It is clear that HF communications cannot provide ubiquitous real-time communications services to the armed forces at high latitudes. The reason is the dynamic and rapidly changing propagation medium. However, HF communications offers infrastructure independent, long-range communications, at times providing real-time services and throughput at tens of kbit/s, but most of the time non-real time services like messaging, chat and file-transfer at lower data rates. HF communications is thus a complimentary “tool” to other means of communications, and it can be particularly well suited for certain situations. Particularly in the Arctic, the number of communication systems are not that many, but HF communications is one of them. If HF communications is going to be a part of the Norwegian communications infrastructure in the
future, Norwegian Armed Forces should be particulary well trained to use it with new, modern technology and ways to exploit the high latitude ionosphere.
This report has referenced some of the existing knowledge of the high latitude ionosphere and its implications on HF communications, it has suggested how networks can be set up to increase the robustness of communications, and it has pointed out that real-time ionospheric
measurements may be used to increase the performance of the networks.
Despite the existence of automated radio technology for use in the HF-frequency band, designed to adapt the signals to the variable channel conditions, we do believe that the HF-operators would benefit from having good knowledge of the high latitude channel. The measurements and analysis of this study may give the following knowledge and advice to the HF-communicator:
HF has traditionially been point-to-point communications (or broadcast). With new modern technology, networks should be designed so that communications is possible via different paths, exploring the space diversity of the high latitude ionosphere. A southern node could, for instance, be included in a high latitude network. Paths going in the southern direction in Norway or Sweden are affected by ionospheric disturbances, but to a lesser degree than the high latitude paths. Between 10 % and 50 % better linking probability can be gained by utilizing such space diversity. The largest gain is achieved during ionospheric disturbances.
In summer time the conditions for HF communications are the best (excellent in our measurements), and there is no pronounced diurnal variability. The solar-driven ionosphere seems to dominate over the auroral ionosphere.
In winter time there is a strong diurnal variation with good conditions only in a few hours around and after noon. The conditions are difficult in the hours of dawn and dusk, particularly for the hours 03–06 UT. Communication attempts should be avoided for these hours if exposure on air is a concern. The conditions are improved at night time because of enhanced ionization due to particle precipitation (auroral E-layers).
Normally this ionization is able to reflect higher frequencies, which should therefore be included in the frequency plans.
Following a solar storm there are many ionospheric disturbances occurring at different time lags and with varying characteristics. The exact shape of the ionization and absorption is impossible to predict in advance, but real-time ionospheric measurements can be used for space situational awareness. Such measurements will tell the HF-operator whether HF communications is expected to be working well or the chance of achieving communications is small. They may also indirectly indicate that technical failure of the equipment may be the problem.
Our comparison of the HF-measurements with other ionospheric data has shown that using such data may give useful insight into the prevailing propagation conditions, and give guidance for
making favourable choices for the communication networks. Real-time ionograms in combination with riometer measurements of absorption were found particularly useful.
We suggest that further work to increase the robustness of HF communications at high latitudes should include:
Examination of the space weather data sources available on the Internet, including radio amateur tools, with respect to usefulness at high latitudes and for the HF-operator. The criteria for the examination should be the physical phenomena of relevance to HF communications treated in this report, in particular ionospheric absorption and reflection. If traditional prediction programmes using real-time space weather data as input exist, they should be examined.
Selection of relevant space weather data sources providing real-time data as input to a software application, and development of this software application to a tailor-made, easy-to-use application for the HF-operator. Some of the results from this report can be used in the development. This task possibly includes:
o Negotiations with ionospheric observatories to make data available online, in appropriate formats. This may include for instance calibration of the measured absorption with regards to the quiet day curve.
o Further preparations of the data for use in the software application.
o Establishment of new measurement sites if necessary.
Already existing space weather sites such as [26] could possibly be expanded to include specific data for HF communications situational awareness.