多通道瞬变电磁法频率域比值算法及视电阻率计算研究

视电阻率在电磁法勘探中起重要作用，可以作为初步解释结果，多通道瞬变电磁法通过大地脉冲响应的峰值时刻定义视电阻率.鉴于传统方法计算峰值时刻视电阻率需要恢复完整大地脉冲响应，本文通过研究大地脉冲响应及其频谱特征，提出一种新的频率域比值法.利用参考谱及其与一般谱的伸缩因子计算一般谱的峰值时刻，进而得到视电阻率.该方法只需大地脉冲响应单个频点幅度谱，从而不用估计整个大地脉冲响应.实际计算时，可以用大地脉冲响应多个频点幅度谱得到平均视电阻率.模拟数据与实测数据结果表明，在一维介质中，频率域比值法可以得到合理的视电阻率.

Study on MTEM frequency-domain ratio method and apparent resistivity calculation

Apparent resistivity has played a significant role in electromagnetic exploration and is able to be used for preliminary interpretation. Multi-channels transient electromagnetic method defines the apparent resistivity using the peak time of earth impulse response. However, traditional method evaluating peak-time apparent resistivity need to recover the entitle earth impulse response. In this paper, a new frequency-domain ratio method is proposed by studying characteristics of both the impulse response and its spectrum. Apparent resistivity is obtained by calculating the peak time of the general spectrum using reference spectrum and scaling factor between the reference spectrum and the general one. Only single-point spectrum is needed to get the peak time, instead of estimating the entitle earth impulse response. In practical, multiple-points spectrum can be exploited to obtain the averaged apparent resistivity. The results from synthetic and field data show that frequency-domain ratio method gives reasonable apparent resistivity in one dimensional media.