Magnetic and electromagnetic (EM) methods are perhaps the most convenient and popular<br>geophysical survey methods for detecting buried manmade objects. This is due to their nonintrusiveness,<br>light field logistics, high survey speed, and the high quality of information. Thus, they<br>should considered as precursors to additional geophysical surveys. Often, the information resulting<br>from the two methods are sufficient for characterizing buried objects. During the oral presentation, we<br>will present case history examples showing magnetic and EM data collected at sites that have a range of<br>environmental conditions and project objectives. We find through these and numerous other<br>comparisons that broadband EM data are usually superior to magnetic data in terms of the amount and<br>the quality of information. The monopolar EM anomaly is invariably easier to interpret, and thus can<br>locate a buried target more accurately than the dipolar magnetic anomaly. In addition, the EM method<br>senses both electrically conductive and magnetically permeable targets. In contrast, the magnetic<br>method responds only to permeable, or ferrous, metals. In that sense, the magnetic method should be<br>considered a subset of the EM method, or as a special “passive” EM method at zero frequency.


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