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Over-The-Horizon radars being integrated into air defence networks to detect and track stealth Aircrafts and Aircraft carriers

Conventional microwave radars such as those commonly seen at airports propagate in a straight line and cannot detect objects beyond their line of sight i.e. beyond the visual horizon. Over The Horizon Radar (OTHR) utilises the Ionosphere to reflect the radiated signal ‘over the line of sight horizon’. Such radars can detect stealth aircrafts and ships from extremely long detection ranges from 700 to 4000 and also being employed for border protection, disaster relief and search and rescue operations.

OTHR and HFSWR radars have become important element of air  defence networks of many countries including China, Australia, Iran, US and Russia.  They  have the capability to defeat the stealth of aircrafts like the Northrop Grumman B-2 Spirit, F-35 or F-22 by detecting and tracking them from hundreds of kilometers.

China has reportedly set up a high-tech radar system in Inner Mongolia with a detection range of up to 3,000 kilometers, a move to spy on South Korean and Japanese military maneuvers, according to Chinese media. The installation comes amid a spat with South Korea on the deployment of a Terminal High-Altitude Area Defense (THAAD) battery from the US. THAAD is a missile defense system Beijing and Russia fear could be a tool to be used to spy its military activities. OTH radars could also detect stealth aircraft and locate inter-continental ballistic missiles and other types of missiles fired by other countries. The radar could allegedly confirm the target of an enemy within a minute after launching and could issue an early warning three minutes later.

This is the second OTH radar installed by China. Its first OTH is set up in the Hubei-Henan-Anhui triangle. All two radars are used to monitor the entire western Pacific if used together with spy satellites.

Russia plans to step up its fourth Sunflower (Podsolnukh-E) radar system, which, according to Russian experts, is capable to detect US stealth aircraft, such as В-2 Spirit, flying over the ocean at a height of 500 kilometers, the China Topix informational website reported. As the website reported, citing sources in the Russian Defense Ministry, the new Sunflower will be stationed in the Novaya Zemlya archipelago in the Arctic Circle. China Topix noted that the archipelago notorious as a place of the most large-scale tests of nuclear weapons. So, in the days of the former Soviet Union, 224 nuclear explosions had been implemented there before 1990. According to the media, Russia intends to build six over the horizon radar systems in the Arctic. Russia has been carrying out rapid Arctic militarization by building New airbases, icebreakers, ground forces, missiles and and carrying out military exercises there.

Over The Horizon Radar (OTHR)

There are two types of OTH radars: The first is the Skywave OTHR that utilises the refractive properties of the ionosphere to refract or bend transmitted HF electromagnetic waves back to Earth. When these refracted HF waves hit a radar reflective (metal) surface of sufficient size — either airborne or maritime — some of the energy is reflected back along the transmission path to the OTHR receiver. Sophisticated computer systems then process the received energy to discern objects within the radar’s footprint.   Skywave OTHR that are able to  detect aircraft and ships at very long ranges (between 500 km and 3000 km – ignoring any double bounces).

These radars are typically capable of estimating the 2-dimensional coordinates of targets; namely, latitude, longitude, speed and heading. They can perform simultaneous tracking of separate targets.  Such radars offer extremely long detection ranges (from 700 to 4000 km) but also very low resolution (from some hundreds of meters up to 20 km).

Other type of OTH radars are Surface wave radar systems, in particular high frequency surface wave radar (HFSWR) systems,  that operate from coastal installations, so that the radar energy can couple into the salt water.  High Frequency Surface Wave Radar (HFSWR) takes advantage of the diffraction of electromagnetic waves over the conducting ocean surface. The transmitted signal follows the curved ocean surface, and a system can detect aircraft, and ships, beyond the visible horizon,  at ranges out to roughly 300 km. HFSWR exploits a phenomenon known as a Norton wave propagation whereby a vertically polarised electromagnetic signal propagates efficiently as a surface wave along a conducting surface.

The successful detection of a target by a surface wave radar system traditionally involves compromises between a number of factors, including propagation losses, target radar cross-section, ambient noise, man-made interference, and signal-related clutter. In detecting a target at roughly 150 kilometers using HFSWR large error tolerances are experienced in both range (.+.1 to 2 km) and azimuth (.+.1. degree.) due to limited band width availability and physical antenna size constraints.

Some of the OTH radars are JORN of Australia, ROTH of Ratheon USA, NOSTRA-DAMUS of ONERA, France and STEEL YARD of NIIDAR, Russia. All of them operate from approximately 5-30 MHz. The most powerful radar is Steel yard of Russia which transmits 1500 KW.

OTH Radars being low frequency band radars possess anti-stealth capabilities, offering considerable capabilities of detecting targets such as stealth planes. Stealth techniques such as shaping have been designed with the aim to reflect most of the radar energy away from an expected radar antenna and not back to it. However, techniques such as shaping and coating with Radar-Absorbent Materials (RAM) is most effective in microwave frequencies mainly in the X and Ku bands, and is less effective at Longer wavelengths such as VHF or High frequency (HF) radars such as OTHR. When the wavelength of the incident electromagnetic (EM) wave is comparable to the physical dimension of the object, it results in enhancement of RCS and in large amplitude oscillations in the RCS. This is due to the resonance effect between the direct reflection from the target and scattered waves which “creep” around it.

How does it work?

OTHR systems operate on the Doppler principle, where an object can be detected if its motion toward or away from the radar is different from the movement of its surroundings. OTHRs are typically made up of very large fixed transmitter and receiver antennas (called ‘arrays’). The location and orientation of these arrays determines the lateral limits or arc of radar’s coverage. The extent of OTHR coverage in range within this arc is variable and principally dependent on the state of the ionosphere.

OTHRs do not continually ‘sweep’ an area like conventional radars but rather ‘dwell’ by focusing the radar’s energy on a particular area – referred to as a ‘tile’ – within the total area of coverage. The transmitted HF energy can be electronically steered to illuminate other ‘tiles’ within the OTHR’s coverage as required to satisfy operational tasking or in response to intelligence cuing.

Under certain atmospheric conditions, only specific radio frequencies will get reflected back towards the ground. The “correct” frequency to use depends on the current conditions of the atmosphere. So systems using ionospheric reflection need real-time monitoring of the reception of backscattered signals to continuously adjust the frequency of the transmitted signal.

Australia’s Jindalee Operational Radar Network

The Jindalee Operational Radar Network (JORN) is an over-the-horizon radar (OTHR) network that can monitor air and sea movements across 37,000 km2. It has a normal operating range of 1,000 km to 3,000 km. It is used in the defence of Australia, and can also monitor maritime operations, wave heights and wind directions.

The JORN defence system is a network of three remote over-the-horizon radars in Queensland, Western Australia and the Northern Territory. These radars are dispersed across Australia — at Longreach in Queensland, Laverton in Western Australia and Alice Springs in the Northern Territory — to provide surveillance coverage of Australia’s northern approaches.  It provides wide-area surveillance to support the Australian Defence Force’s air and maritime operations, border surveillance, disaster relief, and search and rescue operations.

The JORN radars have an operating range of 1000–3000km, as measured from the radar array. Of note, the Alice Springs and Longreach radars cover an arc of 90 degrees each, whereas the Laverton OTHR coverage area extends through 180 degrees.

JORN does not operate on a 24 hour basis except during military contingencies. Defence’s peacetime use of JORN focuses on those objects that the system has been designed to detect, thus ensuring efficient use of resources.

Operation and uses

The JORN network is operated by No. 1 Radar Surveillance Unit RAAF (1RSU). Data from the JORN sites is fed to the JORN Coordination Centre at RAAF Base Edinburgh where it is passed on to other agencies and military units. Officially the system allows the Australian Defence Force to observe air and sea activity north of Australia to distances up to 4000 km.

This encompasses all of Java, Irian Jaya, Papua New Guinea and the Solomon Islands, and may include Singapore. However, in 1997, the prototype was able to detect missile launches by China over 5,500 kilometres (3,400 mi) away.

The “backscatter” signal is extremely small due to reflection losses. The very long wave length used by such low frequency radar make it very difficult to pick out the relatively small target presented by an aircraft against the very large target presented by the earth. It takes a huge amount of data processing to pick large targets out of earth clutter.

For an aircraft or maritime vessel to be detected, it must possess a radar reflective (metal) surface of sufficient size so that sufficient HF radar energy is reflected back along the transmission path to the JORN receiver.

“JORN is expected to detect air objects equivalent in size to a BAe Hawk-127 aircraft or larger and maritime objects equivalent in size and construction to an Armidale-class patrol boat or larger,” according to Australian Air force.


BAE Systems to bid for Australia’s JORN Phase 6 upgrade

BAE Systems is to compete for the major Phase 6 upgrade of the Australian Department of Defence’s (DoD) Jindalee Operational Radar Network (JORN). The upgrade to the over-the-horizon radar (OTHR) network is designed to ‘open’ the system’s architecture enabling the insertion of next generation technologies and extend the operational life of JORN to beyond 2042, the Phase 6 upgrade is expected to take place in 2018.

Russian Podsolnukh (Sunflower) radar

Russia will station additional Podsolnukh (Sunflower) radars that are capable of detecting cutting edge stealth aircraft, including Lockheed Martin’s F35 Lightning II and F22 Raptor, to protect the country’s exclusive economic zones in the extreme North, the Baltic Sea and Crimea in 2017, Rossiyskaya Gazeta reported 10 August 2016.


Russia’s Black Sea Fleet will be reinforced by the deployment in Crimea of the Podsolnukh short range over the horizon surfacewave radar with 450 km target acquisition capacity, a source in the Russian Defense Ministry told TASS on 17 December 2014. “The seabased Podsolnukh radar will be deployed in Crimea that will be ‘looking’ to the Bosporus,” the source said.

According to the article, the fourth radar system “can become operational in 10 days and needs a team of just three people to remain operational.” The systems must be placed at a distance of 370 kilometers from each other in order to ensure full coverage. Currently, Russia has three Podsolnukh-E radar systems, which are operating in the Sea of Okhotsk, in the Sea of Japan and in the Caspian Sea. However, these stationary systems can be easily detected due to its massive radar towers.

“The Podsolnukh E is a coast-horizon shortwave short-range radar system that is capable to detect both air and sea targets, approaching to it from the sea. It can simultaneously detect, track and classify 100 aerial targets and 300 maritime targets in an automatic mode,” the article reads. “A distinctive feature of the Podsulnukh is its mammoth antenna array up to five kilometers long and five meters tall that can identify aerial targets 500 kilometers away and sea targets up to 400 kilometers away.”

The system is able to determine their position and capable to transfer coordinates of a target to various weapon systems, such as fighter jets, vessels and antiaircraft missile batteries. The Sunflower can detect stealth aircraft, such as the American F-35 super-expensive modern multirole fighters, “as clearly as aircraft of the WWII era,” the author of the article writes, citing Russian sources.


Chinese OTH radars

China is reported to have developed its first OTH-B radar back in 1967; Since the 1980s two further installations have possibly been added to the inventory, with at least one system looking out into the China Sea area reportedly to target (US Navy) aircraft carriers.

Backscatter systems function at the upper end of the High Frequency (HF) band, typically between 12 and 28 MHz. OTH-B radars are bistatic systems, this is where the transmitter and receiver use different antennas at widely separated locations to achieve detection results.

China’s OTH-B is said to use Frequency Modulated Continuous Wave (FMCW) transmissions to enable Doppler measurements, the suppression of static objects and the display of moving targets.

In 2008 Asian military sources told Richard Fisher that China had placed a new long range OvertheHorizon (OTH) radar station in Hainan Island. Then at the February 2009 IDEX show in Abu Dhabi a Russian source confirmed to Fisher the sale to China of the 300km range PodsolnukhE surfacewave OTH radar.


China deploying Anti-Stealth OTH Radar in the South China Sea

In 2015 Victor Robert Lee of The Diplomat reported, “Fiery Cross Reef, Subi Reef and Mischief Reef are China’s largest military installations in the Spratlys, but they are still under construction and do not exhibit the more sophisticated defensive capabilities now present at China’s smaller bases on four other reefs in the Spratlys: Cuarteron, Gaven, Hughes, and Johnson South.”

“These facilities are being equipped with state-of-the-art sensor towers, weapons tracking and firing platforms and tracking/firing guidance radars, as well as an array of electronic sensors and satellite communications infrastructure. For example, a satellite image taken August 23 shows that Cuarteron has a new antenna farm that Rogers considers reminiscent of Australia’s Jindalee over-the-horizon radar network, which has a range of up to 3,000 kilometers.”

“China appears to be building an anti-stealth radar system on an artificial island in the middle of the South China Sea, where a military-grade system would be useful in detecting stealth aircraft in the contentious and contested area,” Kyle Mizokami reports in Popular Mechanics.


China’s Anti-ship ballistic missile system can target US aircraft carriers through OTH radar and satellites

A constellation of satellites and at least one over-the-horizon radar give its Anti-Ship Ballistic Missile (ASBM) system the capability to work out the position of U.S. aircraft carriers at sea, according to assessments published by researchers at the National Institute of Advanced Studies in Bangalore.

Land-based ballistic missiles, carrying manoeuvrable warheads with conventional munitions, could then, if needed, target the aircraft carriers at a distance of about 2,000 km.

Although the land-based ballistic missiles can target aircraft carriers using just the Yaogon constellation, the number of targeting opportunities become fewer if cloud cover obscures the view of satellites with optical sensors, observed Prof. Chandrashekar.

China’s constellation of Yaogan military satellites includes those for electronic intelligence (ELINT) gathering that detect radio signals and other electronic emissions from an aircraft carrier and its associated warships. China currently has three clusters of ELINT satellites that provide global surveillance.

By incorporating an over-the-horizon radar that can continually track aircraft carriers up to a distance of about 3,000 km, the Chinese gain the flexibility to launch the ballistic missiles whenever they choose, he pointed out.


Ghadir, Iran’s over-the-horizon radar

Ghadir, is an Iranian over the horizon radar Ghadir is a 360°, 3D-radar, with a ceiling of 300 km, and a maximum range of 1,100 km. Unlike other OTHR’s, Ghadir doesn’t use FMCW modulation. Instead, it uses a shaped pulsed system which makes the edges of the signal hard to define. Because of this, the bandwidth of this signal can vary greatly, ranging from around 60 kHz to splattering over 1MHz, depending on the power of the received signal for the user

A senior Iranian Army general  spoke about plans of  Islamic Republic plans to unveil a variety of over-the-horizon radar systems covering a distance of 3,000 kilometers. Brigadier General Farzad Esmaili, the commander of Iran’s Khatam al-Anbiya Air Defense Base, said that the radars can help the Khatam al-Anbiya Air Defense Base “detect and monitor aircraft flying beyond [Iran’s] borders.”


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