We can learn even more about the positions and movements of whistler ducts in the magnetosphere from a triangulation experiment using two goniometers sited at opposite ends of a suitable base line. It was for this reason that the VLF recordings at Ryvingen were made in close collaboration with the British Antarctic Survey Base at Halley where another goniometer supplied by Sheffield is operated. When the same whistlers are received at both stations, it is possible to locate the position of the end of the duct which has brought the whistlers from the northern hemisphere.
Halley and Ryvingen were not the only VLF receivers recording data during the winter of 1980, for others were being run simultaneously at SANAE and the American stations at Palmer and Siple (Stanford University). Sheffield University ran temporary VLF receivers in the Newfoundland area of eastern Canada, which is the region magnetically conjugate to the base at Halley. This allowed the movements of both ends of whistler ducts to be monitored.
Ryvingen data are interesting not only because they will provide a picture of the detailed structure in the magnetosphere near the magnetic field line passing through the base but because they also form part of a much larger data set collected by a chain of international stations in the Antarctic and around the world.