ATTEM系统中电流关断期间瞬变电磁场响应求解的研究

在瞬变电磁法中，由于发射电流关断时间不为零、接收线圈的谐振频率有限，早期瞬变电磁信号发生畸变，只能舍弃，因此存在着探测盲区. 针对这一问题，研究了瞬变电磁方法中发射电流关断期间总磁场的形成过程，论证了一次场、二次场和总瞬变场的关系，分析了接收线圈的频率特性和关断时间对瞬变电磁场的影响，提出从总磁场中剔除一次磁场影响的方法，从而获得电流关断期间和电流关断后的早期瞬变电磁场. 采用吉林大学自主研制的瞬变电磁测量系统(ATTEM)在长春市伊通河活断层进行勘探，进一步验证了算法的有效性，缩短了瞬变电磁法的勘探盲区，实现了近地表4 m以下的勘探，可以清晰地分辨近地表的低阻异常，提高了浅层探测精度和分辨率.

A study on solution of transient electromagnetic response during transmitting current turn_off in the ATTEM system

When the transient electromagnetic method is used for survey,a blind zone will exist because of the existence of transmitting current's switch-off time,the limitation of the receiver winding's resonance frequency,and the distortion of the early period's transient electromagnetic signal.This paper first analyzes the formation process of the total magnetic field during the switch-off time of transmitting current.We discuss the relation among the primary field,the secondary field and the total transient electromagnetic field and demonstrate the influence of the frequency feature and switch-off time of the receiver winding on the transient electromagnetic field.We then propose a method to remove the effect of the primary field from the total transient electromagnetic field.Using this method,we can obtain the transient electromagnetic fields of the early period during and after the current switch-off period.Using the ATTEM system developed by Jilin University,we conduct a fault investigation in the Yitong River area of Changchun.The field experiment results show a smaller blind zone of the transient electromagnetic method,a higher accuracy and resolution of shallow detection.It realizes survey implementation 4 meters below the earth's surface and clear differentiation of low resistance anomalies.The overall results prove the effectiveness of the proposed algorithm.