不规则回线瞬变电磁法一维烟圈反演研究

One-dimensional smoke ring inversion of irregular loop source transient electromagnetic method

瞬变电磁法中最常用矩形或圆形回线,但有时由于地形限制,只能使用不规则回线发射和接收.如果仍用现有的常规回线理论进行处理解释,得到的结果会存在很大的偏差.本文首先进行了不规则回线瞬变电磁法一维正演理论研究,基于电偶极子源的频率域响应公式,通过沿回线积分和时频转换,推导出不规则回线源在水平层状介质中的时间域响应公式.采用欧拉算法、高斯积分和快速汉克尔变换,计算不规则回线内任意一点处的磁场响应.利用改进的二分搜索法计算全区视电阻率,并在此基础上利用烟圈法反演电阻率和深度.通过四个典型地电模型的正反演计算,表明烟圈法反演能够有效反映地电模型的大致形态,可以用于不规则回线瞬变电磁数据的快速反演解释.

The rectangular or circular loop is most commonly used by ground transient electromagnetic method.but sometime we have to send and receive electromagnetic waves with an irregular loop due to the terrain restriction.If we still use the existing conventional loop theory to process and interpret Transient Electromagnetic Method(TEM)data that is collected with irregular loop,you will get a wrong result.In this paper,the one-dimensional forward theory of irregular loop transient electromagnetic method is studied firstly,Based on the frequency domain response formula of electric dipole source,the time domain response formula of irregular loop source in horizontal layered media is derived by integrating along the loop line and transforming time frequency.Using Euler algorithm,Gaussian integral and fast Hankel transform,the magnetic field response at any point in the irregular loop is calculated.The improved binary search method is used to calculate the total area apparent resistivity.and the smoke ring method is used to invert the resistivity and depth.Through the forward and inversion simulation of four typical layered models,It is shown that the Smoking inversion result can reflect the rough shape of layered model effectively,and can be used for the fast inversion interpretation of irregular loop transient electromagnetic data.