Novel dual frequency fixed-wing airborne EM system of Geological Survey of Finland (GTK)

Abstract

The Geological Survey of Finland (GTK) has upgraded its airborne geophysical system by developing a new dual frequency airborne EM system for its DHC Twin Otter aircraft. The coils are mounted on the wingtips and the configuration for both coil pairs is vertical-coplanar. The lower frequency is 3.1 kHz, and it is ideal for mapping good conductors like base metal ore deposits in Precambrian bedrock. The upper frequency of the system (14.4 kHz) is suitable for engineering and environmental applications where the conductivities of the targets are not very high. The two frequencies together provide more information for detailed interpretation of subsurface resistivity structure. Technical specifications of the new system are presented and compared to those of the predecessor. Careful calibration of the system is of crucial importance in quantitative interpretations of measured data. The calibration of the system is verified by flying at different altitudes over the sea, which can be regarded as a homogeneous and conductive half-space. An interpretation example is also given where the use of dual frequency data significantly improves the inversion of model parameters compared to the single frequency inversion.