Airborne electromagnetic (EM) systems have evolved into two basic platforms since their introduction in the 1950s. The helicopter-borne frequency-domain systems (HEM) use narrow-band, low-moment transmitters and closely spaced receivers with a rigid geometry between the transmitter and receiver coils. A wide range of conductance discrimination, excellent spatial resolution, and moderate depth penetration characterizes these systems. The fixed-wing time-domain systems (AEM) use wide-band, high-moment transmitters and separated receiver coils in a geometry that is not rigid. These systems have a moderate range of conductance discrimination, moderate spatial resolution, and much greater depth penetration than HEM systems. Since 1995 there have been...

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