A simple theoretical model of the diffraction of VLF electromagnetic waves by the Antarctic icecap

The Antarctic continent has been modelled as a spherical cap whose pole is coincident with that of the South Pole, which totally absorbs VLF radio waves attempting to propagate over it. The propagation of Omega navigation signals around this model icecap has then been computed using Kirchhoff diffraction theory. Spherical caps extending to 66.5 and 75.5°S have been found to accurately model the signals from Omega La Reunion and Argentina, respectively, received on flights between Christchurch, New Zealand and Scott Base in Antarctica, up to the boundary of the theoretical icecap. These model icecaps were found to be good fits to the boundary of the Antarctic continent, when measured at the 1–1.5 km contour of ice thickness, in the region where the VLF waves diffracted around the icecap. The good agreement obtained between the experimental field strength data and those computed theoretically, using only simple diffraction theory, suggests that coastal refraction plays at most only a secondary role in circumpolar propagation.