Correction schemes for self-demagnetisation

Abstract

Aeromagnetic surveys collected over bodies of high susceptibility record fields that have been significantly affected by self-demagnetisation. These effects complicate interpretation as the amplitude of the magnetic response scales non-linearly with the susceptibility. Analytic modelling is only carried out for compact ellipsoidal bodies and most approaches break down in the high susceptibility limit. It therefore of interest to develop tools for understanding and modelling of self-demagnetisation effects to support geophysical exploration. We present a modelling scheme based on multiple prismatic sub-volume bodies in a 3D grid for investigating and testing self-demagnetisation effects. This scheme, and another recent iterative scheme based on multiple spherical voxels, is tested to demonstrate self-demagnetisation effects on simple bodies. The schemes are verified against the known analytic results for a spherical body and the results for a cubic body. The prismatic scheme is then used to model a dipping magnetite sheet for comparison against real data where self-demagnetisation effects are thought to be important. Finally, we demonstrate the main advantage of the correction scheme by modelling multiple magnetic bodies in a 3D grid. These correction schemes are aimed at improving current magnetic modelling techniques and providing solutions for dealing with complex and highly susceptible bodies.