Doppler effects on high latitude HF paths during an ionospheric disturbance

The high latitude ionosphere is subject to great variability which makes propagation predictions much more difficult than at lower latitudes; increased absorption and rapid deterioration of the ionospheric layers can occur with little forewarning; see Cannon (1989). Ionospheric HF communications at high latitudes are often hampered by signal dispersion and Doppler spread and shift, which are caused by irregular and dynamically fluctuating ionisation of the propagation medium. To optimise the performance of an HF communication link in this environment it is likely that the system will need a variety of waveforms to match the prevailing propagation conditions. Under benign conditions a high data rate waveform can be used, but with degrading channel characteristics this must be replaced by slower and more robust schemes to keep the bit error rate at an acceptable level. This selection of waveform must be made with information from channel probes and a thorough understanding of ionospheric propagation. This paper presents results of measurements over two Scandinavian paths, from Harstad in northern Norway to Kiruna in northern Sweden (194 km) and from Harstad to Tuentangen near Oslo, Norway, (1019 km). Data for 16 through 22 October 1995 are considered. During this period a disturbance occurred whereby the geomagnetic Q index in Kiruna reached values ⩾7 for several hours