Time of flight measurements over a radio link from Uppsala to Bruntingthorpe and their application to testing predictions methods that approximate the ray tracing technique

Time of flight measurements (TOF) over the radio link between Uppsala (Tx: 59.9°N, 17.6°E) and Bruntingthorpe (Rx: 52.5°N, 1.1°W) have been performed every 2 min at six frequencies (4.637, 6.954, 8.008, 10.391, 11.118, and 14.364 MHz) during the period November 2006–January 2008. Such measurements have been compared with the TOF provided by three prediction methods that approximate the ray tracing technique: IRI-95, SIRM&BR_D, and ICEPAC. The root mean square deviation (rms) between TOF monthly median measurements and TOF monthly median predictions and the differences (DP) between the length of the median and predicted ray path have been calculated. The results, which are presented in terms of rms and DP for different seasons and different time periods, have indicated that the approximate methods are inadequate and that for more accurate predictions ray tracing techniques should be applied

Aspects of HF radio propagation

<p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">radio systems. From the point of view Working Group 2 of the COST 296 Action, interest lies with effects associated</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">with propagation via the ionosphere of signals within the HF band. Several aspects are covered in this paper:</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">a) The directions of arrival and times of flight of signals received over a path oriented along the trough have</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">been examined and several types of propagation effects identified. Of particular note, combining the HF observations</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">with satellite measurements has identified the presence of irregularities within the floor of the trough that</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">result in propagation displaced from the great circle direction. An understanding of the propagation effects that</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">result in deviations of the signal path from the great circle direction are of particular relevance to the operation</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">of HF radiolocation systems.</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">b) Inclusion of the results from the above mentioned measurements into a propagation model of the northerly</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">ionosphere (<em>i.e. </em>those regions of the ionosphere located poleward of, and including, the mid-latitude trough)</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">and the use of this model to predict the coverage expected from transmitters where the signals impinge on the</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">northerly ionosphere.</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">c) Development of inversion techniques enabling backscatter ionograms obtained by an HF radar to be used</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">to estimate the ionospheric electron density profile. This development facilitates the operation of over the horizon</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">HF radars by enhancing the frequency management aspects of the systems.</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">d) Various propagation prediction techniques have been tested against measurements made over the trough</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">path mentioned above, and also over a long-range path between Cyprus and the UK.</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">e) The effect of changes in the levels of ionospheric disturbances on the operational availability at various</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">data throughput rates has been examined for the trough path mentioned earlier.</p> <p style="margin: 0.0px 0.0px 0.0px 0.0px; font: 9.0px Times;">The topics covered in this paper are necessarily brief, and the reader is referred to full papers referenced</p> <br /&gt