Propagation directions of high-frequency waves in the ionosphere

The direction of propagation of electromagnetic waves in the ionosphere from ground-based transmitters can be measured in the ionosphere by crossed dipoles in a single cold-plasma mode. In the Enhanced Polar Output Probe (e-POP), 6-m dipoles on the Radio Receiver Instrument connect to a high input impedance and act therefore as voltage probes from which the electric field of incoming waves can be simply computed. When combined with cold-magnetoplasma electric-field theory, the relationship of voltages on the two orthogonal dipoles is used to deduce the direction of arrival of an incoming wave in three dimensions. The technique is illustrated by application to e-POP/Radio Receiver Instrument observations of 6.2-MHz waves transmitted by the European Incoherent Scatter HF facility in Troms⊘, Norway.