实测1～100kHz大地电磁场分析

Measured magnetotelluric field in 1～100kHz frequency band

通过实例分析实测1~100kHz的大地电磁场的幅度、相互正交的电场和磁场相位差、相关度等数据信息,表明当电磁场信号幅值较大且较平稳时,相应的相互正交的电场与磁场的相位差也较平稳,二者相关度也较高,表明相位差的平稳性和相关度高低能反映信噪比高低;根据近十年实测的中国范围内100个地区的1~100kHz频段大地电磁场数据,统计分析了不同频率电磁场平均值、最小值和最大值,并用最小二乘法拟合最大值、最小值包络线以及平均值曲线,结果表明：天然大地电磁场频谱随频率变化趋势具有规律性,幅值对数和频率对数可采用5次多项式经验公式表征;天然大地电磁场频谱曲线形态基本一致,幅值在一定范围内浮动;在20~30kHz及50~70kHz频段常出现信号极值.最后,长沙月亮岛一个固定测点上十二个月的实测数据表明实测天然大地电磁场频谱呈现季节性差异,特别是4~14kHz频段的电磁场,夏季明显强于冬季.

The measured magnetotelluric field in 1~100kHz frequency band has been studied.The amplitude spectrum of electric field（E）and magnetic field（H）,and the phase difference spectrum,coherency spectrum between the crossed E and H were analyzed.In the frequency band where the amplitudes spectrum of the crossed E and H are both larger,the phase difference spectrum curve is always smoother,and also the coherency is higher.Such correlation may be used to reflect the signal noise ratio. The maximum,average,minimum amplitude spectrum curves of the measured E and H are fitted from the measured data of 100 places.It shows that the E,H amplitude spectrum curve forms in different places are similar,with amplitude in a range.The E field changes more than the H filed as the difference of underground medium affect E much more.It reveals that the signal noise ratio is regularly higher in 5~30kHz frequency band,and there are extremisms in 20~30kHz and 50~70kHz frequently,caused by VLF or LF communication waves.Measured data at one site on the Moon-island in 12 months indicate the seasonal difference of the magnetotelluric field in 1~100 kHz frequency band;it is stronger in summer than in winter,especially in the 4~14kHz frequency.