A NEW MULTICOIL AERIAL ELECTROMAGNETIC PROSPECTING SYSTEM

Abstract

A helicopter‐towed multicoil electromagnetic system was developed using a 30‐ft bird and a transmitted frequency of 918 Hz. Its primary features of interest are (1) low aerodynamic and geological noise, (2) three‐dimensional vector recording of anomalies, and (3) quantity of geological information which is extracted by a computer‐oriented interpretive procedure. The multicoil system‐was developed to obtain more diagnostic geologic information about a conductor than was possible with other aerial electromagnetic equipment. This led to two approaches: (1) three‐dimensional recording of anomalies was developed to provide information on the electrical current distribution within the conductor and, hence, on the geometry of the conductor and (2) high‐resolution, low‐frequency design was chosen to bias the response of the system toward high‐conductivity targets to minimize interference from the usual geologic noise sources, thereby enhancing the response of discrete massive sulfide conductors. A consequence of these design criteria is a system yielding an advance in the state‐of‐the‐art of aerial electromagnetic exploration.