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The radar horizon with an antenna height of 75 feet (23 m) over the ocean is 10-mile (16 km). However, since the pressure and water vapor content of the atmosphere varies with height, the path used by the radar beam is refracted by the change in density. With a standard atmosphere, electromagnetic waves are generally bent or refracted downward.
Within the RAF, a new term began to be used, a "horizon limited radar", a system that could see anything above the radar horizon. Due to the curvature of the Earth, and assuming the maximum possible altitude of an air-breathing aircraft was about 60,000 feet (18,000 m), this corresponds to a range of 320 nautical miles (590 km; 370 mi).
The frequency of radio waves used by most radars, in the form of microwaves, propagate in straight lines.This generally limits the detection range of radar systems to objects on their horizon (generally referred to as "line of sight" since the aircraft must be at least theoretically visible to a person at the location and elevation of the radar transmitter) due to the curvature of the Earth.
Eglin AFB Site C-6 is a United States Space Force radar station which houses the AN/FPS-85 phased array radar, associated computer processing system(s), and radar control equipment designed and constructed for the U.S. Air Force by the Bendix Communications Division, Bendix Corporation.
An over-the-horizon radar sited in the USSR would help solve this problem, and work on such a system for this associated role started in the late 1960s. The first experimental system, Duga, was built outside Mykolaiv in Ukraine , successfully detecting rocket launches from Baikonur Cosmodrome at 2,500 kilometres (1,600 mi).
The Jindalee Operational Radar Network (JORN) is an over-the-horizon radar (OHR) network operated by the Royal Australian Air Force (RAAF) that can monitor air and sea movements across 37,000 square kilometres (14,000 sq mi). [citation needed] It has a normal operating range of 1,000–3,000 kilometres (620–1,860 mi). [1]
Mill Valley Air Force Station' received an AN/FPS-8 in 1955 (subsequently converted to an AN/GPS-3), and during 1956 an AN/FPS-4 height-finder radar operated (superseded by an AN/FPS-6 in 1958.) Mill Valley began operating an AN/FPS-7 search radar 1 in 1960 at facility built in 1959 by the General Electric company. [12]
Thule Site J (J-Site) is a United States Space Force (USSF) radar station in Greenland near Pituffik Space Base for missile warning and spacecraft tracking.The northernmost station of the Solid State Phased Array Radar System, the military installation was built as the 1st site of the RCA 474L Ballistic Missile Early Warning System and had 5 of 12 BMEWS radars.