A Unique Observation of the Polarization State of a Single Mode Radio Wave Traversing Through the Ionosphere

The polarization state of transionospheric radio waves can be determined using the cross-dipole antennas of the Radio Receiver Instrument (RRI) on the e-POP/CASSIOPE/Swarm-E satellite. Experiments have been conducted between the RRI and ground radars. In the plasma environment of the terrestrial ionosphere, high frequency (HF) radio waves propagate via both magnetoionic modes, the O- and X-modes, combined. The experiments have shown the high frequency (HF) radio waves to propagate via both magnetoionic modes, the O- and X-modes, combined. For a special RRI observation and an HF transmitter located in Ottawa, Canada on the 12 May 2017, only one magnetoionic propagation mode reached the satellite. The observed polarization state had a stable orientation angle, thus indicating no Faraday rotation, but the ellipticity angle uniformly varied from -19° (left elliptical) to linear (0°) and finally 30° (right elliptical) within a latitude span of 15°. Supported by magnetoionic ray trace modeling and ground-based ionogram observations for the ionospheric state, only O-mode radio waves reached the satellite for the entire pass, whereas X-mode waves were refracted towards the ground. This experiment presented a special opportunity to examine an O-mode only polarization state for transionospheric propagating radio waves.