层状介质航空电磁激电效应正反演研究

发布时间：2018-05-28 06:56

本文选题：时间域航空电磁 + 激电效应　；参考：《吉林大学》2017年硕士论文

【摘要】：航空瞬变电磁法(Airborne transient electromagnetic,简称ATEM)凭借其速度快、成本低和便捷高效,能够完成传统地面电磁法难以完成的地形条件复杂、气候环境恶劣地区的资源和环境勘查工作。目前,航空瞬变电磁法在国内外均有较大的发展,特别是近几十年来随着航空瞬变电磁系统的发展和数据采集精度的提高,地球物理工作者经常在晚期时间道航空瞬变电磁响应中发现符号反转现象,经过学者们的研究发现,认为该现象是由于激发极化效应引起的。然而,传统的电阻率反演方法无法对该类航空瞬变电磁数据进行有效地处理解释和正确地反演。早期研究过程中通常直接将符号反转部分的数据直接剔除,仅处理解释早期正响应部分数据,该方法必然导致深部地球物理信息丢失和电阻率反演结果的失真。近几年,关于航空瞬变电磁激电参数的反演已成为航空电磁法的研究热点之一,有效地解决该问题对于航空电磁法的发展和国民经济的增长具有双重意义。本文主要研究内容为层状介质航空瞬变电磁激电效应的正反演。本文首先介绍激发极化法的电化学理论,展示两种典型的激发极化模型。另外,引入目前被广泛使用的Cole-Cole模型,对其进行适当的变换,给出几种典型岩矿石的激电参数取值范围,分析岩矿石电导率的频率特性。这些为后续的研究奠定了理论基础。接着本文研究航空瞬变电磁激电效应对电磁扩散的影响,给出全空间层状模型任意位置的频率域电场分量,根据欧姆定律得到频率域电流密度响应,通过对Cole-Cole模型的分解又可以得到频率域感应电流密度和频率域极化电流密度;利用正余弦变换可以将频率域电流密度转换为时间域电流密度。通过分析感应电流密度、极化电流密度和总电流密度的时间域变化特征,研究极化介质中电磁扩散特征,并研究分析感应电流和极化电流的充放电过程,合理解释极化介质出现符号反转现象。通过研究不同充电率和电导率极化模型中的电磁扩散特征,得出不同激电参数对电磁扩散的影响,进一步加深对航空瞬变电磁激电效应的认识。为后续章节的正演模拟研究提供理论基础。针对航空瞬变电磁激电响应正演模拟,本文以水平圆形回线源为例,给出层状极化模型在水平圆形回线中心处垂直磁场表达式,利用正余弦变换计算航空瞬变电磁激电效应的阶跃响应和脉冲响应,通过卷积技术计算得到任意波形的航空瞬变电磁激电响应,研究分析不同激电参数对航空瞬变电磁激电响应的影响。通过对层状极化模型的正演模拟研究,合理地解释航空瞬变电磁响应中出现多次符号反转的现象。最后本文对航空瞬变电磁激电参数的反演进行研究,采用经典的Occam反演方法,首先介绍Occam反演方法的基本理论,反演过程中对Cole-Cole模型参数进行合理的范围约束,提高了反演的稳定性,也一定程度上降低了反演的多解性。通过对几种典型理论层状极化模型的反演研究,给出本文反演算法的优点及其局限性。综合本文研究成果可为今后的三维航空瞬变电磁激电效应正反演研究工作奠定良好的基础,同时也对进一步认识航空瞬变电磁法中激电效应提供帮助,具有一定的理论研究意义。
[Abstract]:Airborne transient electromagnetic (ATEM), with its fast speed, low cost and convenient and efficient, can complete the complex terrain conditions that the traditional ground electromagnetic method is difficult to complete, and the resources and environmental exploration in poor climate and environment. In the last few decades, with the development of the aeronautical transient electromagnetic system and the improvement of the precision of data acquisition, geophysics often found the phenomenon of sign reversal in the transient electromagnetic response of the late time channel. After the study of the scholars, it was found that the phenomenon was caused by the excitation polarization effect. However, the traditional resistivity inverse was found. The method can not effectively deal with the interpretation and correct inversion of this kind of aero transient electromagnetic data. In the early research process, the data of the reverse part of the symbol are directly eliminated and only the early positive response of the data is explained. This method will inevitably lead to the loss of the physical information in the deep earth and the distortion of the resistivity inversion results. In recent years, the inversion of the parameters of the aero transient electromagnetic excitation has become one of the hot topics in the aero electromagnetic method. The effective solution to the problem is of double significance to the development of the aero electromagnetic method and the growth of the national economy. The main research content of this paper is the positive inversion of the transient electromagnetic excitation effect of layered medium. The first part is the introduction of this paper. The electrochemistry theory of the excitation polarization method shows two typical excitation polarization models. In addition, the Cole-Cole model, which is widely used, is introduced, and the range of the parameter value of several typical rock ores is given and the frequency characteristics of the electrical conductivity of rock ore are analyzed. These have laid a theoretical foundation for the follow-up study. In this paper, the influence of the aeronautical transient electromagnetic excitation effect on the electromagnetic diffusion is studied. The frequency domain electric field component of any space layered model is given. The frequency domain current density response is obtained according to Ohm's law. The frequency domain and frequency domain polarization current density can be obtained by the decomposition of the Cole-Cole model. The current density of the frequency domain can be converted into a time domain current density by the positive cosine transformation. By analyzing the characteristics of the induced current density, polarization current density and the time domain of the total current density, the characteristics of the electromagnetic diffusion in the polarized medium are studied. The charge discharge process of the induced current and polarization current is studied and analyzed, and the polarization medium appears reasonably. By studying the characteristics of the electromagnetic diffusion in the polarization model of different charge rate and conductivity, the influence of different excitation parameters on the electromagnetic diffusion is obtained, and the understanding of the effect of the aero transient electromagnetic excitation is further deepened. The theoretical basis for the forward simulation of the subsequent chapters is provided. In this paper, taking the horizontal circular loop source as an example, this paper gives the expression of the vertical magnetic field at the center of the horizontal circular loop, using the positive cosine transform to calculate the step response and impulse response of the aeronautical transient electromagnetic excitation effect, and calculate the transient electromagnetic excitation response of the arbitrary wave form by the convolution technique. The effect of the same excitation parameters on the response of the aeronautical transient electromagnetic excitation. Through the forward modeling of the layered polarization model, the phenomenon of multiple sign reversal appeared in the aero transient electromagnetic response is explained reasonably. Finally, the inversion of the parameters of the aeronautical transient electromagnetic excitation is studied. The classical Occam inversion method is adopted to introduce the Occa first. The basic theory of M inversion method is that the parameters of Cole-Cole model are restricted reasonably in the inversion process, the stability of the inversion is improved and the multiple solvability of the inversion is reduced to a certain extent. The advantages and limitations of the inverse algorithm in this paper are given by the inversion of several typical theoretical layered polarization models. The results can lay a good foundation for the forward and forward research of the three dimensional transient electromagnetic excitation effect and provide some theoretical significance for further understanding of the excitation effect in the aero transient electromagnetic method.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P631.326

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