A versatile integral equation technique for magnetic modelling

A requirement currently exists in both mineral exploration and environmenta l or engineering geophysics for a technique to model the magnetic fields ca used by bodies with large to extreme susceptibilities in which both induced and remanent magnetizations are significant. It is well known that modelli ng such magnetic fields is not amenable to any known approximation. It is a significantly difficult task that requires the solution of a magnetostatic boundary value problem. Analytical solutions to the problem are extremely useful for providing insight but generally of limited application in practi cal interpretation due to the geometrical complexity of real situations. Av ailable numerical solutions include both volume and surface integral equati on formulations. However neither of these are particularly efficient for th e purpose. An alternative surface integral equation formulation is presente d here which represents the required magnetic field in terms of a double la yer over the surface of the body. The technique accommodates both remanent and induced magnetization and is generally applicable to any 3D body in a m agnetic environment for which the Green's function is available. The presen t technique has significant advantages over other integral equation solutio ns in the geophysical literature. It is particularly economic in terms of t he density of the surface discretization and consequently the computational effort. Moreover, it is extremely robust. It is found to yield accurate so lutions for the type of thin bodies that cause numerical instability with o ther surface integral equation approaches. (C) 1999 Elsevier Science B.V. A ll rights reserved.