Determining Ionospheric Parameters over Regions of Denied Access

Utilization of high frequencies for over-the-horizon surveillance necessitated a refined approach to the determination of actual ray paths. Various ray-tracing programs have been developed. The basic problem lies in accurately determining values of the appropriate ionospheric parameters. A possible means is by utilization of oblique sounding devices located at the path terminals to provide 1) relative propagation time difference (Δt) between the modes, 2) maximum frequency propagated by any given mode (MUF), and 3) difference in MUF between the various modes (ΔMUF). The technique has not been fully verified; preliminary results are encouraging.