GETMAG ? a new magnetic tensor gradiometer for exploration

Abstract

CSIRO and Australian exploration companies have developed a new instrument for mineral exploration. The GETMAG (Glass Earth Tensor Magnetic Airborne Gradiometer) instrument measures the magnetic gradient tensor and the components of the magnetic field. The sensors are high temperature superconducting (HTS) quantum interference devices (SQUIDs) operating at liquid nitrogen temperature. A superconducting transformer coupled to a SQUID magnetometer is rotated to detect all gradients perpendicular to the rotation axis. Three SQUID-loop assemblies are required to measure the full tensor. Field trials demonstrate that the inversion of a few tensor measurements yields as much information as a high-resolution total magnetic intensity (TMI) survey. Direction to individual sources and their magnetic moments (reduced according to distance) can be determined directly from the tensor. GETMAG has applications in mineral exploration, environmental studies, ordnance detection, ship degaussing, submarine tracking and monitoring of marine currents. The project was funded by CSIRO, BHP, De Beers, MIM, Newmont and WMC.