Helicopter trial of magnetic tensor gradiometer

Abstract

A SQUID (Superconducting Quantum Intereference Device) rotating tensor gradiometer has been test flown in a helicopter-towed bird over a magnetic dipolar source. The bird was instrumented with fluxgates, tiltmeters, a gyroscope and GPS receivers to assist in levelling and positioning. After correcting for pitch, roll and yaw, the gradient tensor measurements along flight lines compare well with those calculated for the flight lines relative to the magnetic source. The uses and advantages in mineral exploration of magnetic tensor gradiometry have been discussed at previous ASEG meetings (2001 and 2004) and include the benefits of vector surveys without the disadvantage of extreme sensitivity to orientation, desirable mathematical properties of true potential fields (important in areas with strong anomalies), allowing rigorous continuation, RTP, magnetization mapping and redundancy of tensor components giving inherent error correction and noise estimates. A novel inversion/deconvolution procedure has been developed for locating and characterising dipole sources. Inversion using Euler deconvolution has been developed for locating a wider set of sources generally encountered in mineral exploration, such as spheres, sheets and pipes. A wide range of new types of processed data are available, including invariants, directional filters and depth slicing.