A comparison of shipborne and airborne electromagnetic methods for Antarctic sea ice thickness measurements

Abstract

The three-dimensional modelling program MARCO_AIR has been used to calculate the response of idealised pressure ridges to practical airborne and ship-borne electromagnetic systems. The model results clearly show the superior resolution of the horizontal coplanar ship-borne system compared to airborne measurements. However, sea ice keel thicknesses estimated via inversion of ship-borne single-frequency electromagnetic data are strongly dependent on relatively small variations in survey altitude. Inversion of helicopter electromagnetic data over 3D pressure ridge models shows that the maximum keel thickness is consistently underestimated, although airborne EM methods yield reliable thickness estimates over level ice. The vertical coaxial coil survey geometry offers excellent lateral resolution of multiple targets, but the anomalies of typical Antarctic sea ice pressure ridges would be too small to detect in practical surveys using a close-coupled (2?3 m) geometry. For a system with a coil separation of 8 m, the vertical coaxial responses are larger, and lateral resolution of the measurements at a flight height of 20 m is superior to a close-coupled system flown at an altitude of 10 m.