Comparison of measured and calculated oblique-incidence radio-wave propagation characteristics

During the period from January to December 1966, measurements have been made of the mode structure and absorption loss for high-frequency (h.f.) transmissions received over oblique propagation paths ranging in length from 500 to 1000km. The propagation characteristics for these circuits have been evaluated for the conditions appropriate to the period of observation by means of a ray-tracing analysis developed from the Booker quartic equation and also by two `prediction¿ methods. In general, the predicted values of absorption agree well with the experimental results, although some discrepancies occur during the winter months since neither of the prediction methods makes allowance for the anomalous winter behaviour. The accuracies of the ray-tracing results are dependent on the validity of the assumed ionospheric model, and, when electron-density/height distributions derived from vertical-incidence soundings at the receiving site are employed, the ray-tracing calculations of mode structure and absorption loss are found to be consistent with experimental observations of these parameters.