High Frequency Radio Wave Transionospheric Propagation Polarization Studies from the RRI-SuperDARN Experiment

Abstract

The enhanced Polar Outflow Probe (ePOP) launched in September 2013 is the fifth Canadian satellite designed for space science observations. One of the 8 instruments it carries is the Radio Receiver Instrument (RRI) which is a passive cross-dipole radio observation instrument. The RRI detects incoming HF (High Frequency) radio waves and measures the polarization information (such as orientation angle and ellipticity angle) of the wave. Radio waves were transmitted from the Saskatoon SuperDARN (Super Dual Auroral Radar Network) radar in conjunction with RRI flybys. There have been 88 conjunctions between RRI and SuperDARN over 4 years (2014-2018). The changing polarization state of the radar signal as it propagates through the ionosphere, transionospheric propagation, is the scientific focus of this thesis. Polarization techniques are used to study and characterize the modifications to the polarization state of the transionospheric radar signal. By characterizing polarization phenomena new details of structure in the ionosphere can be observed and further understanding of HF transionospheric radio wave propagation. Of the 88 RRI-Saskatoon SuperDARN radar conjunctions, 49 flybys recorded usable data including polarization information used to characterize phenomena observed as a radio wave propagates through the ionosphere can be achieved.

Magnetoionic theory of transionospheric radio wave propagation is used in this thesis to predict the phenomena observed in the RRI-Saskatoon SuperDARN radar conjunctions. Phenomena such as the Faraday rotation effect and the Voigt effect are extracted from the theory and demonstrated to occur in the Saskatoon flybys. Features in the orientation angle and ellipticity angle of the Saskatoon flybys are compared and contrasted to previously reported transionospheric observations. The Faraday rotation reversal signatures observed in the auroral region portion of the Saskatoon flybys were found to be more variable than the reversal signatures of sub-auroral events. Danskin et al. (2018) reported considerably more constant observations of the Faraday rotation reversal signatures in RRI flybys in conjunction with an HF transmitter located at Ottawa, Ontario.

The Voigt effect oscillations observed were found to agree with derived magnetoionic theory. They are dependent on the rate of Faraday rotation and are observed throughout an entire RRI flyby. An interpretation of Voigt effect oscillations observations had yet to be reported in transionospheric radio wave propagation experiments before this thesis. Three distinct and consistent spikes in the ellipticity angle were observed in daytime, slewing, high-altitude flybys and such behaviour was not predicted by modelling. It is postulated that the spikes in ellipticity angle demonstrate that RRI is moving between regions of focusing and defocusing of O- and X-mode rays, or ``HF fades'' during these RRI flybys (James et al., 2006).