LAUSR

High-frequency over-the-horizon radars (OTHR) provide an economical means to detect and track noncooperative air targets over large expanses of land and sea. Due to the dynamic nature of the ionosphere, an OTHR requires a frequency management system where the operating frequencies and launch angles (azimuth and elevation) change periodically to maintain constant target detection. Accurate electron density models are required for the purpose of improving OTHR performance and for system planning and design. This is particularly true in the polar regions where large-scale electron density structures taking the form of patches and arcs of enhanced electron density are the common features of the F-region ionosphere. These structures form tilted reflection surfaces for HF radiowaves and result in propagation well displaced from the great circle direction. The effects of patches on the ray paths have been simulated, and their impact on OTHR frequency management is illustrated.