Observations of Doppler spreading on HF signals propagating over high latitude paths

The high latitude ionosphere forms a highly dynamic and disturbed medium which can severely degrade the performance of HF radio systems when the signals propagate through these regions. One important parameter is the Doppler frequency spreading imposed on the signal by the movement of electron density irregularities in the ionosphere at the reflection points. The magnitude of the Doppler spreading has been quantified in a series of experiments undertaken on a range of frequencies across the HF band over several high latitude paths. Two of these paths are considered in this paper, one of which (Clyde River-Alert, 1345 km) was contained entirely within the polar cap whilst the second (Clyde River-Prudhoe Bay, 2955 km) was sometimes entirely within the polar cap and at other times crossed the auroral oval. Results obtained over two one-month periods, one in summer (July/August 1988) and one in winter (January/February 1989), are presented