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radio systems. From the point of view Working Group 2 of the COST 296 Action, interest lies with effects associated
with propagation via the ionosphere of signals within the HF band. Several aspects are covered in this paper:
a) The directions of arrival and times of flight of signals received over a path oriented along the trough have
been examined and several types of propagation effects identified. Of particular note, combining the HF observations
with satellite measurements has identified the presence of irregularities within the floor of the trough that
result in propagation displaced from the great circle direction. An understanding of the propagation effects that
result in deviations of the signal path from the great circle direction are of particular relevance to the operation
of HF radiolocation systems.
b) Inclusion of the results from the above mentioned measurements into a propagation model of the northerly
ionosphere (i.e. those regions of the ionosphere located poleward of, and including, the mid-latitude trough)
and the use of this model to predict the coverage expected from transmitters where the signals impinge on the
c) Development of inversion techniques enabling backscatter ionograms obtained by an HF radar to be used
to estimate the ionospheric electron density profile. This development facilitates the operation of over the horizon
HF radars by enhancing the frequency management aspects of the systems.
d) Various propagation prediction techniques have been tested against measurements made over the trough
path mentioned above, and also over a long-range path between Cyprus and the UK.
e) The effect of changes in the levels of ionospheric disturbances on the operational availability at various
data throughput rates has been examined for the trough path mentioned earlier.
The topics covered in this paper are necessarily brief, and the reader is referred to full papers referenced
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