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定源回线装置的瞬变电磁法因其发射磁矩强,勘查深度大主要用于详查阶段来确定目标地质体的中心、埋深、边界以及倾角等几何参数.定源回线装置条件下一般测量三个分量的瞬变响应数据,而目前流行的解释方法仅为一维反演和视电阻率成像,并且大多只利用单个分量,还未充分利用三分量瞬变响应的有用信息.目前还缺少实用快速的实现三维三分量反演的有效方法.为充分利用实测三分量瞬变响应数据,并且获得更加可靠的目标地质体的信息,本文提出了基于等效电流环的三分量纯异常三维反演方法.理论表明受激发的导电体产生的涡旋电流早期分布在边缘或表面,之后向中心位置移动.即涡旋电流可以用不同时刻的等效电流环来等效,早期的电流环反映异常体的边界,而晚期的电流环主要反映异常体的中心.因此通过反演不同时刻等效电流环的几何参数,可以获得目标地质体的几何形态.本文给出了自由空间电流环产生的三个分量磁场的表达式,并利用计算得到的三分量磁场值同时拟合由实测数据提取的纯异常三分量数据,最终获得不同时刻的等效电流环的参数.理论模型和实测数据反演结果表明,等效电流环反演结果能够较好确定导电体的中心位置、半径、埋深、倾向、倾角等几何参数.本文提出的基于等效电流环的解释方法同时利用三个分量数据,计算快速、可靠、使反演结果更加合理,为定源回线装置瞬变电磁法提供了一种有效的解释方法.
Because of its strong magnetic moment of emission, the transient electromagnetic method of the source return line is mainly used for the detailed investigation to determine the geometric parameters such as the center, depth, boundary and dip of the target geological body. Under the general measurement of three components of the transient response data, and the current popular method of interpretation is only one-dimensional inversion and apparent resistivity imaging, and most often use only a single component, the three-component transient response has not yet make full use of the useful information. At present, there is still a lack of practical and rapid method to realize the inversion of three-dimensional three-component.In order to make full use of the measured three-component transient response data and obtain more reliable information of the target geologic body, a three-component pure Anomalous 3D inversion method.The theory shows that the eddy current generated by the excited conductor distributes at the edge or the surface at an early stage and then moves to the center position.The eddy current can be equivalent to the equivalent current loop at different times, The current loop reflects the boundary of the anomalous body, while the late current loop mainly reflects the center of the anomaly. Therefore, by inverting the geometrical parameters of the equivalent current loop at different moments, The geometry of the target geologic body can be obtained.This paper gives the expressions of the three component magnetic fields generated by the free space current loop and uses the calculated three component magnetic field values to simultaneously fit the pure anomalous three component data extracted from the measured data and finally The parameters of the equivalent current loop at different moments are obtained.The theoretical model and measured data inversion results show that the equivalent current loop inversion results can well determine the geometrical parameters such as the center position, radius, depth, inclination and inclination of the conductor. The proposed method based on equivalent current loop also makes use of three component data simultaneously, which makes the calculation fast and reliable, and makes the inversion result more reasonable. It provides an effective explanation method for the transient electromagnetic method of the fixed loop device.