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Encyclopedia > Over the horizon radar

Over-the-horizon radar, or OTH (sometimes also beyond the horizon, or BTH), is a design concept for radar systems to allow them to detect targets at very long ranges, typically up to thousands of kilometers. Several OTH radar systems were deployed starting in the 1960s as part of early warning radar systems, but these have generally been replaced by airborne early warning systems instead. OTH radars have recently been making something of a "comeback", as the need for accurate long-range tracking becomes less important with the ending of the cold war, and less-expensive ground based radars are once again being looked at for roles such as maritime reconnaissance and drug enforcement. This long range Radar antenna, known as ALTAIR, is used to detect and track space objects in conjunction with ABM testing at the Ronald Reagan Test Site on the Kwajalein atoll[1]. Radar is a system that uses radio waves to determine and map the location, direction, and/or speed... An early warning radar is any radar system used primarily for the long-range detection of its selected targets. ... United States Air Force E-3 Sentry An Airborne Early Warning (AEW) system is a radar system carried by an aircraft which is designed to detect other aircraft. ... For other uses, see Cold War (disambiguation). ...


Radio waves, a form of electromagnetic radiation, tend to travel in straight lines. This generally limits the detection range of radar systems to objects on their horizon due to the curvature of the Earth. For example, a radar mounted on top of a 10 metre mast has a range to the horizon of about 13,000 m, taking into account atmospheric refraction effects. If the target is above the surface this range will be increased accordingly, so a target 10 metres high can be detected by the same radar at 26 km. In general it is impractical to build radar systems with line-of-sight ranges beyond a few hundred kilometers. OTH radars use various techniques to see beyond the horizon, making them particularly useful in the early warning radar role. Electromagnetic radiation can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. ... An early warning radar is any radar system used primarily for the long-range detection of its selected targets. ...


The most common method of constructing an OTH radar is the use of ionospheric reflection. Only one range of frequencies regularly exhibits this behaviour: the high frequency (HF) or shortwave part of the spectrum from 3 – 30 MHz. Given certain conditions in the atmosphere, radio signals in this frequency range will be reflected back towards the ground. The "correct" frequency to use depends on the current conditions of the atmosphere, so systems using ionospheric reflection typically uses real-time monitoring of the reception of backscattered signals to continuously adjust the frequency of the transmitted signal. Relationship of the atmosphere and ionosphere The ionosphere is the part of the atmosphere that is ionized by solar radiation. ... High frequency (HF) radio frequencies are between 3 and 30 MHz. ... A solid-state, analog shortwave receiver Shortwave radio operates between the frequencies of 3,000 kHz and 30 MHz (30,000 kHz) [1] and came to be referred to as such in the early days of radio because the wavelengths associated with this frequency range were shorter than those commonly... It has been suggested that this article or section be merged with Radio waves. ...


After reflection off the atmosphere, a small amount of the signal will reflect off the ground back towards the sky, and a small proportion of that back towards the broadcaster. Given the losses at each reflection, this "backscatter" signal is extremely small, which is one reason why OTH radars were not practical until the 1960s, when extremely low-noise amplifiers were first being designed.


Since the ground and sea will also reflect these signals, some system needs to be used to distinguish the "targets" from the background noise. The easiest way to do this is to use the Doppler effect, which causes moving targets to shift the returned signal's frequency. By filtering out all the backscatter signal close to the original transmitted frequency, moving targets become visible. This basic concept is used in almost all modern radars, but in the case of OTH systems it becomes considerably more complex due to similar effects introduced by movement of the ionosphere. A source of waves moving to the left. ...


The resolution of any radar depends on the width of the beam and the range to the target. For example a radar with a 1/2 degree beamwidth with a target at 120 km range will show the target as 1 km wide. Because of the long ranges at which OTH radars are used, the resolution is typically measured in tens of kilometres. This makes the backscatter system almost useless for target engagement, although this sort of accuracy is adequate for the early warning role. In order to achieve a beamwidth of 1/2 degree at HF an antenna array several kilometres long is required.


Much of the early research into OTH systems was carried out under the direction of Dr. William J. Thaler at the Naval Research Laboratory; The work was dubbed "Project Teepee" (Thaler's project). Their first experimental system, MUSIC (Multiple Storage, Integration, and Correlation), became operational in 1955 and was able to detect rocket launches 600 miles away at Cape Canaveral, and nuclear explosions in Nevada at 1,700 miles. A greatly improved system, a testbed for an operational radar, was later built in 1961 as MADRE (Magnetic-Drum Radar Equipment) at Chesapeake Bay. As the names imply, both systems relied on the comparison of returned signals stored on magnetic drums, then the only high-speed storage systems available.-1... Cape Canaveral from space, August 1991 Cape Canaveral (Cabo Cañaveral in Spanish) is a strip of land in Brevard County, Florida, United States, near the center of that states Atlantic coast. ... This article does not adequately cite its references or sources. ... The Chesapeake Bay - Landsat photo The Chesapeake Bay where the Susquehanna River empties into it. ... The Magnetic Drum was invented by G. Taushek in 1932 in Austria. ...


The first truly operational development was an Anglo-American experiment known as Cobra Mist. Built starting in the late 1960s, Cobra Mist used an enormous 10 MW transmitter and could detect aircraft over the western USSR from its location in Suffolk. When the system started testing in 1972, however, an unexpected source of noise proved to render it unusable. They eventually abandoned the site in 1973, the source of the noise never having been identified. Suffolk (pronounced ) is a large historic and modern non-metropolitan county in East Anglia, England. ...

OTH-B coverage from stations in Maine and Oregon.
OTH-B coverage from stations in Maine and Oregon.

The USAF's Rome Laboratory tried again with their AN/FPS-118 OTH-B. A prototype with a 1 MW transmitter and a separate receiver was installed in Maine, offering coverage over a 60 degree arc between 900 to 3,300 km. The coverage could be extended with additional receivers, providing for complete coverage over a 180 degree arc (each 60 degree portion known as a "sector"). GE Aerospace was awarded the development contract, expanding the existing east coast system with two additional sectors, while building another three-sector system on the west coast, a two-sector system in Alaska, and a one-sector system facing south. In 1992 the Air Force contracted to extend the coverage 15 degrees clockwise on the southern of the three east coast sectors to be able to cover the southeast US border. This was operated 40 hours a week at random times. But the influence from the Senators from Maine were not enough to save the operation and with the ending of the cold war the Alaska and southern-facing sites were cancelled, the two so-far completed western sectors and the eastern ones were turned off and placed in "warm storage," allowing them to be used again if needed. [1] Seal of the Air Force. ... The Rome Laboratory, formerly known as the Rome Air Development Center, is a research and development lab run by the US Air Force located at Griffiss AFB in Rome, NY. One of four superlabs run by the Air Force, the Rome Lab is tasked with generic research, as opposed to... GE redirects here. ... Official language(s) English Capital Juneau Largest city Anchorage Area  Ranked 1st  - Total 663,267 sq mi (1,717,855 km²)  - Width 808 miles (1,300 km)  - Length 1,479 miles (2,380 km)  - % water 13. ... For other uses, see Cold War (disambiguation). ...


The US Navy also created their own system, the AN/TPS-71 ROTHR (Relocatable Over-the-Horizon Radar), which covers a 64 degree wedge-shaped area at ranges between 500 to 1,600 nautical miles (925 to 3,000 km). ROTHR was originally intended to keep track of ship and aircraft movement over the Atlantic, and thus allow coordinated fleet movements well in advance of an engagement. A prototype ROTHR system was installed on the isolated Aleutian Island of Amchitka, Alaska, monitoring the eastern coast of Russia, in 1991 and used until 1993, but was later moved to Virginia where it is used to counter the illegal drug trade, covering Central America and the Caribbean. A second ROTHR was later set up in Texas, covering many of the same areas in the Atlantic, but also providing coverage over the Pacific as far south as Colombia. It also operates in the drug trafficking role. The United States Navy (USN) is the branch of the United States armed forces responsible for naval operations. ... A nautical mile is a unit of distance, or, as physical scientists like to call it, length. ... These lollipops were found to contain heroin when inspected by the US DEA The illegal drug trade is a worldwide black market consisting of production, distribution, packaging and sale of illegal psychoactive substances. ... Map of Central America Central America is the central geographic region of the Americas. ... West Indian redirects here. ...


The Soviets also operated an OTH system between 1976 and 1989. It was designated "Steel Yard" by NATO, but its loud and repetitive pulses in the middle of the shortwave radio bands led to it being known as the Russian Woodpecker by amateur radio (ham) operators. Upset by the interference, some amateur operators attempted to jam it by transmitting 'dots' from automatic morse keyers on the same frequency, although it is not clear if this had the desired effect. The Soviets eventually shifted the frequencies they used, without admitting they were even the source, largely due to its interference with certain long-range air-to-ground communications used by commercial airliners. Soviet redirects here. ... NATO 2002 Summit in Prague. ... A solid-state, analog shortwave receiver Shortwave radio operates between the frequencies of 3,000 kHz and 30 MHz (30,000 kHz) [1] and came to be referred to as such in the early days of radio because the wavelengths associated with this frequency range were shorter than those commonly... The Russian Woodpecker was a notorious Soviet signal that could be heard on the shortwave radio bands worldwide between July 1976 and December 1989. ... Ham radio station with modern solid-state transceiver featuring LCD display and DSP capabilities Ham radio station with vintage vacuum tube gear featuring separate transmitter, receiver and power supply Amateur radio, often called Ham radio, is a hobby and public service enjoyed by about 6 million people throughout the world. ... Radar jamming is the intentional emission of radio frequency signals to interfere with the operation of a radar by saturating its receiver with false information. ...


A more recent addition is the Jindalee over-the-horizon radar developed by the Australian Department of Defence in 1998 and completed in 2000. Jindalee is a multistatic radar (multiple-receiver) system using OTH-B, allowing it to have both long range as well as anti-stealth capabilities. Interestingly, Jindalee uses 560 kW as compared to the US's OTH-B's 1 MW, yet offers far better range due to considerably improved electronics and signal processing.[1] The area JORN operates in. ... In a multistatic radar system the transmitter and receiver are positioned in different locations. ... F-117 Stealth Fighter Stealth technology covers a range of techniques used with aircraft, ships and missiles, in order to make them less visible (ideally invisible) to radar, infrared and other detection methods. ...


An entirely different approach to over-the-horizon radar is to use creeping waves at much lower frequencies. Creeping waves are the scattering into the rear of an object due to diffraction, which is the reason both ears can hear a sound on one side of the head, for instance, and was how early communication and broadcast radio was accomplished. In the radar role, the creeping waves in question are diffracting around the Earth itself, although processing the returned signal is quite difficult. Development of such systems became practical in the late 1980s due to the rapidly increasing processing power available. Such systems are known as OTH-SW, for Surface Wave. According to the principle of diffraction, when a wave front passes an obstruction, it spreads out into the shadowed space. ... The intensity pattern formed on a screen by diffraction from a square aperture Diffraction refers to various phenomena associated with wave propagation, such as the bending, spreading and interference of waves passing by an object or aperture that disrupts the wave. ...


The first OTH-SW system deployed appears to be a Soviet system positioned to watch traffic in the Sea of Japan, while a newer system has recently been used for coastal surveillance in Canada. Australia has also deployed a High Frequency Surface Wave Radar[2]. The Sea of Japan (East Sea) is a marginal sea of the western Pacific Ocean. ...


References

  1. ^ Colegrove, Samuel B.(Bren) (2000). "Project Jindalee: From Bare Bones To Operational OTHR". IEEE International Radar Conference - Proceedings: 825-830, IEEE. Retrieved on 2006-11-17. 
  2. ^ Senator Robert Hill, Landmark Land Use Agreement For High Frequency Surface Radar, Ministerial Press Release number 33/2004 from the Australian Department of Defence, February 25, 2004

For the Manfred Mann album, see 2006 (album). ... 17 November is also the name of a Marxist group in Greece, coinciding with the anniversary of the Athens Polytechnic uprising. ... Senator Robert Hill Robert Murray Hill (born 25 September 1946), Australian politician, was a Liberal member of the Australian Senate from July 1981 to January 2006, representing South Australia. ...

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