Measurements of Doppler and multipath spreads of HF signals received over several northerly paths

The northerly ionosphere is a dynamic propagation medium that causes HF signals reflected from this region to exhibit delay, Doppler shifts and Doppler spreads that significantly exceed those observed over mid-latitude paths. These Doppler effects are due to large-scale motion of the ionosphere and/or the turbulent motion of plasma irregularities that are a common feature of the auroral and polar cap ionospheres. From the perspective of communications systems, such large delay and Doppler spreads can result in a significant degradation in system performance (e.g. in achievable data throughput).