![OTH-B](https://upload.wikimedia.org/wikipedia/commons/3/3d/OTH-B.big.jpg)
Over-the-horizon radar (OTH), sometimes called beyond the horizon radar (BTH), is a type of
radar
Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
system with the ability to detect targets at very long ranges, typically hundreds to thousands of kilometres, beyond the
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 rises enough above the Earth's surface to make detection of a target at low level impossible. It is associ ...
, which is the distance limit for ordinary
radar
Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
. Several OTH radar systems were deployed starting in the 1950s and 1960s as part of
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 air defences the maximum t ...
systems, but these have generally been replaced by
airborne early warning
Airborne or Airborn may refer to:
Arts, entertainment, and media
Films
* ''Airborne'' (1962 film), a 1962 American film directed by James Landis
* ''Airborne'' (1993 film), a comedy–drama film
* ''Airborne'' (1998 film), an action film sta ...
systems. OTH radars have recently been making a comeback, as the need for accurate long-range tracking becomes less important with the ending of the
Cold War
The Cold War is a term commonly used to refer to a period of geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc. The term '' cold war'' is used because the ...
, and less-expensive ground-based radars are once again being considered for roles such as maritime reconnaissance and drug enforcement.
Technology
The frequency of
radio wave
Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (short ...
s used by most radars, in the form of
microwave
Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ran ...
s, travel in straight lines. This generally limits the detection range of radar systems to objects on their
horizon
The horizon is the apparent line that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This line divides all viewing directions based on whether i ...
(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. For example, a radar mounted on top of a mast has a range to the horizon of about , taking into account atmospheric refraction effects. If the target is above the surface, this range will be increased accordingly, so a target high can be detected by the same radar at . Siting the antenna on a high mountain can increase the range somewhat; but, in general, it is impractical to build radar systems with line-of-sight ranges beyond a few hundred kilometres.
OTH radars use various techniques to see beyond that limit. Two techniques are most commonly used; shortwave systems that refract their signals off the
ionosphere
The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an ...
for very long-range detection, and
surface wave
In physics, a surface wave is a mechanical wave that propagates along the Interface (chemistry), interface between differing media. A common example is gravity waves along the surface of liquids, such as ocean waves. Gravity waves can also occu ...
systems, which use low frequency radio waves that, due to
diffraction
Diffraction is defined as the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a s ...
, follow the curvature of the Earth to reach beyond the horizon. These systems achieve detection ranges of the order of a hundred kilometres from small, conventional radar installations. They can scan a series of high frequencies using a
chirp transmitter
An ionosonde, or chirpsounder, is a special radar for the examination of the ionosphere. The basic ionosonde technology was invented in 1925 by Gregory Breit and Merle A. Tuve and further developed in the late 1920s by a number of prominent ph ...
.
Skywave systems
![ROTHR USNavy b](https://upload.wikimedia.org/wikipedia/commons/d/d6/ROTHR_USNavy_b.png)
The most common type of OTH radar uses
skywave
In radio communication, skywave or skip refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere. Since it is not limited by the curvature of ...
or "skip" propagation, in which
shortwave
Shortwave radio is radio transmission using shortwave (SW) radio frequencies. There is no official definition of the band, but the range always includes all of the high frequency band (HF), which extends from 3 to 30 MHz (100 to 10 me ...
radio waves are refracted off an
ionized
Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule ...
layer in the atmosphere, the
ionosphere
The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an ...
. Given certain conditions in the atmosphere, radio signals transmitted at an angle into the sky will be refracted towards the ground by the
ionosphere
The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an ...
, allowing them to return to earth beyond the horizon. A small amount of this signal will be scattered off desired targets back towards the sky, refracted off the ionosphere again, and return to the receiving antenna by the same path. Only one range of frequencies regularly exhibits this behaviour: the
high frequency (HF) or
shortwave
Shortwave radio is radio transmission using shortwave (SW) radio frequencies. There is no official definition of the band, but the range always includes all of the high frequency band (HF), which extends from 3 to 30 MHz (100 to 10 me ...
part of the
spectrum
A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...
from 3–30 MHz. The best frequency to use depends on the current conditions of the atmosphere and the
sunspot cycle
The solar cycle, also known as the solar magnetic activity cycle, sunspot cycle, or Schwabe cycle, is a nearly periodic 11-year change in the Sun's activity measured in terms of variations in the number of observed sunspots on the Sun's surfac ...
. For these reasons, systems using skywaves typically employ real-time monitoring of the reception of backscattered signals to continuously adjust the frequency of the transmitted signal.
The resolution of any radar depends on the width of the beam and the range to the target. For example; a radar with 1 degree beam width and a target at range will show the target as wide. To produce a 1-degree beam at the most common frequencies, an antenna wide is required. Due to the physics of the refraction process, actual accuracy is even lower, with range resolution on the order of and bearing accuracy of being suggested. Even a 2 km accuracy is useful only for early warning, not for weapons fire.
Another problem is that the refraction process is highly dependent on the angle between the signal and the ionosphere, and is generally limited to about 2–4 degrees off the local horizon. Making a beam at this angle generally requires enormous antenna arrays and highly reflective ground along the path the signal is being sent, often enhanced by the installation of wire mesh mats extending as much as in front of the antenna. OTH systems are thus very expensive to build, and essentially immobile.
Given the losses at each refraction, 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 refracted from the ground, or sea, will be very large compared to the signal refracted 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
The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who d ...
, 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. Even a small amount of movement can be seen using this process, speeds as low as .
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. Most systems used a second transmitter broadcasting directly up at the ionosphere to measure its movement and adjust the returns of the main radar in real-time. Doing so required the use of
computer
A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as C ...
s, another reason OTH systems did not become truly practical until the 1960s, with the introduction of
solid-state
Solid state, or solid matter, is one of the four fundamental states of matter.
Solid state may also refer to:
Electronics
* Solid-state electronics, circuits built of solid materials
* Solid state ionics, study of ionic conductors and their use ...
high-performance systems.
Ground wave systems
A second type of OTH radar uses much lower frequencies, in the
longwave
In radio, longwave, long wave or long-wave, and commonly abbreviated LW, refers to parts of the radio spectrum with wavelengths longer than what was originally called the medium-wave broadcasting band. The term is historic, dating from the e ...
bands. Radio waves at these frequencies can diffract around obstacles and follow the curving contour of the earth, traveling beyond the horizon. Echos reflected off the target return to the transmitter location by the same path. These ''
ground wave
Ground waves are radio waves propagating parallel to and adjacent to the surface of the Earth, following the curvature of the Earth. This radiation is known as Norton surface wave, or more properly Norton ground wave, because ground waves in rad ...
s'' have the longest range over the sea. Like the ionospheric high-frequency systems, the received signal from these ground wave systems is very low, and demands extremely sensitive electronics. Because these signals travel close to the surface, and lower frequencies produce lower resolutions, low-frequency systems are generally used for tracking ships, rather than aircraft. However, the use of
bistatic techniques and computer processing can produce higher resolutions, and has been used beginning in the 1990s.
History
Engineers in the
Soviet Union
The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen national ...
are known to have developed what appears to be the first operational OTH system in 1949, called "Veyer". However, little information on this system is available in western sources, and no details of its operation are known. It is known that no further research was carried out by Soviet teams until the 1960s and 70s.
Much of the early research into effective OTH systems was carried out under the direction of Dr.
William J. Thaler at the
Naval Research Laboratory
The United States Naval Research Laboratory (NRL) is the corporate research laboratory for the United States Navy and the United States Marine Corps. It was founded in 1923 and conducts basic scientific research, applied research, technological ...
. The work was dubbed "Project Teepee" (for "Thaler's Project"). Their first experimental system, MUSIC (''Multiple Storage, Integration, and Correlation''), became operational in 1955 and was able to detect rocket launches away at
Cape Canaveral
, image = cape canaveral.jpg
, image_size = 300
, caption = View of Cape Canaveral from space in 1991
, map = Florida#USA
, map_width = 300
, type =Cape
, map_caption = Location in Florida
, location ...
, and nuclear explosions in
Nevada
Nevada ( ; ) is a U.S. state, state in the Western United States, Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. N ...
at . A greatly improved system, a testbed for an operational radar, was built in 1961 as MADRE (''Magnetic-Drum Radar Equipment'') at
Chesapeake Bay
The Chesapeake Bay ( ) is the largest estuary in the United States. The Bay is located in the Mid-Atlantic (United States), Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula (including the parts: the ...
. It detected aircraft as far as using as little as 50 kW of broadcast energy.
[Laurie states two ranges for MADRE against aircraft, 3000 and 4000 km, on the same page. The former appears to be correct from a comparison with other sources. To add to the confusion, ''Signals'' describes MADRE as having an ''average'' power of 100 kW and a peak of 5 MW, much more powerful than suggested by Laurie. See ''Signals'', Vol 31, Issue 1, p. 7.]
As the names imply, both of the NRL systems relied on the comparison of returned signals stored on
magnetic drum
Drum memory was a magnetic data storage device invented by Gustav Tauschek in 1932 in Austria. Drums were widely used in the 1950s and into the 1960s as computer memory.
For many early computers, drum memory formed the main working memory ...
s. In an attempt to remove
clutter
Clutter and its derivations may refer to any of the following:
Excessive physical disorder
* Clutter, a confusing, or disorderly, state or collection, and possible symptom of compulsive hoarding
* Clutter (marketing), numerous advertisements, a ...
from radar displays, many late-war and post-war radar systems added an
acoustic delay line
Delay-line memory is a form of computer memory, now obsolete, that was used on some of the earliest digital computers. Like many modern forms of electronic computer memory, delay-line memory was a refreshable memory, but as opposed to modern r ...
that stored the received signal for exactly the amount of time needed for the next signal pulse to arrive. By adding the newly arrived signal to an inverted version of the signals stored in the delay line, the output signal included just the ''changes'' from one pulse to the next. This removed any static reflections, like nearby hills or other objects, leaving only the moving objects, such as aircraft. This basic concept would work for a long-range radar as well, but had the problem that a delay line has to be mechanically sized to the
pulse repetition frequency
The pulse repetition frequency (PRF) is the number of pulses of a repeating signal in a specific time unit. The term is used within a number of technical disciplines, notably radar.
In radar, a radio signal of a particular carrier frequency is tu ...
of the radar, or PRF. For long-range use, the PRF was very long to start, and deliberately changed in order to make different ranges come into view. For this role, the delay line was not usable, and the magnetic drum, recently introduced, provided a convenient and easily controlled variable-delay system.
Another early shortwave OTH system was built in
Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
in the early 1960s. This consisted of several antennas positioned to be four wavelengths apart, allowing the system to use phase-shift
beam forming
Beamforming or spatial filtering is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in an antenna array in such a way that signals at particular angles ex ...
to steer the direction of sensitivity and adjust it to cover Singapore, Calcutta and the UK. This system consumed of electrical cable in the antenna array.
Systems
UK/US Cobra Mist
The first truly operational development was an Anglo-American system known as
Cobra Mist
Cobra Mist was the codename for an Anglo-American experimental over-the-horizon radar station at Orford Ness, 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 ...
, which began construction in the late 1960s. Cobra Mist used an enormous 10 MW transmitter and could detect aircraft over the western Soviet Union from its location in
Suffolk
Suffolk () is a ceremonial county of England in East Anglia. It borders Norfolk to the north, Cambridgeshire to the west and Essex to the south; the North Sea lies to the east. The county town is Ipswich; other important towns include Lowes ...
. When system testing started in 1972, however, an unexpected source of noise rendered it largely unusable. The source of the noise was never identified and the site was abandoned in 1973,.
Other early UK/US systems from the same era include:
* an installation at
RAF Akrotiri
RAF Akrotiri ( el, Βασιλική Πολεμική Αεροπορία Ακρωτηρίου) is a large Royal Air Force base on the Mediterranean island of Cyprus. It is located in the Western Sovereign Base Area, one of two areas which compr ...
on
Cyprus
Cyprus ; tr, Kıbrıs (), officially the Republic of Cyprus,, , lit: Republic of Cyprus is an island country located south of the Anatolian Peninsula in the eastern Mediterranean Sea. Its continental position is disputed; while it is geo ...
and
Okinawa
is a prefecture of Japan. Okinawa Prefecture is the southernmost and westernmost prefecture of Japan, has a population of 1,457,162 (as of 2 February 2020) and a geographic area of 2,281 km2 (880 sq mi).
Naha is the capital and largest city ...
. Cobra Shoe was a reported Over The Horizon (Backscatter) (OTH-B) radar designed by
RCA Corporation
The RCA Corporation was a major American electronics company, which was founded as the Radio Corporation of America in 1919. It was initially a patent trust owned by General Electric (GE), Westinghouse, AT&T Corporation and United Fruit Comp ...
, designed to monitor ballistic missile tests in the interior of the Soviet Union, installed in the
Western Sovereign Base Area
Akrotiri and Dhekelia, officially the Sovereign Base Areas of Akrotiri and Dhekelia (SBA),, ''Periochés Kyríarchon Váseon Akrotiríou ke Dekélias''; tr, Ağrotur ve Dikelya İngiliz Egemen Üs Bölgeleri is a British Overseas Territory ...
(Akrotiri),
Cyprus
Cyprus ; tr, Kıbrıs (), officially the Republic of Cyprus,, , lit: Republic of Cyprus is an island country located south of the Anatolian Peninsula in the eastern Mediterranean Sea. Its continental position is disputed; while it is geo ...
. Source is "U.S. declassified documents". Installed since around 1964; no details on when/whether it left service.
* the
Sugar Tree radar system.
U.S. Air Force
![OTH-B coverage](https://upload.wikimedia.org/wikipedia/commons/4/49/OTH-B_coverage.gif)
The
United States Air Force
The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Signal ...
Rome Laboratory
Rome Laboratory (Rome Air Development Center until 1991) is the US "Air Force 'superlab' for command, control, and communications" research and development and is responsible for planning and executing the USAF science and technology program.
...
had the first complete success with their
AN/FPS-118 OTH-B.
[AN/FPS-118 Over-The-Horizon-Backscatter (OTH-B) Radar]
/ref> A prototype with a 1 MW transmitter and a separate receiver was installed in Maine
Maine () is a state in the New England and Northeastern regions of the United States. It borders New Hampshire to the west, the Gulf of Maine to the southeast, and the Canadian provinces of New Brunswick and Quebec to the northeast and north ...
, offering coverage over a 60-degree arc between 900 and 3,300 km. A permanent transmitting facility was then built at Moscow AFS, a receiving facility at 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 ...
, and an operational center between them in Bangor, Maine
Bangor ( ) is a city in the U.S. state of Maine and the county seat of Penobscot County. The city proper has a population of 31,753, making it the state's 3rd-largest settlement, behind Portland (68,408) and Lewiston (37,121).
Modern 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
GE Aviation, a subsidiary of General Electric, is headquartered in Evendale, Ohio, outside Cincinnati. GE Aviation is among the top aircraft engine suppliers, and offers engines for the majority of commercial aircraft. GE Aviation is part of the ...
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 ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S., ...
, 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 U.S. border. Additionally, the range was extended to , crossing the equator. This was operated 40 hours a week at random times. Radar data were fed to the U.S. Customs/Coast Guard C3I Center, Miami; Joint Task Force 4 Operations Center, Key West; U.S. Southern Command
The United States Southern Command (USSOUTHCOM), located in Doral, Florida in Greater Miami, is one of the eleven unified combatant commands in the United States Department of Defense. It is responsible for providing contingency planning, o ...
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 that 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 at Christmas Valley Air Force Station outside ]Christmas Valley, Oregon
Christmas Valley is an unincorporated community in Lake County, Oregon, United States. The community was named after nearby Christmas Lake, usually dry, east of the present town and the site of the former Lake post office, which ran from 1906 un ...
and its receiver site near Tulelake, California
Tulelake ( ) is a city in northeastern Siskiyou County, California, United States. The town is named after nearby Tule Lake. Its population is 902 as of the 2020 census, down from 1,010 from the 2010 census.
Tulelake peace officers are authori ...
. 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.
U.S. Navy
The United States Navy
The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...
created their own system, the AN/TPS-71 ROTHR (Relocatable Over-the-Horizon Radar), which covers a 64-degree wedge-shaped area at ranges from 500 to 1,600 nautical miles
A nautical mile is a unit of length used in air, marine, and space navigation, and for the definition of territorial waters. Historically, it was defined as the meridian arc length corresponding to one minute ( of a degree) of latitude. Today t ...
(925 to 3,000 km). ROTHR was originally intended to monitor ship and aircraft movement over the Pacific, and thus allow coordinated fleet movements well in advance of an engagement. In 1991, a prototype ROTHR system was installed on the isolated Aleutian Island of Amchitka
Amchitka (; ale, Amchixtax̂; russian: Амчитка) is a volcanic, tectonically unstable and uninhabited
island in the Rat Islands group of the Aleutian Islands in southwest Alaska. It is part of the Alaska Maritime National Wildlife Refu ...
, Alaska, monitoring the eastern coast of Russia. It remained in use until 1993, and 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 trade
The illegal drug trade or drug trafficking is a global black market dedicated to the cultivation, manufacture, distribution and sale of prohibited drugs. Most jurisdictions prohibit trade, except under license, of many types of drugs through ...
, covering Central America
Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...
and the Caribbean
The Caribbean (, ) ( es, El Caribe; french: la Caraïbe; ht, Karayib; nl, De Caraïben) is a region of the Americas that consists of the Caribbean Sea, its islands (some surrounded by the Caribbean Sea and some bordering both the Caribbean Se ...
. 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 (, ; ), officially the Republic of Colombia, is a country in South America with insular regions in North America—near Nicaragua's Caribbean coast—as well as in the Pacific Ocean. The Colombian mainland is bordered by the Car ...
. It also operates in the anti-drug trafficking role. The third, and final, production system was installed in Puerto Rico, extending anti-drug surveillance past the equator, deep into South America.
Soviet Union/Russia
Beginning as early as the 1950s, the Soviet Union had also studied OTH systems. The first experimental model appears to be the Veyer (Hand Fan), which was built in 1949. The next serious Soviet project was Duga, built outside Mykolaiv
Mykolaiv ( uk, Миколаїв, ) is a List of cities in Ukraine, city and List of hromadas of Ukraine, municipality in Southern Ukraine, the Administrative centre, administrative center of the Mykolaiv Oblast. Mykolaiv city, which provides U ...
on the Black Sea
The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Roma ...
coast near Odessa
Odesa (also spelled Odessa) is the third most populous city and municipality in Ukraine and a major seaport and transport hub located in the south-west of the country, on the northwestern shore of the Black Sea. The city is also the administrativ ...
. Aimed eastward, Duga first ran 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 (, also , ; rus, Но́вая Земля́, p=ˈnovəjə zʲɪmˈlʲa, ) is an archipelago in northern Russia. It is situated in the Arctic Ocean, in the extreme northeast of Europe, with Cape Flissingsky, on the northern island, ...
.
This was followed by the first operational system Duga-1
''Duga'' (, ) was an over-the-horizon radar (OTH) system used in the Soviet Union as part of its early-warning radar network for missile defense. It operated from July 1976 to December 1989. Two operational ''duga'' radars were deployed, wit ...
, known in the west as Steel Yard
''Duga'' (, ) was an over-the-horizon radar (OTH) system used in the Soviet Union as part of its early-warning radar network for missile defense. It operated from July 1976 to December 1989. Two operational ''duga'' radars were deployed, wit ...
, which first broadcast in 1976. Built outside Gomel, near Chernobyl
Chernobyl ( , ; russian: Чернобыль, ) or Chornobyl ( uk, Чорнобиль, ) is a partially abandoned city in the Chernobyl Exclusion Zone, situated in the Vyshhorod Raion of northern Kyiv Oblast, Ukraine. Chernobyl is about no ...
, it was aimed northward and covered the continental United States. Its loud and repetitive pulses in the middle of the shortwave radio bands led to its being known as the "Russian Woodpecker" by amateur radio
Amateur radio, also known as ham radio, is the use of the radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency communic ...
(ham) operators. The Soviet Union 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 near Komsomolsk-on-Amur
Komsomolsk-on-Amur ( rus, Комсомольск-на-Амуре, r=Komsomolsk-na-Amure, p=kəmsɐˈmolʲsk nɐɐˈmurʲə) is a types of inhabited localities in Russia, city in Khabarovsk Krai, Russia, located on the west bank of the Amur Rive ...
in the Russian Far East, also covering the continental United States and Alaska.
In early 2014, Russia announced a new system, called Container
A container is any receptacle or enclosure for holding a product used in storage, packaging, and transportation, including shipping.
Things kept inside of a container are protected on several sides by being inside of its structure. The term ...
, that was to see over 3000 km.
Podsolnukh (Sunflower) - Coast-horizon shortwave station short-range radar. Designed to detect surface and air targets at a distance of 450 km. Designed for use in coastal surface and air control systems within the 200-mile economic zone. "Sunflower" allows operators to automatically and simultaneously detect, track and classify up to 300 offshore and 100 air objects beyond the radio horizon, and provide their coordinates to the targeting systems and armaments of ships and air defense systems. The radar passed state tests in 2008. Currently, three stations are on duty, in the Sea of Okhotsk, the Sea of Japan, and the Caspian Sea.
Australia
A more recent addition is the Jindalee Operational Radar Network
The Jindalee Operational Radar Network (JORN) is an over-the-horizon radar (OHR) network that can monitor air and sea movements across . It has a normal operating range of to . It is used in the defence of Australia, and can also monitor mari ...
developed by the Australian Department of Defence Department of Defence or Department of Defense may refer to:
Current departments of defence
* Department of Defence (Australia)
* Department of National Defence (Canada)
* Department of Defence (Ireland)
* Department of National Defense (Philipp ...
in 1998 and completed in 2000. It is operated by No. 1 Radar Surveillance Unit of the Royal Australian Air Force
"Through Adversity to the Stars"
, colours =
, colours_label =
, march =
, mascot =
, anniversaries = RAAF Anniversary Commemoration ...
. Jindalee is a 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 of systems based on these individual radar geometries is the added requirement f ...
(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 , but in 1997 the prototype was able to detect missile launches by China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
over distant.
Jindalee uses 560 kW compared to the United States' OTH-B's 1 MW, yet offers far better range than the U.S. 1980s system, due to the considerably improved electronics and signal processing.
Canada
Canada has been investigating the use of High Frequency Surface Wave Radar (HFSWR) for surveillance of the 200 nautical mile Exclusive Economic Zone (EEZ) for more than 30 years. Research was initiated in 1984 with the re-purposing of a decommissioned LORAN-A navigation beacon for undertaking experimentation in aircraft, vessel and iceberg tracking. Research continued for the next decade and in 1999, Canada’s installed two SWR503 HFSWR systems at Cape Race and Cape Bonavista, Newfoundland. The sites underwent a technology evaluation in 2000 and were subsequently upgraded and operationally evaluated in 2002.
The following is a quote from the October 2002 Operational Evaluation (OPEVAL) performed by Canadian Department of National Defence:
"HFSWR is a beneficial addition to the Recognized Maritime Picture (RMP). Of all the data sources evaluated, it was the only sensor offering near real-time information updates. It provided frequent reporting and generally demonstrated reliable tracking of surface targets in its area of coverage. When the HFSWR system was combined with other data sources, there was a synergistic effect that improved the overall quality of the RMP. Furthermore, from the analysis of the potential contribution to the surveillance-related Force Planning Scenarios, it was evident that the RMP would benefit from the addition of the HFSWR as a new data source."
International sales of the SWR503 radar followed with operational systems installed in Asia (2008) and Europe (2009).
In 2007 operation of the Canadian systems was halted due to concerns over the potential for harmful interference with primary spectrum users. In 2010 the unique capability of HFSWR to provide low cost surveillance of the EEZ resulted in a re-evaluation of the technology and subsequent development of a 3rd Generation, (3rd Gen) HFSWR system based on the principle of sense-and-adapt technology that enabled operation on a non-allocated, non-interference basis through the use of Dynamic Spectrum Management . Additional developments included improved range performance, better positional accuracy and reduction of false tracks and earlier track initiation.
In June 2019, MAEROSPACE was granted a global license to design,, manufacture, and internationally market the Canadian HFSWR System and its derivatives.
France
The French
French (french: français(e), link=no) may refer to:
* Something of, from, or related to France
** French language, which originated in France, and its various dialects and accents
** French people, a nation and ethnic group identified with Franc ...
developed an OTH radar called NOSTRADAMUS during the 1990s (NOSTRADAMUS stands for New Transhorizon Decametric System Applying Studio Methods (French: ''nouveau système transhorizon décamétrique appliquant les méthodes utilisées en studio'').) In March 1999, the OTH radar NOSTRADAMUS was said to have detected two Northrop B2 Spirit flying to Kosovo. It entered service for the French army in 2005, and is still in development. It is based on a star-shaped antenna field, used for emission and reception (monostatic), and can detect aircraft at a range of more than 3,000 kilometers, in a 360-degree arc. The frequency range used is from 6 to 30 MHz.
Launched officially in 2009, the Frenc
STRADIVARIUS research project
developed a new over-the-horizon radar (High Frequency Surface Wave Radar – HFSWR) capable of monitoring maritime traffic up to 200 nautical miles offshore. A demonstration site is operational since January 2015 on the French Mediterranean coast to showcase the 24/7 capabilities of the system that is now offered for sale by DIGINEXT.
China
A number of OTH-B and OTH-SW radars are reportedly in operation in China. However, transmission from these radars causes much interference to other international licensed users.
One set of Chinese OTH-B radars is found on Google Maps for th
transmitter
an
receiver
Iran
Iran is working on an OTH radar called Sepehr, with a reported range of 3,000 kilometres. It is currently operational.
Brazil
The OTH 0100 Radar is capable of monitoring vessels beyond 200 MN (370 KM) away from shore, exceeding the direct line of sight of conventional radars.
India
India has developed a variety of long and short range radars. Although it doesn't have an operational over the horizon radar at present, India's Swordfish Long Range Tracking Radar
Swordfish is an Indian active electronically scanned array (AESA) long-range tracking radar specifically developed to counter ballistic missile threat. It will be a part of the Indian Ballistic Missile Defense Programme. First testing of this ...
, a part of India's missile defense system has a maximum range of 800 kilometers currently being upgraded for 1500 kilometers.
DRDO
The Defence Research and Development Organisation (DRDO) (IAST: ''Raksā Anūsandhān Evam Vikās Sangaṭhan'') is the premier agency under the Department of Defence Research and Development in Ministry of Defence of the Government of India, ...
's LRDE
Electronics and Radar Development Establishment (LRDE) is a laboratory of the Defence Research & Development Organisation (DRDO), India. Located in C.V. Raman Nagar, Bengaluru, Karnataka, its primary function is research and development of rad ...
is working on a prototype OTH radar. The design work of system is already complete and a prototype OTH is expected to realised by late 2021. The prototype will have two different types of arrays and itself will determine best frequency to use to track objects. After successful trials of existing system, India is expected to develop a large OTH radar based on same design.
Alternative OTH approaches
Another common application of over-horizon radar uses surface waves, also known as groundwaves. Groundwaves provide the method of propagation for medium-wave AM broadcasting below 1.6 MHz and other transmissions at lower frequencies. Groundwave propagation gives a rapidly decaying signal at increasing distances over ground and many such broadcast stations have limited range. However, seawater, with its high conductivity, supports groundwaves to distances of or more. This type of radar, surface-wave OTH, is used for surveillance, and operates most commonly between 4 and 20 MHz. Lower frequencies enjoy better propagation but poorer radar reflection from small targets, so there is usually an optimum frequency that depends on the type of target.
A different approach to over-the-horizon radar is to use creeping 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 bod ...
s or electromagnetic surface waves at much lower frequencies. Creeping waves are the scattering into the rear of an object due to diffraction
Diffraction is defined as the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a s ...
, 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, although processing the returned signal is 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
The Sea of Japan is the marginal sea between the Japanese archipelago, Sakhalin, the Korean Peninsula, and the mainland of the Russian Far East. The Japanese archipelago separates the sea from the Pacific Ocean. Like the Mediterranean Sea, it h ...
. A newer system has recently been used for coastal surveillance in Canada, and is now offered for sales by Maerospace, Australia has also deployed a High Frequency Surface Wave Radar.[ Senator Robert Hill, ]
Landmark Land Use Agreement For High Frequency Surface Radar
'', Ministerial Press Release 33/2004 from the Australian Department of Defence, 25 February 2004
Notes
References
;Citations
;Bibliography
*Peter Laurie
"An eye on the enemy over the horizon"
''New Scientist'', 7 November 1974, pp. 420–423.
*Nathaniel Frissell and Lyndell Hockersmith
"Seeing Beyond: Over the Horizon Radar Systems and HF Propagation"
Virginia Tech, 2 December 2008
External links
{{Commons category, Over-the-horizon radar
Radar Systems on Shortwave
an extensive list of OTH and similar radar systems compiled by Wolf Hadel, August 2013
A Canadian Perspective on High-Frequency Over-the-Horizon Radar
nbsp;— paper by R. J. Riddolls, Defence R&D Canada, Ottawa
The Development of Over-the-Horizon Radar in Australia
nbsp;— paper by D.H. Sinnott on the Australian Department of Defence Web site
Google maps link
nbsp;— Russian "Steel-Yard" radar near Chernobyl
Chernobyl ( , ; russian: Чернобыль, ) or Chornobyl ( uk, Чорнобиль, ) is a partially abandoned city in the Chernobyl Exclusion Zone, situated in the Vyshhorod Raion of northern Kyiv Oblast, Ukraine. Chernobyl is about no ...
.
Radar
Ground radars