The acquisition of airborne electromagnetic (AEM) data colocated with water well data provides an essential data set for constructing an accurate rock-physics relationship between resistivity from AEM and lithology from wells. Results from an AEM survey in Butte and Glenn Counties, California, USA, where 41 water wells are located within 100 m of the AEM flight lines, provide a unique opportunity to investigate the effect of water wells on AEM data. Based on systematic numerical analyses and examination of the field data, we find that the only noise source related to the wells that affects the AEM signals in our study area is the power lines; the effect of the steel casings in the study area is negligible. Our numerical simulations yield two important findings: (1) the effect of the power line is mainly dependent upon the resistivity of the ground pathway between the base of the power-line poles, and (2) for the resistivity structure in the study area, when the ground contact resistance is sufficiently low, the effect of the power line will be observed in the AEM data until there is a separation distance of 174 m from the power line; the total power-line percentage effect less than 3% has been considered to be negligible. However, we find that, in the field data, an average separation distance between the power line and high-quality AEM data (i.e., no impact from the power lines) is only 60% of this predicted distance. We attribute this to the high ground contact resistance caused by degradation of the grounded electrodes located at the bottom of the power-line poles. For our 41 wells, after removing any soundings contaminated by power-line noise, we are left with high-quality soundings located 0–160 m from the water wells, with an average distance of 77 m.

中文翻译：

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电力线对时域机载电磁数据的影响

与水井数据共存的机载电磁（AEM）数据的采集为构建AEM的电阻率与井的岩性之间的精确岩石物理关系提供了重要的数据集。美国加利福尼亚州比尤特县和格伦县的AEM调查结果表明，AEM飞行路线100 m内有41口水井，这为调查水井对AEM数据的影响提供了独特的机会。通过系统的数值分析和现场数据检查，我们发现，影响研究区域AEM信号的与油井有关的唯一噪声源是电力线；而油井的噪声源仅次于电力线。钢制外壳在研究区域内的影响可以忽略不计。我们的数值模拟得出两个重要发现：（1）电源线的影响主要取决于电源线两极之间的接地路径的电阻率，（2）当接地电阻足够低时，研究区域的电阻率结构，将在AEM数据中观察电源线的影响，直到与电源线的距离为174 m；总的电力线百分比效应小于3％被认为可以忽略不计。但是，我们发现，在现场数据中，电源线与高质量AEM数据之间的平均间隔距离（即，电源线没有影响）仅为此预测距离的60％。我们将其归因于由于位于电源线电极底部的接地电极的退化而导致的高接地电阻。对于我们的41口井，