基于人工源的甚低频电磁波空间传播特征统计分析

Statistical analysis of the propagation characteristics of VLF electromagnetic waves excited by the artificial transmitter

利用2005年1月至2010年11月DEMETER卫星记录的NWC发射站的VLF电场功率谱数据,采用指数拟合的方法,分析了VLF电磁波在卫星高度激发的电场空间分布和衰减特征.研究结果表明:(1)VLF电场在发射站上空及其磁共轭区有着很强的对应关系,存在南、北2个强电场中心涡;(2)相对于发射站的位置,VLF电场中心点具有经度和纬度偏移,日侧地磁经度偏移均值大于夜侧,而地磁纬度偏移均值则小于夜侧;(3)日侧VLF电场强度呈现出周期性的年变化;(4)在VLF电场中心10°范围内,电场强度随距离快速衰减,衰减常数b在长达6年的时间内保持稳定.在以上研究结果基础上初步构建的卫星高度人工源电磁波空间分布特征,将为研究地表-电离层电磁波传播机理提供基础技术支撑.

Based on the data collection in VLF electric field power spectral density（PSD）recorded by DEMETER satellite during January 2005 to November 2011,the spatial distribution and attenuation features in electric field at topside ionosphere excited by NWC transmitter has been analyzed by using exponential fitting method.It is found that：（1）The VLF electric field exhibits strong relations in the ionosphere over the transmitter and its magnetic conjugate area,presenting two electric field vortex centers at southern and northern hemisphere respectively;（2）The longitude and latitude of VLF electric field center in ionosphere has an offset to the actual location of the transmitter,in which the averaged longitudinal deviationat dayside is greater than that at nightside,while the latitudinal deviation at dayside is less than that at nightside;（3）The annual periodis revealed in dayside VLF electric field intensity variations;（4）Within 10°scale around the VLF electric field center,the electric field intensity decreases quickly with the increase of distance,and the averaged fitted coefficient b values is steady in six years.Thepreliminary results in the space distribution characteristics at satellite altitude excited by the artificial VLF transmitter will provide basic technical support for the electromagnetic wave propagation mechanism from ground into the ionosphere.