【作者】 佟铁钢；

【导师】 何继善；

【作者基本信息】 中南大学 ， 地球探测与信息技术， 2010， 博士

【摘要】 广域电磁法是何继善院士提出的一种新型高效的人工源频率域电磁测深方法。它使用高效特殊的伪随机多频信号作为场源,一次发送强度大体相当的多个不同频率的激励信号,同时接收多个不同频率的响应,放弃了传统的CSAMT效率低的变频方案和奇次谐波方案,实现一台发送,多台接收。利用电磁场的统一性,测量人工源电磁场的一个分量(电分量或磁分量),而不是同时测量相互正交的E和H,计算电场(或磁场)的全区视电阻率精确表达式。在凡是满足偶极源条件下的广域范围内进行测量并提取电阻率信息,致力于短收发距的测量,或者在同等水平的收发距上增大勘探深度。该方法摆脱了MT法天然场源信号微弱和随机变化的不利因素,在供电时测量总场,克服了TEM测量二次场而需要电流大装备笨重的弱点,提高了野外勘查的速度,扩大了频率域电磁测深应用范围,改善勘查效果,具有非常重要的理论意义和应用价值。本文以伪随机多频信号作为E-Hz广域电磁法的激励场源,详细地论述了场源信号的时间域表达式的编码原则及编码规律,频率域的频谱分析,硬件的实现方法。依据E-Hz广域电磁法的观测方案中使用水平电偶源激励大地,从电磁场基本理论出发,详细地推导了水平电偶源在层状介质空间下的解,分析了水平电偶源在均匀半空间下各种因素影响下场响应特性,利用汉克尔变换对均匀半空间介质下的水平电偶源的电磁场进行了正演数值模拟,并与解析解对比,验证了正演算法的正确性。文中提出了符合视电阻率定义原则的E-Hz广域视电阻率定义,采用逆样条插值方法对均匀半空间的电磁场与电阻率存在的复杂隐函数进行了求取E-Hz广域电磁测深法的视电阻率,完成了不同模型及不同因素影响情况下的视电阻率曲线特征分析,同时,与现有天然场源的测深法和E-Ex广域电磁测深法进行了视电阻率理论曲线的对比和分析,并给出了一种适合野外实际应用的校正垂直磁场的广域电磁测深法E-Hz广域视电阻率的计算方法。随后,提出了广域电磁测深法的自适应反演方法。该方法是建立在Bostick直接反演方法和经典的最小二乘法两者结合的基础上的一种最优化反演方法,利用Bostick直接反演建立初始模型,使用差分方式的无量纲参数解雅可比矩阵。该反演方法能够很好地解决层状介质情况下初始模型层数问题,以及避免由于全区视电阻率表达式是复杂的隐函数关系很难获得偏导数矩阵的解析表达式的问题。最后,通过对现有的频率域测深野外实际装置进行分析,结合新提出E-Hz广域电磁测深法的独特优势,提出了一种新的适合全区域的野外观测装置-E-Hz广域电磁测深法装置。该装置只测量一个垂直方向的磁场Hz分量,在满足偶极源条件下,能够实现全域观测,能够很好地避免了以往由于测量电场而产生的静态效应,同时也不受向传统CSAMT野外装置的测线方向限制,使人工源电磁法变得更加轻便、灵活和高效。更多还原

【Abstract】 Wide-field electromagnetic sounding method is a new and efficient artificial source frequency domain electromagnetic sounding method proposed by He Ji-shan Academician. It uses a high-performance and special pseudo-random multi-frequency signal as the field source to transmit and receive equivalent intensity multi-frequency signals at the same time. In contrast, the method rejects the variable frequency proposal and odd harmonic proposal of the inefficient CSAMT, achieves one transmitter, multiple receivers, uses the uniformity of electromagnetic field to measure one component (electricity component or magnetic component) in the artificial source electromagnetic field but not to measure the mutually perpendicular E and H at the same time. It is an accurate expression of calculating wide-field apparent resistivity in the electric filed (magnetic field), can measure and extract resistivity information in conditions that satisfies the dipole source in vast regions. Furthermore, the method puts emphasis on realizing the measurement of transmitting and receiving in a short distance, or deepening the exploration depth in the same level of transmitting and receiving distance. It shakes off the unfavorable factors such as weak signals, random changes of natural field source in MT method, can measure the total field when power supplies and overcome the weakness of needing high-current large equipment in measuring secondary filed in TEM measurement, so the speed of the ground observation has been greatly increased. The method expands the range of applications in frequency domain electromagnetic sounding, improves the survey results and has a very important theoretical significance and application value.Using pseudo-random multi-frequency signal as E-Hz Wide-field electromagnetic method’s exciting field source, the author has comprehensively demonstrated the field source signals’time domain expression of the coding principles and coding rules, spectral analysis of frequency domain, and hardware implementation. According to the observation program that uses horizontal electric dipole source to excite earth in E-Hz Wide-field electromagnetic sounding method, the paper uses the basic theory of the electromagnetic field, and detailedly deduces the answers to the horizontal electric dipole source in stratified media space, analyzes the field response characteristics of the horizontal electric couple source under the influence of different factors in homogeneous half-space, carries out numerical modeling by using Hankel transform under the homogeneous half-space medium electromagnetic field of horizontal electric dipole and verifies the correctness of the algorithm. The thesis puts forward E-Hz wide-field apparent resistivity which meets the principle of apparent resistivity definition, uses inverse spline interpolation of electromagnetic fields on homogeneous half-space resistivity of the existence of complex and implicit function to calculate E-Hz wide-field sounding method’s apparent resistivity, analyzes the feature of the simulated curves under the influence of different models and different factors. At the same time, comparing the characteristics of the theoretical curve both the present artificial source with electromagnetic sounding methods in natural field source, the author gives E-Hz wide-field apparent resistivity calculation which is fit to the practical application of a vertical magnetic field correction in the wild. Then, the paper proposes an adaptive inversion method that is fit to Wide-domain electromagnetic sounding method. The method is one of the most optimal inversion method based on the combination of Bostick direct inversion principle and the classic least-squares method. It uses Bostick direct inversion principle to establish the initial model, uses dimensionless parametric of differential mode to solve Jacobian matrix. The adaptive inversion method can well solve Layer problem of the initial model for inversion layer in layered media and avoid the problem that it is hard to get Partial derivative matrix of analytical expression for implicit function of wide-field apparent resistivity expression.Finally, by analyzing the existing frequency-domain sounding actual wild configurations, the thesis proposes a new field observations for region-wide configuration----E-Hz Wide-field electromagnetic sounding method configuration. The configuration measures only the vertical component (Hz) of the magnetic field in one direction, meeting dipole source conditions, is able to achieve full-field observation, well avoid the static effect caused by measuring electric field previously, and not subject to restrictions on the direction of survey lines just like traditional CSAMT wild configuration, which makes artificial source electromagnetic method more portable, flexible and efficient.更多还原