Gem-2A Broadband Airborne Em System

A helicopter towed bistatic EM system capableofsimultaneously transmitting and receiving at<br>several user-selected frequencies has been developed, and is currently operational in mineral<br>exploration programs in Australia. This system employs advanced digitally controlled<br>transmitter electronics providing flexible user selections for current waveforms, as well as<br>advanced built-in digital signal acquisition and processing including real-time sine/cosine<br>correlation for spectral analysis of the data. A reference, or “bucking” coil is incorporated,<br>which is wired in reverse polarity to the primary receiver coil, thus removing the direct system<br>response as observed iq the absence of a conductive target (i.e. at high altitudes). This feature<br>is critical in maximizing the observability ofthe weaker response from currents induced in the<br>earth. A case study is presented with presentations of apparent conductivity maps for real<br>survey data.