The diffraction of VLF radio waves by the Antarctic ice cap

Measurements of the amplitude and phase of VLF radio signals from the Omega transmitters on La Reunion Island and in Argentina have been made on routine Antarctic re-supply nights from Christchurch, New Zealand. It has been found that when the propagation paths to the transmitters cross the Antarctic ice cap, the direct path signals are very rapidly attenuated below the receiver noise level, the dominant signal source then being provided by the radio waves diffracting around the edge of the ice cap. These results have been made possible by the simultaneous use of the phase and amplitude data in a synthetic aperture antenna type analysis.