NEW DEVELOPMENTS IN AIRBORNE ELECTRO-MAGNETICS

The first airborne electromagnetic (AEM) systems were developed in Canada in the early 1950s. By the late 1970s, AEM instrument development focused in two directions: multifrequency, multicoil helicopter systems and timedomain, towed-bird systems. Modern helicopter AEM systems typically operate with two coil configurations (vertical coaxial and horizontal coplanar) and 4-7 frequencies ranging from 700 Hz to 70 kHz. High-density data acquisition permits removal of sferic noise by post-flight processing. Products that can be compiled from modern helicopter AEM surveys include composite profiles, profile maps, and color conductivity maps. Examples will be shown from Monts Stoke, Quebec. Time-domain, towed-bird AEM systems have been redesigned in the mid 1980s. Both INPUT® and GEOTEM® are presently operated with digital receivers, which are self-calibrating and permit a removal of sferics in real time. As examples of GEOTEM survey results, conductivity maps and composite profiles from Lynn Lake, Manitoba, will be shown. AEM systems have been used in systematic surveying in Canada; Ontario and Quebec have close to 1 million line km, mostly acquired with time-domain, towed-bird systems.