polarized wave to penetrate into the ionosphere than parallel polarized wave.The left-handed polarization wave suffers severe attenuation in D region for the strong absorption.The right-handed polarization wave is transmitting mode,and the wave energy is saved in the magnetic field.The attenuation of the wave is lower when the frequency is smaller which means it may be more efficient for us to study the magnetic field of the lower frequency wave to find the electromagnetic abnormals of earthquakes.
引文
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[16]Helliwell R A.Whistlers and Related Ionospheric Phenomena[M].Calif:Stanford University Press,1965:63-76
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[18]Weiyan Pan.LF VLF ELF Wave Propagation[M].Chengdu:University of Electronic Science and Technology Press,2004:254-255.In Chinese(潘威炎.长波超长波极长波传播[M].成都:电子科技大学出版社,2004:254-255)
[19]Leiphart J P,Zeek R W,Bearce L S,et al.Penetration of the Ionosphere by Very-Low-Frequency Radio Signals Interim Results of the LOFTI I Experiment[J].Proc.IRE,1962,50,1,doi:10.1109/JRPROC.1962.288269
[20]Shufan Zhao,Xuhui Shen,Weiyan Pan,Xuemin Zhang and Li Liao.Penetration characteristics of VLF wave from atmosphere into lower ionosphere[J].Earthquake Sci.,23(3):275-281
[2]Freund F T,Takeuchi A,Lau B W S,et al.Stressinduced changes in the electrical conductivity of igneous rocks and the generation of ground currents[J].Terr.Atmos.Ocean.Sci.,2004,15(3):437-468
[3]Parrot M.Statistical study of ELF/VLF emissions recorded by a low altitude satellite during seismic events[J].J.Geophys.Res.,1994,99,A12,doi:10.1029/94JA0207223
[4]Henderson T R,Sonwalkar V S,Helliwell R,et al.A search for ELF/VLF emissions induced by earthquakes as observed in the ionosphere by the DE 2 satellite[J].J.Geophys.Res.,1993,98,A6,doi:10.1029/92JA01533
[5]Serebryakova O N,Bilichenko S V,Chmyrev V M,et al.Electromagnetic ELF radiation from earthquake regions as observed by low-altitude satellites[J].Geophys.Res.Lett.,1992,19,2,doi:10.1029/91GL02775
[6]Molchanov O A,Hayakawa M,Rafalsky V A.Penetration characteristics of electromagnetic emissions from an underground seismic source into the atmosphere,ionosphere,and magnetosphere[J].J.Geophys.Res.,1995,100,A2,doi:10.1029/94JA02524
[7]Bortnik J,Bleier T.Full wave calculation of the source characteristics of seismogenic electromagnetic signals as observed at LEO satellite altitudes[J].Eos.Trans.AGU,2004,85(47):T51B-0453
[8]Ozaki M,Yagitani S,Nagano I,et al.Ionospheric penetration characteristics of ELF waves radiated from a current source in the lithosphere related to seismic activity[J].Radio Sci.,2009,44,RS1005,doi:10.1029/2008RS003927
[9]Yeh K C and Liu C H.Theory of Ionospheric Waves[M].New York:Academic Press,1972
[10]Budden K G.Radio Waves in the Ionosphere.London:Cambridge University Press,1961:389-390
[11]Chew W C.Waves and Field in Inhomogeneous Media[M].New York:Van Nostrand Reinhold,1990:109-114
[12]Kunz K S.Numerical Analysis[M].New York:McGrawHill,1957:236-238
[13]Nagano I,Mambo M,Hutatsuishi G.Numerical calculation of electromagnetic waves in an isotropic multilayered medium[J].Radio Sci.,1975,10,6,doi:10.1029/RS010-i006p00611
[14]Bilitza D.International reference ionosphere 2000[J].Radio Sci.,2001,36,2,doi:10.1029/2000RS002432
[15]Cummer S A.Modeling electromagnetic propagation in the Earth-ionosphere waveguide[J].IEEE Trans.Ant.Prop.,2000,48,9,doi:10.1109/8.898776
[16]Helliwell R A.Whistlers and Related Ionospheric Phenomena[M].Calif:Stanford University Press,1965:63-76
[17]Barton C E.International Geomagnetic Reference Field:the seventh generation[J].J.Geomagn.Geoelec,1997,49:123-148
[18]Weiyan Pan.LF VLF ELF Wave Propagation[M].Chengdu:University of Electronic Science and Technology Press,2004:254-255.In Chinese(潘威炎.长波超长波极长波传播[M].成都:电子科技大学出版社,2004:254-255)
[19]Leiphart J P,Zeek R W,Bearce L S,et al.Penetration of the Ionosphere by Very-Low-Frequency Radio Signals Interim Results of the LOFTI I Experiment[J].Proc.IRE,1962,50,1,doi:10.1109/JRPROC.1962.288269
[20]Shufan Zhao,Xuhui Shen,Weiyan Pan,Xuemin Zhang and Li Liao.Penetration characteristics of VLF wave from atmosphere into lower ionosphere[J].Earthquake Sci.,23(3):275-281
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