Over-the-horizon radar
Encyclopedia
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 1950s and 60s 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systems, but these have generally been replaced by airborne early warning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.
, 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 m (32.8 ft) mast has a range to the horizon of about 13 kilometres (8.1 mi), taking into account atmospheric refraction effects. If the target is above the surface this range will be increased accordingly, so a target 10 m (32.8 ft) high can be detected by the same radar at 26 km (16.2 mi). 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.
The most common method of constructing an OTH radar is the use of ionospheric
reflection. Given certain conditions in the atmosphere, radio signals broadcast up towards the ionosphere will be reflected back towards the ground. 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. 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 employ real-time monitoring of the reception of backscattered signals to continuously adjust the frequency of the transmitted signal.
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 signal reflected from the ground, or sea, will be very large compared to the signal reflected from a "target", 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 uses frequency shift created by moving objects to measure their velocity. 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 itself.
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 and a target at 120 km (74.6 mi) range will show the target as 1 km (0.621372736649807 mi) wide. Because of the long ranges at which OTH radars are used, the resolution is typically measured in tens of kilometers. This makes the backscatter system almost useless for target engagement, although this sort of accuracy is more than adequate for the early warning role. In order to achieve a beamwidth of 1/2 degree at HF, an antenna array several kilometers long is required.
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 (965.6 km) away at Cape Canaveral
, and nuclear explosions in Nevada
at 1700 miles (2,735.9 km). 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.
The first truly operational development was an Anglo-American system 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.
The Soviets were also working on similar systems during this time, and started operation of their own experimental system in 1971. This was followed shortly thereafter by the first operational system, known in the west as Steel Yard, which started operation in 1976.
The USAF's Rome Laboratory
had the first US success 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. A permanent transmitting facility was then built at Moscow AFS
, a receiving facility at Columbia Falls AFS
, and an operational center between them in Bangor
. 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. Additionally, the range was extended to 3000 miles (4,828 km), crossing the equator. This was operated 40 hours a week at random times. Radar data was fed to the U.S. Customs/Coast Guard C3I Center, Miami; Joint Task Force 4 Operations Center, Key West; U.S. Southern Command Operations Center, Key West; and U.S. Southern Command Operations Center, Panama.
With the end of the cold war
, the influence of the two senators from Maine
was not enough to save the operation and the Alaska and southern-facing sites were canceled, 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.
By 2002, the west coast facilities were downgraded to "cold storage" status, meaning only minimal maintenance was performed by a caretaker. Research was begun into the feasibility of removing the facilities. After a period of public input and environmental studies, in July 2005 the U.S. Air Force Air Combat Command published a "Final Environmental Assessment for Equipment Removal at Over-the-Horizon Backscatter Radar - West Coast Facilities" .
A final decision was made to remove all radar equipment at the west coast sector's transmitter site outside Christmas Valley, Oregon
and its receiver site near Tulelake, California
. This work was completed by July 2007 with the demolition and removal of the antenna arrays, leaving the buildings, fences and utility infrastructure at each site intact.
, covering Central America
and the Caribbean
. The second production ROTHR was later set up in Texas, covering many of the same areas in the Caribbean, but also providing coverage over the Pacific as far south as Colombia
. It also operates in the anti-drug trafficking role. The third, and final, production system was installed in Puerto Rico, extending counterdrug surveillance past the equator, deep into South America.
coast near Odessa
). Aimed eastward, Duga-2 was first started on 7 November 1971, and was successfully used to track missile launches from the far east and Pacific Ocean to the testing ground on Novaya Zemlya
.
This was followed by their first operational system, known in the west as Steel Yard, which first broadcast in 1976. Built outside Gomel, near Chernobyl, it was aimed northward and covered the continental USA. 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. 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. A second system was set up in Siberia, also covering the continental USA, as well as Alaska.
developed by the Australia
n Department of Defence in 1998 and completed in 2000. It is operated by No. 1 Radar Surveillance Unit
of the Royal Australian Air Force
. Jindalee is a multistatic radar
(multiple-receiver) system using OTH-B, allowing it to have both long range as well as anti-stealth
capabilities. It has an official range of 3000 kilometres (1,864.1 mi) but in 1997 the prototype was able to detect missile launches by China
over 5500 kilometres (3,417.6 mi) away.
Jindalee uses 560 kW as compared to the US's OTH-B's 1 MW, yet offers far better range than the US 1980s system, due to the considerably improved electronics and signal processing.
have developed an OTH radar called NOSTRADAMUS (stands for New Transhorizon Decametric System Applying Studio Methods) during the 1990s. It entered in service for the French army in 2005, but is still in development. It is based on a star shaped antenna field used for emission and reception (monostatic) able to detect every aircraft at more than one thousand kilometers, in a 360 degree arc. The frequency range used is from 6 to 30 MHz.
s or electromagnetic surface 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.
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.
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
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 1950s and 60s as part of early warning radar
Early warning radar
An early warning radar is any radar system used primarily for the long-range detection of its targets, i.e., allowing defences to be alerted as early as possible before the intruder reaches its target, giving the defences the maximum time in which to operate...
systems, but these have generally been replaced by airborne early warning
Airborne Early Warning
An airborne early warning and control system is an airborne radar system designed to detect aircraft at long ranges and control and command the battle space in an air engagement by directing fighter and attack plane strikes...
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
Cold War
The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...
, and less-expensive ground based radars are once again being looked at for roles such as maritime reconnaissance and drug enforcement.
Technology
Radio waves, a form of electromagnetic radiationElectromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
, tend to travel in straight lines. This generally limits the detection range of radar systems to objects on their horizon
Radar horizon
The radar Horizon is a critical area of performance for aircraft detection systems that is defined by the distance at which the radar beam raise enough above the Earth surface to make detection of a target at low level impossible. It is associated with the low elevation region of performance and...
due to the curvature of the Earth. For example, a radar mounted on top of a 10 m (32.8 ft) mast has a range to the horizon of about 13 kilometres (8.1 mi), taking into account atmospheric refraction effects. If the target is above the surface this range will be increased accordingly, so a target 10 m (32.8 ft) high can be detected by the same radar at 26 km (16.2 mi). 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
Early warning radar
An early warning radar is any radar system used primarily for the long-range detection of its targets, i.e., allowing defences to be alerted as early as possible before the intruder reaches its target, giving the defences the maximum time in which to operate...
role.
The most common method of constructing an OTH radar is the use of ionospheric
Ionosphere
The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...
reflection. Given certain conditions in the atmosphere, radio signals broadcast up towards the ionosphere will be reflected back towards the ground. 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. Only one range of frequencies regularly exhibits this behaviour: the high frequency
High frequency
High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...
(HF) or shortwave
Shortwave
Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...
part of the spectrum
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
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 employ real-time monitoring of the reception of backscattered signals to continuously adjust the frequency of the transmitted signal.
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 signal reflected from the ground, or sea, will be very large compared to the signal reflected from a "target", 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
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
, which uses frequency shift created by moving objects to measure their velocity. 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 itself.
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 and a target at 120 km (74.6 mi) range will show the target as 1 km (0.621372736649807 mi) wide. Because of the long ranges at which OTH radars are used, the resolution is typically measured in tens of kilometers. This makes the backscatter system almost useless for target engagement, although this sort of accuracy is more than adequate for the early warning role. In order to achieve a beamwidth of 1/2 degree at HF, an antenna array several kilometers long is required.
History
Much of the early research into effective OTH systems was carried out under the direction of Dr. William J. ThalerWilliam J. Thaler
William J. Thaler, Ph.D. was an American experimental physicist. Working for the Office of Naval Research at the Naval Research Laboratory in the 1950s, Thaler developed an early warning system to detect the launching of ballistic missiles using high frequency radio waves bounced between the...
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 (965.6 km) away at Cape Canaveral
Cape Canaveral
Cape Canaveral, from the Spanish Cabo Cañaveral, is a headland in Brevard County, Florida, United States, near the center of the state's Atlantic coast. Known as Cape Kennedy from 1963 to 1973, it lies east of Merritt Island, separated from it by the Banana River.It is part of a region known as the...
, and nuclear explosions in Nevada
Nevada
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...
at 1700 miles (2,735.9 km). A greatly improved system, a testbed for an operational radar, was later built in 1961 as MADRE (Magnetic-Drum Radar Equipment) at Chesapeake Bay
Chesapeake Bay
The Chesapeake Bay is the largest estuary in the United States. It lies off the Atlantic Ocean, surrounded by Maryland and Virginia. The Chesapeake Bay's drainage basin covers in the District of Columbia and parts of six states: New York, Pennsylvania, Delaware, Maryland, Virginia, and West...
. 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.
The first truly operational development was an Anglo-American system known as Cobra Mist
Cobra Mist
Cobra Mist was the codename for an Anglo-American experimental over-the-horizon radar station at Orford Ness, Suffolk, England . It was known technically as AN/FPS-95 and sometimes referred to as System 441a; a reference to the project as a whole. Cobra Mist was part of a small number of "Cobra"...
. 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
Suffolk
Suffolk is a non-metropolitan county of historic origin in East Anglia, England. It has borders with Norfolk to the north, Cambridgeshire to the west and Essex to the south. The North Sea lies to the east...
. 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.
The Soviets were also working on similar systems during this time, and started operation of their own experimental system in 1971. This was followed shortly thereafter by the first operational system, known in the west as Steel Yard, which started operation in 1976.
USAF
Rome Laboratory
The Rome Laboratory, formerly known as the Rome Air Development Center, is one of eight research and development labs 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 having a...
had the first US success with their AN/FPS-118 OTH-B. A prototype with a 1 MW transmitter and a separate receiver was installed in Maine
Maine
Maine is a state in the New England region of the northeastern United States, bordered by the Atlantic Ocean to the east and south, New Hampshire to the west, and the Canadian provinces of Quebec to the northwest and New Brunswick to the northeast. Maine is both the northernmost and easternmost...
, offering coverage over a 60 degree arc between 900 to 3,300 km. A permanent transmitting facility was then built at Moscow AFS
Moscow Air Force Station
Moscow Air Force Station is a closed United States Air Force radar station in Somerset County, Maine. Located northeast of Moscow, Maine, it went operational in 1990 but was closed in 1997 and placed in "warm storage" with minimal maintenance...
, a receiving facility at Columbia Falls AFS
Columbia Falls Air Force Station
Columbia Falls Air Force Station is a closed United States Air Force radar station in Washington County, Maine. Located northwest of Machias, Maine and north of Columbia Falls, it went operational in 1990 but was closed in 1997 and placed in "warm storage" with minimal maintenance...
, and an operational center between them in Bangor
Bangor, Maine
Bangor is a city in and the county seat of Penobscot County, Maine, United States, and the major commercial and cultural center for eastern and northern Maine...
. 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
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
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
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
, 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. Additionally, the range was extended to 3000 miles (4,828 km), crossing the equator. This was operated 40 hours a week at random times. Radar data was fed to the U.S. Customs/Coast Guard C3I Center, Miami; Joint Task Force 4 Operations Center, Key West; U.S. Southern Command Operations Center, Key West; and U.S. Southern Command Operations Center, Panama.
With the end of the cold war
Cold War
The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...
, the influence of the two senators from Maine
Maine
Maine is a state in the New England region of the northeastern United States, bordered by the Atlantic Ocean to the east and south, New Hampshire to the west, and the Canadian provinces of Quebec to the northwest and New Brunswick to the northeast. Maine is both the northernmost and easternmost...
was not enough to save the operation and the Alaska and southern-facing sites were canceled, 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.
By 2002, the west coast facilities were downgraded to "cold storage" status, meaning only minimal maintenance was performed by a caretaker. Research was begun into the feasibility of removing the facilities. After a period of public input and environmental studies, in July 2005 the U.S. Air Force Air Combat Command published a "Final Environmental Assessment for Equipment Removal at Over-the-Horizon Backscatter Radar - West Coast Facilities" .
A final decision was made to remove all radar equipment at the west coast sector's transmitter site outside Christmas Valley, Oregon
Christmas Valley, Oregon
Christmas Valley is an unincorporated community in Lake County, Oregon, United States. The community was named after nearby dry Christmas Lake, east of the present townsite and the site of the former Lake post office, which ran from 1906 until 1943. Real estate development around a planned...
and its receiver site near Tulelake, California
Tulelake, California
Tulelake is a city in Siskiyou County, California, United States. It is named after the nearby Tule Lake. The population was 1,010 at the 2010 census, down from 1,020 at the 2000 census.-Geography:Tulelake is located at ....
. This work was completed by July 2007 with the demolition and removal of the antenna arrays, leaving the buildings, fences and utility infrastructure at each site intact.
US Navy
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 Pacific, 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. The equipment was later removed into storage. The first production systems were installed in the test site in Virginia for acceptance testing but were then transitioned to counter the illegal drug tradeIllegal drug trade
The illegal drug trade is a global black market, dedicated to cultivation, manufacture, distribution and sale of those substances which are subject to drug prohibition laws. Most jurisdictions prohibit trade, except under license, of many types of drugs by drug prohibition laws.A UN report said the...
, covering Central America
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
and the Caribbean
Caribbean
The Caribbean is a crescent-shaped group of islands more than 2,000 miles long separating the Gulf of Mexico and the Caribbean Sea, to the west and south, from the Atlantic Ocean, to the east and north...
. The second production ROTHR was later set up in Texas, covering many of the same areas in the Caribbean, but also providing coverage over the Pacific as far south as Colombia
Colombia
Colombia, officially the Republic of Colombia , is a unitary constitutional republic comprising thirty-two departments. The country is located in northwestern South America, bordered to the east by Venezuela and Brazil; to the south by Ecuador and Peru; to the north by the Caribbean Sea; to the...
. It also operates in the anti-drug trafficking role. The third, and final, production system was installed in Puerto Rico, extending counterdrug surveillance past the equator, deep into South America.
USSR/Russia
The Soviets had also studied OTH systems starting as early as the 1950s. Their first experimental model appears to be the Veyer (Hand Fan) that was built in 1949. The next serious Soviet project was Duga-2, built outside Nikolayev (on the Black SeaBlack Sea
The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...
coast near Odessa
Odessa
Odessa or Odesa is the administrative center of the Odessa Oblast located in southern Ukraine. The city is a major seaport located on the northwest shore of the Black Sea and the fourth largest city in Ukraine with a population of 1,029,000 .The predecessor of Odessa, a small Tatar settlement,...
). Aimed eastward, Duga-2 was first started on 7 November 1971, and was successfully used to track missile launches from the far east and Pacific Ocean to the testing ground on Novaya Zemlya
Novaya Zemlya
Novaya Zemlya , also known in Dutch as Nova Zembla and in Norwegian as , is an archipelago in the Arctic Ocean in the north of Russia and the extreme northeast of Europe, the easternmost point of Europe lying at Cape Flissingsky on the northern island...
.
This was followed by their first operational system, known in the west as Steel Yard, which first broadcast in 1976. Built outside Gomel, near Chernobyl, it was aimed northward and covered the continental USA. Its loud and repetitive pulses in the middle of the shortwave
Shortwave
Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...
radio bands led to it being known as the Russian Woodpecker
Russian Woodpecker
The Russian Woodpecker was a notorious Soviet signal that could be heard on the shortwave radio bands worldwide between July 1976 and December 1989. It sounded like a sharp, repetitive tapping noise, at 10 Hz, giving rise to the "Woodpecker" name...
by amateur radio
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
(ham) operators. 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. A second system was set up in Siberia, also covering the continental USA, as well as Alaska.
Australia
A more recent addition is the Jindalee Operational Radar NetworkJindalee Operational Radar Network
The Jindalee Operational Radar Network is an over-the-horizon radar network that can monitor air and sea movements across 37,000 km2. It has an official range of 3,000 km. It is used in the defence of Australia and can also monitor maritime operations, wave heights and wind directions...
developed by the Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
n Department of Defence in 1998 and completed in 2000. It is operated by No. 1 Radar Surveillance Unit
No. 1 Radar Surveillance Unit RAAF
No. 1 Radar Surveillance Unit is the Royal Australian Air Force unit responsible for operating the Jindalee Operational Radar Network...
of the Royal Australian Air Force
Royal Australian Air Force
The Royal Australian Air Force is the air force branch of the Australian Defence Force. The RAAF was formed in March 1921. It continues the traditions of the Australian Flying Corps , which was formed on 22 October 1912. The RAAF has taken part in many of the 20th century's major conflicts...
. Jindalee is a multistatic radar
Multistatic radar
A multistatic radar system contains multiple spatially diverse monostatic radar or bistatic radar components with a shared area of coverage. An important distinction systems based on these individual radar geometries is the added requirement for some level of data fusion to take place between...
(multiple-receiver) system using OTH-B, allowing it to have both long range as well as anti-stealth
Stealth technology
Stealth technology also termed LO technology is a sub-discipline of military tactics and passive electronic countermeasures, which cover a range of techniques used with personnel, aircraft, ships, submarines, and missiles, to make them less visible to radar, infrared, sonar and other detection...
capabilities. It has an official range of 3000 kilometres (1,864.1 mi) but in 1997 the prototype was able to detect missile launches by China
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...
over 5500 kilometres (3,417.6 mi) away.
Jindalee uses 560 kW as compared to the US's OTH-B's 1 MW, yet offers far better range than the US 1980s system, due to the considerably improved electronics and signal processing.
France
The FrenchFrance
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
have developed an OTH radar called NOSTRADAMUS (stands for New Transhorizon Decametric System Applying Studio Methods) during the 1990s. It entered in service for the French army in 2005, but is still in development. It is based on a star shaped antenna field used for emission and reception (monostatic) able to detect every aircraft at more than one thousand kilometers, in a 360 degree arc. The frequency range used is from 6 to 30 MHz.
China
A number of OTH-B and OTH-SW radars are reportedly in operation in China. However, few details are known of these systems.Alternate OTH approaches
An entirely different approach to over-the-horizon radar is to use creeping waveCreeping wave
According to the principle of diffraction, when a wave front passes an obstruction, it spreads out into the shadowed space. A creeping wave, in electromagnetism or acoustics is the wave that is diffracted around the shadowed surface of a smooth body such as a sphere.Creeping waves greatly extend...
s or electromagnetic surface waves at much lower frequencies. Creeping waves are the scattering into the rear of an object due to diffraction
Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...
, 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.
The first OTH-SW system deployed appears to be a Soviet system positioned to watch traffic in the Sea of Japan
Sea of Japan
The Sea of Japan is a marginal sea of the western Pacific Ocean, between the Asian mainland, the Japanese archipelago and Sakhalin. It is bordered by Japan, North Korea, Russia and South Korea. Like the Mediterranean Sea, it has almost no tides due to its nearly complete enclosure from the Pacific...
, while a newer system has recently been used for coastal surveillance in Canada. Australia has also deployed a High Frequency Surface Wave Radar.
External links
- A Canadian Perspective on High-Frequency Over-the-Horizon Radar - paper by R. J. Riddolls Defence R&D Canada – Ottawa
- The Development of Over-the-Horizon Radar in Australia - paper by D.H. Sinnott on the Australian Department of Defence website
- Google maps link - Russian "Steel-Yard" radar near ChernobylChernobylChernobyl or Chornobyl is an abandoned city in northern Ukraine, in Kiev Oblast, near the border with Belarus. The city had been the administrative centre of the Chernobyl Raion since 1932....
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