时间域航空电磁扩散特征和成像深度研究

发布时间：2018-12-17 07:39

【摘要】：为了研究时间域航空电磁系统扩散特征,基于连续性边界条件将电磁场向下延拓得到地下介质中各点处的频率域响应,通过傅里叶变换将其变换到时间域.计算阶跃波形发射时垂直磁偶极子和水平磁偶极子在均匀半空间介质和两层介质中产生的电磁场,通过电流密度矢量图和随时间变化的电流密度等值线展示电磁场在地下介质中的扩散过程.电磁场在地下的扩散受电阻率结构的影响.在良导地区电磁场扩散慢、衰减快,而在高阻地区电磁场扩散快、衰减慢.垂直磁偶极子在地下产生的感应电流形成一个电流环随时间向下、向外扩散.水平磁偶极子在地下产生的感应电流形成两个互相叠加的电流环.时间域电磁场扩散代表着真正物理意义上的电磁扩散,因为它展示了地下电磁场空间分布随时间的变化和场强的衰减.基于对感应电流环的研究,我们探究了扩散深度和时间域航空电磁数据成像深度的关系.时间域电磁场扩散规律的研究不仅加深了对电磁扩散特征的理解,更有助于提高航空电磁数据解释水平.
[Abstract]:In order to study the diffusion characteristics of time-domain aero-electromagnetic system, the electromagnetic field is extended downwards based on the continuous boundary condition to obtain the frequency domain response at each point in the underground medium, which is transformed to the time domain by Fourier transform. The electromagnetic fields produced by vertical magnetic dipole and horizontal magnetic dipole in homogeneous half-space medium and two-layer medium are calculated when the step waveform is emitted. The diffusion process of electromagnetic field in underground medium is demonstrated by current density vector diagram and current density isoline with time. The diffusion of electromagnetic field underground is affected by the resistivity structure. The electromagnetic field diffuses slowly and attenuates rapidly in the good conduction region, while in the high resistance area, the electromagnetic field diffuses quickly and attenuates slowly. The induced current generated by the vertical magnetic dipole in the ground forms a current loop which diffuses outward with time. The induced currents generated by horizontal magnetic dipoles in the ground form two superimposed current loops. The time domain electromagnetic field diffusion represents the real physical electromagnetic diffusion because it shows the change of the spatial distribution of the underground electromagnetic field with time and the attenuation of the field strength. Based on the research of inductive current loop, we investigate the relationship between diffusion depth and time domain airborne electromagnetic data imaging depth. The study of the diffusion law of electromagnetic field in time domain not only deepens the understanding of the characteristics of electromagnetic diffusion, but also helps to improve the interpretation level of aeronautical electromagnetic data.
【作者单位】：吉林大学地球探测科学与技术学院;
【基金】：国家自然科学基金重点项目(41530320)和面上项目(41274121) 国家青年基金项目(41404093) 国家重大科研装备研究项目(ZDYZ2012-1-03,20130523MTEM05)联合资助
【分类号】：P631.326

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