Natural Field Airborne Electromagnetics—History of Development and Current Exploration Capabilities

Abstract

The mineral resources exploration industry continuously expands the efficiency requirements for geophysical technologies. Due to their relatively inexpensive nature, coupled with the ability to rapidly acquire data over large areas, airborne electromagnetic technologies have been used for decades in subsurface exploration. Limitations on the depth of investigation of airborne platforms with controlled primary field sources is the main obstacle for using these systems in many geoelectrical conditions and geographical terrains. In addition, systems based on the time-domain principle are limited in applications requiring differentiations in a high resistivity range of the mapping parameter and suffer from parasitic electromagnetic non inductive natural effects in specific near surface conditions. Methods exploiting natural electromagnetic fields in the audio frequency range significantly increase depth of investigation and sensitivity to a wide range of resistivity contrasts including in the range of thousands of ohm-ms. A brief history of the development of the natural field airborne technology is provided accompanied by a comparison of the systems technical specifications. Field examples from the latest development in the airborne electromagnetic natural fields’ domain, MobileMT, demonstrate its exploration capabilities in both conductive and resistive environments, sensitivity to any direction of geoelectrical boundary, and detectability of near-surface discrete targets along with deeper structures.