【作者】 万玲；

【导师】 林君；

【作者基本信息】 吉林大学 ， 测试计量技术及仪器， 2010， 硕士

【摘要】 瞬变电磁方法也称时间域电磁法,是一种基于电性差异,寻找低阻目标体,研究浅层至中深层地电结构的一种探测方法,目前广泛应用于寻找矿产资源和水文勘探中。瞬变电磁法比较常用的工作装置有中心回线、重叠回线、定回线源和偶极装置。其中,定回线源装置在实际测量时只需敷设一次发射线圈即可完成整个测区的探测,解决了野外工作中敷设线圈麻烦的难题,提高了工作效率,从而备受关注。本文主要针对定回线源瞬变电磁数据反演算法进行研究,取得了以下几方面研究成果:首先计算了定回线源的瞬变电磁响应,采用圆回线与方形回线等效的办法,提高了正演速度;其次,计算了定回线源晚期视电阻率拟合方程。将响应电压拟合转换为视电阻率拟合,避免了因响应电压动态范围大而造成的反演计算中雅克比矩阵不稳定等问题,同时,可以通过观察视电阻率随深度的变化特征,估计出地下地质体的相关物理参数作为反演中的初始模型参数;再次,研究了广义逆矩阵理论和奇异值分解方法,通过对比最小二乘法和奇异值分解法在处理瞬变电磁数据时的优缺点,提出了采用加阻尼截断奇异值分解方法对瞬变电磁数据进行反演解释;最后,采用上述方法对内蒙古二连浩特地区野外瞬变电磁数据反演计算,反演结果与视电阻率解释结果一致,验证了本文提出的数据处理方法的正确性和实用性。更多还原

【Abstract】 Transient electromagnetic method can also be called Time-domain electromagnetic method(TEM),is a kind of geophysical exploration method based on electrical difference of properties for surveying low resistance targets and researching the earth structure of shallow and middle shallow. The most popular devices of TEM are center-loop,overlap-loop and dipole-dipole device,and the data processing softwares of these devices have been used widely.However,when we work outside using these devices,the amount of work is great for we need to move the transmitter loop again when survey another point.So more and more attention is paid to the fixed-loop devices.This paper is based on the SVD,studying the TEM data processing algorithm of fixed-loop. The main research work and achievements are as follows:1.Know deeply the work principle,equipment and instrument structure of the MRS and TEM associated instrument. Study deeply the basic theory of electromagnetic fields,as for the work equipment of the TEM mode, transient electromagnetic field’s expression is derived for fixed Loop Source on Multilayered.2. Then, the arithmetic is proved to be feasible and correct by making contrastive research between the center point of the center loop’s transient electromagnetic response and the center point of the fixed Loop’s transient electromagnetic response using several groups of the earth model.At the same time,making the circular loop response equivalent to the square loop response,the forward computing time is decreased greatly. This can provide theoretical basis for the field data’s inversion.3.Caculate the late time apparent resistivity of the large fixed loop.Using the apparent resistivity to interpret is more visually than using the response voltage,and the apparent resistivity can also be the initial model for the field data’s inversion.4.Study the generalized inverse theory and singular value decomposition(SVD),compare the SVD method and the damping least square method,and use a new method called damping truncated singular value decomposition(DTSVD) method that can get the mutual complementary of the two methods,reduce the need of the precisiion for initial model parameter estimation,increase the convergence rate,make the inversion time shorter. 5. Simple and easy to operate to TEM inversion for the fixed loop source on layered earth graphical user interface is designed with the graphical user interface tool of MATLAB.6.By fitting the TEM data of the theoretical model with the damping truncated singular value decomposition, we find that the fitting rate is fast,the fitting result is correct, the inversion arithmetic is proved to be feasible.7.We studied the DTSVD method inversion for the wild transient electromagnetic data in Erlianhaote in the Inner Mongolia.By making the contrast between the sectional drawing of apparent resistivity , we found that the result was agreetable.the inversion arithmetic is proved to be feasible in the pratical application.更多还原