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Enhanced Airborne Detection of Perfect Conductors through Estimation of Primary Field Components
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 72nd EAGE Conference and Exhibition incorporating SPE EUROPEC 2010, Jun 2010, cp-161-00450
- ISBN: 978-90-73781-86-3
Abstract
The induced electromagnetic field in very conductive targets, such as high-grade sulphide deposits, does not appreciably decay within the measurement time of an airborne EM system. Measurement of in-phase or on-time response in the presence of a large primary field is required to detect these targets. In this study, we calculate the primary field generated by the transmitter at the receiver and subtract this from the measured response to obtain the in-phase secondary response. Employing a large transmitter-receiver separation reduces the accuracy to which geometry of the system must be known, and GPS data provides the required resolution. A transmitter loop and a receiver bird were outfitted with GPS units, and towed by separate helicopters, 400m apart. This provided position and orientation information to calculate the primary field at the receiver. The in-phase total-field response of this survey configuration was sensitive enough to detect a very conductive plate target. Using magnetometer data from the receiver, we have now been able to resolve component data useful for determining the geometry of the target. It is hypothesized this configuration could detect a 200 x 100 m perfect conductor at 200m depth in a resistive host.