Comparing Integral Equation and Finite-Element Airborne Electromagnetic Modelling Using Public Domain Software

LeroiAir and ArjunAir are two computer programs used to model airborne electromagnetic data, however based on different mathematical algorithms. LeroiAir is a 3D thin plate program developed by the Commonwealth Scientific and Industrial Research Organisation (CSIRO). ArjunAir, also developed by CSIRO, is a 2.5D finite-element program. When these programs are applied to the modelling of discrete conductors, a key difference is in how they represent plates. In LeroiAir, the plates are infinitesimally thin. On the other hand, plates in ArjunAir require a minimal thickness. In this short paper, the two programs are used to model responses of simple subsurface models and these responses are compared. Both programs performed identically in models without plates, as expected. Though the results of models where plates were present were similar, a few differences could be identified. These differences, however, could be explained by physical effects (such as plate thickness or horizontal eddy currents induced on the flat top of the plates) or by modelling and discretization effects (such as number of cells, horizontal/vertical adaptation, and cell size compared to skin depth). They were not necessarily caused by the different algorithms used by the programs.