Analyzing potential over-the-horizon radar site locations

Over-the-horizon radar (OTHR) systems, or skywave propagation systems, use the high frequency (HF) band (3 to 30 MHz) to “bounce” or “refract” a signal off the ionosphere to detect tracks of interest (TOIs) between 500 and 2000 nautical miles from the transmitter/receiver pair. This range is “an order of magnitude greater than is possible with conventional line-of-sight radars” [1]. Since their initial employment, OTHR systems have significantly improved in abilities to detect and track TOIs such as aircraft, ballistic and cruise missiles, and ships [2]. The refraction utilized by OTHR systems occurs on the D-, E-, and F-layers of the ionosphere. Unfortunately, ionospheric refractivity (and hence OTHR fidelity) greatly depends upon environmental conditions including (but not limited to): time of day, sunspot activity, ground clutter, and season of the year. OTHR systems must dynamically shift transmission frequencies to account for these environmental conditions, resulting in wide variations in performance, particularly against small/slow targets. Unfortunately, during “night, the D-layer disappears, [and] the E and F regions experience a substantial decrease in ionization,” thereby decreasing the ability of the ionosphere to refract HF signals [2]. The effect of ionosphere environmental conditions on OTHR performance presents unique challenges in identifying preferred radar siting location strategies. Despite these limitations, OTHR systems present potential opportunities to dramatically improve surveillance capabilities. This research effort presents analytical techniques developed to analyze potential site locations in order to determine which provide the best track establishment and continuity metrics (using an accredited OTHR representation model) relative to other potential site locations. A complete technical description of an OTHR system is available in [1].