Observations of Electromagnetic Waves at Very Low Frequency in the Near Topside Ionosphere

The e-POP/Swarm-E Radio Receiver Instrument (RRI) on CASSIOPE detects very-low-frequency (VLF) broadcasts from national naval sources over the whole world. The propagation in question is the whistler mode whose dispersion relation allows a number of unique phenomena to be examined. Because the whistler mode is the only ionospheric magnetoionic mode propagating at VLF, the crossed 6-m dipoles feeding the RRI permit the whistler-mode elliptical electric fields to be measured. This allows the direction of arrival (DOA) of propagation at the satellite to be determined. Examples of wave reception from NWC (Australia), NLK (USA), NAA (USA), and DHO38 (Germany) show features of whistler-mode propagation in the topside ionosphere.