Simulation of the effect of convecting patches of enhanced electron density on HF Over-The-Horizon Radars (OTHRs) in the polar regions

High frequency Over-the-Horizon Radars (OTHR)provide an economical means to detect and track non-cooperativeair targets over large expanses of land and sea. Owing to thedynamic nature of the ionosphere, an OTHR requires a frequencymanagement system where the operating frequencies and launchangles (azimuth and elevation) change periodically to maintainconstant target detection. Accurate electron density models arerequired for the purpose of improving OTHR performance andfor system planning and design. This is particularly true in thepolar regions where large-scale electron density structures takingthe form of patches and arcs of enhanced electron density area common feature of the F-region ionosphere. These structuresform tilted reflection surfaces for HF radiowaves and result inpropagation well displaced from the great circle direction. Theeffects of patches on the ray paths have been simulated, and theirimpact on OTHR frequency management is illustrated.