瞬变电磁合成孔径成像方法分辨率的研究

发布时间：2018-03-27 07:25

本文选题：瞬变电磁法　切入点：微分电导成像　出处：《长安大学》2015年硕士论文

【摘要】：高精度瞬变电磁法成为当下地球物理勘探中一个非常热点的研究对象。目前国内外关于瞬变电磁的解释技术大致分为两类:一类是层状介质反演;另一类是电导率-深度转换的近似解释方法。等效导电平面法是一种重要的瞬变电磁近似解释方法,其根据视纵向电导及其导数曲线的特征能够直观地划分地层,基于等效导电平面法的基本原理,本文给出了视纵向电导和对应视深度的定义,进而求取视纵向电导关于深度的二阶导数。其二阶导数曲线在均匀介质中为恒为零,但在地层电性发生变化的位置或界面会产生尖锐的峰值,将相邻各测点曲线的较连续的峰值连起来会形成类似于地震成像中的同相轴,我们称为其为瞬变电磁微分电导成像。相较传统方法它对地下电性分布尤其是层状介质的情况反应得更为直观、清晰。多孔径瞬变电磁物理模拟证明瞬变电磁多孔径具有相干性,相邻位置的同一地质体的反射回波具有相关性,因此瞬变电磁资料可以进行多孔径合成成像。基于以上理论,本文借助于合成孔径雷达的思想,将微分电导信号进行相关分析,得到各测点间的相关系数,将相关系数在阀值范围之内的测点数据进行相关叠加,以达到提高信噪比、突出弱异常进而提高分辨率的目的。同时这种处理方式也将传统的以单点解释为主的处理方式发展成为以测点为中心的逐点推移多次覆盖的处理方法。采用相关叠加合成孔径的方法将极大提高航空瞬变电磁的分辨能力。本文通过对不同的理论模型进行数值模拟,分析了不同地电模型合成孔径的效果、得出了简单模型(单个地质体)合成孔径成像技术中最佳合成孔径长度关于地质模型参数的经验公式。以此为依据讨论了瞬变电磁合成孔径成像的横向、纵向分辨率,为实际工作提供了一定的参考价值。
[Abstract]:The high-precision transient electromagnetic method has become a very hot research object in geophysical exploration. At present, there are two kinds of interpretation techniques about transient electromagnetic at home and abroad: one is the inversion of layered media; The other is the approximate interpretation method of conductivity depth conversion. The equivalent conductive plane method is an important transient electromagnetic approximate interpretation method, which can visually divide the strata according to the characteristics of the apparent longitudinal conductance and its derivative curves. Based on the basic principle of the equivalent conductive plane method, the definitions of apparent longitudinal conductance and corresponding apparent depth are given in this paper, and the second derivative of apparent longitudinal conductance on depth is obtained. The second derivative curve is constant zero in homogeneous medium. However, sharp peaks occur at the position or interface where the electrical properties of the strata change, and the contiguous peaks of the curves of adjacent measuring points will form a phase axis similar to that in seismic imaging. We call it transient electromagnetic differential conductance imaging. Compared with the traditional method, it can react more directly to the distribution of underground electricity, especially to the case of layered media. Clear. The multi-aperture transient electromagnetic physical simulation proves that the transient electromagnetic multi-aperture has coherence, and the reflection echo of the same geological body in the adjacent position has the correlation, so the transient electromagnetic data can be used for multi-aperture synthetic imaging. In this paper, with the help of synthetic Aperture Radar (SAR), the differential conductance signal is analyzed and the correlation coefficient is obtained. The correlation coefficient within the threshold range is superimposed to improve the signal-to-noise ratio (SNR). At the same time, the traditional single point interpretation method has been developed into a point-by-point multiple coverage processing method with point by point as the center. Correlation is adopted. The method of stacking synthetic aperture will greatly improve the resolution of aeronautical transient electromagnetic. In this paper, different theoretical models are numerically simulated. The effects of synthetic aperture of different geoelectric models are analyzed. The empirical formula of the optimum synthetic aperture length in the simple model (single geological body) synthetic aperture imaging technique is obtained. Based on this, the transverse and vertical resolution of transient electromagnetic synthetic aperture imaging is discussed. It provides some reference value for practical work.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P631.325

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