3D EM modelling of Antarctic sea ice pressure ridges

Abstract

The use of airborne electromagnetic (AEM) surveys to measure Antarctic sea ice thickness is being investigated as a regional mapping tool to aid global climate studies. Undeformed sea ice floes are modelled as 1D structures. However, sea ice pressure ridge sails (in air) and keels (undersea) form convenient 2D and 3D targets. In order to use AEM techniques to study the distribution of ice thickness, it is first necessary to test if realistic sea ice structures can be modelled electromagnetically. Pressure ridge structures from drillhole sampling can in some cases be constructed from simple block models. Finite element and integral equation 3D EM modeling programs can then be applied to these structures to test for agreement, and to predict the AEM response, including topography (sails). EM modelling of frequency domain systems shows that good agreement is obtained at certain frequencies and that a vertical coaxial (VCX) transmitter?receiver coil configuration laterally resolves the ice keel better than a horizontal coplanar (HCP) configuration. Cross-sectional dimensions of the sails and keels are relatively small and mesh design is critical in order to avoid discretisation errors. Software and hardware constraints may limit successful EM modeling of multiple keels that combine sub-metre structures and coarser structures. For a given mesh, discretisation errors may lead to noisy EM response profiles depending on the frequency, coil geometry, and component (in-phase or quadrature). Adaptive mesh structures may be required to minimise discretisation errors.