瞬变电磁法阻尼系数对有效采样时刻影响研究

瞬变电磁法的探测深度主要由观测时间决定,早期观测信号包含浅层地电信息。接收线圈过渡过程对早期瞬变电磁信号影响严重,导致信号的有效采样时间起始点后延,丢失浅层探测信息。野外工作中,接收线圈两端通常外接阻尼电阻来调整线圈的工作状态。本文基于接收线圈等效电路模型,分析接收线圈阻尼系数对过渡过程的影响,比较了不同工作状态下的瞬变电磁响应特性,计算了不同阻尼系数时的视电阻率误差,并分析了有效采样时刻随阻尼系数的变化趋势。结果表明,浅层探测中过渡过程给早期视电阻率计算带来很大误差,数据处理时须舍弃早期信号或予以校正。在临界阻尼的情况下,过渡过程影响总体最小,为接收线圈最佳工作状态。

Influence of Damping Coefficient on the Effective Sampling Time of Transient Electromagnetic Method

Detecting depth of transient electromagnetic method is mainly determined by observation time.The early time observation signal contains information on shallow ground.The transition process of receiver coil which is highly related to distortion of early time transient electromagnetic signals can lead to the time delay of starting point of the effective sampling signal and the loss of the shallow exploration information.During field experiment,the work state of receiver coil is usually adjusted by an external damping resistor.The equivalent circuit model of the receiver coil is established to analyze the influence of damping coefficient on the transition process and to investigate the transient electromagnetic response characteristics under different states.Based on the analysis above,the apparent resistivity error under different damping coefficients is calculated and the relationship between the effective sampling time and the damping coefficient is also given.The result shows that the transition process could cause huge calculation errors on early time apparent resistivity during shallow detection.Thus the early time transient electromagnetic signs should be removed or corresponding calibration should be made during data processing.Under the state of critical damping,optimal state of receiver coil is achieved with overall minimal impact of transition process.