瞬变电磁接收装置对浅层探测的畸变分析与数值剔除

Analysis and numerical removing of distortion in transient electromagnetic receiver device for shallow sounding

从理论上对瞬变电磁系统的接收装置频率特性进行分析,得出了瞬变信号在早期发生畸变的根本原因,揭示出接收装置在发射电流关断期间和电流关断后对一次场和二次场的影响关系,给出基于导电球体模型下接收装置的谐振频率与最小取样时间的关系图,进而讨论了接收装置对浅层目标体探测的影响.当瞬变电磁测量系统在电流关断开始时刻记录全程瞬变响应和发射电流波形时,如果接收装置的位置和谐振频率已知,就可以通过数值计算方法从根本上剔除接收装置对早期瞬变信号的影响,即使接收装置存在过渡过程,也同样可以实现近地表浅层的探测,从而缩短瞬变电磁法的浅层勘探盲区,提高近地表的探测分辨率和精度.

Frequency characteristic of transient electromagnetic receiver device is analyzed in theory, thus the reasons of distortion in early-time are given. The effect of receiver device on primary field and secondary field is proposed. The relationship between the minimum sampling time and resonance frequency of receiver device based on conductor sphere model is illustrated; the effect of receiver device on shallow subsurface sounding is discussed, during and after the turn-off of transmitting current. If the resonance frequency and position of receiver device is known when the alltime transient responses and transmitting current are recorded as soon as transmitting current begin to shut off, the effect of receiver device can be removed by using numerical method. Even though the transition process of receiver device, the shallow subsurface sounding can be realized, the blind zone can be reduced and the sounding resolution and precision can be enhanced.