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High Frequency Surface Wave Radars (HFSWR) for Ship detection and tracking far beyond the horizon

In recent years organized crime in maritime regions has flourished, threatening both secure flow of goods from Exclusive Economic Zones (EEZ)  and lives of participants in the marine operations. Security threats and humanitarian risks caused by trafficking (drugs, weapons, etc.), irregular transport of migrants, maritime terrorism or even piracy are on the increase and are forcing nations to strengthen the surveillance and security of their environment. maritime, in particular within their Exclusive Economic Zone. Controlling these risks has become a strategic issue for many countries, and more broadly for the European Union, which seeks to implement solutions allowing early warning signs of a threat to be detected as early as possible. of a risk.

The granting of coastal nations’ sovereign rights over their 200 nautical miles (nm), Exclusive Economic Zone (EEZ) established the requirement for persistent surveillance.  Moreover, in some areas of the world, the situation is so serious that UN  and/or EU intervention has been required, since nations which have jurisdiction over those waters have limited resources.  Since EEZs are huge bodies of water which can cover hundreds of thousands of square kilometers, complete monitoring is much easier said than done.

 

One way to achieve complete EEZ monitoring, especially if your primary targets are non-cooperative vessels. First approach utilizes optical and microwave sensors on platforms such as satellites and airplanes, thus avoiding sensor’s limitations, but introducing platform’s limitations. The most limiting factor is interrupted data availability, since no airplane is able to stay in the air constantly during whole year and all-weather conditions, while satellites are orbiting around Earth and will be over the zone of interest for a limited time.

 

Other approach uses network of HFSWRs  to ensure constant surveillance well beyond horizon. The signals of Conventional microwave radars propagate in a straight line and cannot detect objects beyond their line of sight.  The maximum range of these radars is limited by the radio horizon – slightly far away than the optical horizon. OTH radars use very long wave lengths with special properties of propagation.

Image result for High Frequency Surface Wave Radar (HFSWR)

The high-frequency surface wave radar (HFSWR), also known as the HF surface over-the-horizon radar, operates in the 3–30 MHz frequency band at wavelengths between 100 m and 10 m, respectively.  The HFSWR can provide additional information on maritime traffic because it can detect targets over the horizon, has continuous temporal coverage, and can estimate vessel velocity based on Doppler data.

Persistent Surveillance Coverage of Maritime Surveillance Areas

The illustration above shows the use of High Frequency Surface Wave Radar used for monitoring the EEZ, and coastal microwave radar for monitoring territorial waters. These systems are augmented by the self reporting automatic identification system (AIS). Coastal microwave radars, augmented with Raytheon’s Marine Small Target Tracker (MSTT) can be strategically located to provide line-of-sight, high resolution surveillance within territorial waters.

 

As illustrated below, microwave radars are limited to surveillance within the horizon. Detection ranges can be increased by elevating the radar antenna. For persistent surveillance of vessels throughout the EEZ Raytheon has developed a land based, long-range, High Frequency Surface Wave Radar (HFSWR). These radars operate in the HF portion of the RF spectrum (where the lower the frequency of operation the greater the detection range).

 

Compared with conventional instruments such as buoys, anemometers, and microwave radars, HFSWR can be employed to an all-weather and all-time surveillance far beyond the visible horizon.   Since the price of HFSWR network is significantly less than the combined cost of aforementioned sensors and data are available constantly during whole year, it is clear why these radars are slowly becoming the sensors of choice for maritime surveillance at over-the-horizon (OTH) distances.

 

 

High frequency surface wave radar (HFSWR) systems

High frequency surface wave radar (HFSWR) systems,  that operate from coastal installations, so that the radar energy can couple into the salt water.  HFSWR refers to a classification of radar that utilizes the surface-wave mode of propagation and thatoperate in the 3 MHz to 30 MHz frequency range; surface waves have the following characteristics:(a) they attenuate directly as functions of distance (range), frequency and surface roughness;(b) they propagate efficiently in vertical polarization only; and(c) they require a conducting surface, such as a saline ocean, to propagate.

 

High Frequency Surface Wave Radar (HFSWR) takes advantage of the diffraction of electromagnetic waves over the conducting ocean surface.  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.

 

High-frequency surface-wave radar (HFSWR) has been widely applied to early warning for decades, including the detection of airborne targets and surface targets. In addition to early warning uses, HFSWR provides a unique ocean surface dynamics parameters remote-sensing capability based on the Doppler spectrum characteristics of the sea echo backscattered from the 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 detection range is dependent on many factors. The range obtainable is dependent on the frequency of operation, radiated power and vessel size as well as the prevailing environmental conditions. The radar signal will experience a greater rate of attenuationas the radar frequency is increased or, for a given frequency, the sea state increases.

 

Image result for High frequency surface wave radar (HFSWR) systems

HFSWRs that are used for long-range vessel tracking typically operate in a pulse-Doppler mode, where the radar emits a coherent pulse train. Vessels, which are within the area illuminated by the radar, reflect thesepulses back to the radar, where the echoes are received by a linear array of antennas. The signal receivedon each antenna is digitally processed to enhance the signal-to-interference ratio, where the term interferenceincludes all unwanted signals such as sea clutter, external noise, ionospheric reflection as well as interference fromother users of the band. The returned echoes are processed and sorted according to range, velocity (Doppler)and bearing. The echoes are then compared against a detection threshold chosen to achieve a predeterminedconstant-false-alarm-rate (CFAR). If the magnitude of an echo exceeds the threshold it is declared a detection.These detections are then forwarded to a tracking algorithm that associates consecutive detections in to tracks

 

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.

 

HFSWR can be classified into onshore and shipborne cases based on the platform where it is employed. Besides the advantages of onshore HFSWR, shipborne case has the agility and maneuverability, which can not only enhance the survivability in complex ocean environment but also enlarge the detection distance on open sea. Thus, ocean remote sensing with shipborne HFSWR is expected to receive increasing attentions.

Bistatic System

Currently, most HFSWR systems operate in a monostatic mode that requires the collocation of the transmitter and the receiver. This raises practical issues in terms of the coastal space required for installation of both the transmitting and the receiving antenna arrays, as well as the problem of mutual interference between antennas. These issues can be overcome by resorting to a bistatic radar system in which the transmitter and the receiver are located some distance apart.

 

In a bistatic HFSWR system, the receiver has robust anti-active directional jamming and anti-destruction characteristics because of the physical separation of the transmitter and the receiver, giving it unique advantages and potential regarding anti-electronic interference. A shipborne HFSWR system has the advantage of flexibility and it can increase the radar detection range beyond that of an onshore HFSWR. A system in which one of the transmitting or receiving stations is installed on the coast and the other is placed on a ship forms a coast–ship bistatic HFSWR system. Such systems can be classified either as a coast-transmit ship-receive (CTSR) bistatic HFSWR or as a ship-transmit coast-receive (STCR) bistatic HFSWR depending on whether the receiving station is placed on the ship or the coast, respectively.

 

A CTSR bistatic HFSWR has the advantages of anti-stealth, anti–interference, and no onboard electromagnetic radiation because the ship carrying the receiver can move to areas far from the coast. Compared with STCR systems, CTSR systems can exploit fully the flexibility of a shipborne platform and further expand the radar detection range by adjusting the attitude of the shipborne platform and changing the radar system configuration, e.g., adjusting the radar spindle angle. However, the azimuth resolution of such systems is reduced because shipboard platforms are limited by the size of the platform and thus the radar receiving station aperture is typically limited to ≤100 m.

 

In an STCR bistatic HFSWR system, the shipborne equipment comprises only the transmitter, and there is no need to consider the deployment of a receiver, signal processor, or other equipment. In addition, the antenna aperture of the radar system is not limited by the size of the ship, which means that a large aperture-receiving antenna array could be installed onshore to improve azimuthal resolution. However, the fixed nature of the coast-based receiving station means that the receiving array spindle angle cannot be changed, which limits the detection range of the radar system to a certain extent.

 

In addition, a transmitter/receiver–receiver radar system could be formed by adding a second coast-based/shipborne transmitter–receiver monostatic radar on the same basis as the coast–ship bistatic radar. Then, the detection performance and positioning accuracy of the marine target could be improved through fusion of the results of the two systems.

 

Russian Podsolnukh (Sunflower) radar

Podsolnukh coastal OTH radars. Podsolnukh is surface-wave radar capable of detecting naval targets up to 300km away and air targets up to 450km away, as long as they fly over the water. They too are an important part of the country’s defense capabilities.

 

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.

 

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.

Image result for he Podsolnukh E is a coast-horizon shortwave short-range radar system

“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.”

Image result for Podsolnukh (Sunflower) radars

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.

 

“In the fall of 2014, the over-the-horizon radar detected various targets and sent their coordinates to the Grad Sviyazhsk and Uglich corvettes. In January, the Podsolnukh detected four low-flying Su-24 bombers. The data was forwarded to the Dagestan frigate, whose ballistic missile defense system successfully locked onto targets,” the newspaper detailed. Over-the-horizon stations have a major advantage when compared to other radars. They are capable of detecting stealth objects. For the Podsolnukh, the F-22 and the F-35, the best fighter jets in the US arsenal that could fly deep behind enemy lines, are no different from aircraft that do not use stealth technology.

 

Then at the February 2009 IDEX show in Abu Dhabi a Russian source confirmed to Fisher the sale to China of the 300km range Podsolnukh-E surface-wave OTH radar. Russia’s Black Sea Fleet will be reinforced by the deployment in Crimea of the Podsolnukh short-range over-the-horizon surface-wave radar with 450 km target acquisition capacity, a source in the Russian Defense Ministry told TASS on 17 December 2014. “The sea-based Podsolnukh radar will be deployed in Crimea that will be ‘looking’ to the Bosporus,” the source said.

 

Russia will station additional Podsolnukh (Sunflower) radars that are capable of detecting cutting-edge stealth aircraft, including Lockheed Martin’s F-35 Lightning II and F-22 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.

 

Canada’s HFSWR

Canada has been investigating the use of HFSWR for persistent surveillance of the EEZ for more than 20 years. Early development cumulated in 2003 with the deployment of two SWR-503 HFSWR systems for monitoring the economically significant Grand Banks region on Canada’s east coast. Raytheon Canada Limited (RCL) subsequently sold a number of SWR503 systems to international customers;
however, operation of the Canadian systems was terminated in 2007 due to concerns related to the potential for the systems to cause interference to HF communication users. The international systems continue to remain in operation.

 

The requirement for providing persistent surveillance of the EEZ remained, and in 2010 Defence Research and Development Canada (DRDC) completed a comprehensive study of applicable technologies. The study concluded that HFSWR remained the most viable sensor for persistent surveillance based on a combination of cost and performance. At the same time, RCL started the development of their next
generation HFSWR to address obsolescence issues associated with the SWR503 design.

Primary design requirements included being a modular and scalable architecture, having the ability to support wideband operation, and to be compatible with other users of the HF spectrum. This latter requirement led to the development of a conceptually new power amplifier design that resulted in a constrained bandwidth and ultra-low spectral side-lobes. The new generation radar also included an enhanced spectrum management system and reduced real estate requirements all at a low-cost. This last requirement resulted in additional requirements to maximize commercial-off-the-shelf (COTS) equipment and digital technology, and maximum reuse of SWR-503 software. The system was specified as a minimum to match the SWR-503 performance.

 

Independently and in parallel, the DRDC team developed its system requirements for a new generation HFSWR that would meet
Industry Canada’s stringent requirements for operating on a non-interference mode with HF communication users while remaining available
24/7. Other enhancements were also sought. In 2011 Raytheon Canada was awarded the contract to design and build a third generation
HFSWR system for Persistent Active Surveillance of the EEZ (PASE). This third generation HFSWR system would be installed and demonstrated at a site located near Halifax, Nova Scotia.

 

Canada’s Third-Generation High Frequency Surface Wave Radar (HFSWR)

Canada’s third-generation HFSWR forms the foundation of a maritime domain awareness system that provides enforcement agencies with real-time persistent surveillance out to and beyond the 200 nautical mile exclusive economic zone (EEZ).

 

The Third generation HFSWR system is a mono-static pulse Doppler radar. The third generation radar incorporates an ultra linear HF power amplifier specifically designed, by RCL, for pulsed Doppler radar operation. The HF power amplifier design results in very low spectral side-lobe levels and consequently minimal spectral leakage that otherwise would have resulted in adjacent channel interference.

 

Raytheon Canada and the Canadian military developed such radar, designated the HF-SWR-503. This is an oceanic surveillance system for monitoring such illegal activities as drug trafficking, smuggling, piracy, illicit fishing and illegal immigration. In addition, it may be used for tracking icebergs, environmental protection, resource protection, sovereignty monitoring and remote sensing of ocean surface currents and winds as well as assist in search and rescue operations.

 

It consisted of an array of monopoles 660 meters (2,165 feet) long, with the monopoles spaced at about 50 meters (164 feet), corresponding to half the wavelength of the radar’s 3 MHz operating band. The array has a field of view of 120 degrees and can track targets to the limit of Canada’s 370 kilometer (200 nautical miles) oceanic economic exclusion zone. It can obtain positions accurate to within hundreds of meters. Raytheon stated that a similar array could be used to track low-flying cruise missiles if it operated at a frequency of 15 to 20 MHz.

 

Canada’s third-generation HFSWR system has been developed by Raytheon Canada in collaboration with Defence Research and Development Canada, based on a cognitive sense-and-adapt architecture . Cognition, utilizes intelligent signal processing, which builds on learning through interactions of the radar with the surrounding environment, as well as feedback from the receiver to the transmitter, which is one of the facilitators of intelligence. The objective was to utilize knowledge obtained either by sensing the local environment or from trusted third-party sources to maximize the probability of track initiation, whilst minimizing the probability of false or otherwise erroneous tracks.

 

The primary objective of the cognitive system is to detect and track targets via the effective allocation of radar resources, with a secondary objective to confirm the identification of known targets. For example, if a target is being observed by other means or is known to be of low-value for the mission, then resources can be diverted to higher-priority targets. Alternatively, data related to weather conditions, or other environmental data such as wind speed and direction or ambient temperature data, can be used to aid the optimization of the radar. It can be noted that the cognitive cycle is similar in context to the standard OODA decision cycle: observe, orient, decide, and act.

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Canada’s third-generation cognitive HFSWR system consisting of an adaptive HFSWR (Act), the ingestion and processing of data into the optimizer (Sense), the determination of the optimum radar processing for the mission (Learn) and the application of optimized processing parameters (Decide).

 

A second enabling feature of the radar is that it operates in a slow-time multiple-input multiple-output (MIMO) mode. During operation, the radar sends coded pulses on an alternating basis through the two separate transmitting antennas strategically located at either end of the receiver array. On receiving, the pulses returned from both antennas are separated to form a virtual array that has an equivalent performance to a physical aperture of twice the length.

 

Radar is used to track and classify vessels but cannot provide positive identification. For this type of identification, other systems
must be utilized. For example, the requirement for vessels to self-report using the Long Range Identification and Tracking (LRIT) system was established in 2006 by the International Maritime Organization (IMO).

 

Another source of identification is the Automated Identification System (AIS). AIS is an IMO mandated short range, VHF anticollision system that broadcasts, among other things, non-encrypted host vessel identification and location. Range is limited by design to
approximately line-of-sight. Interception of AIS signals using a satellite based receiver allows worldwide coverage throughout the
EEZ and international waters.

 

A German OTH-SW application with more civil use is the WERA radar. The WERA system is a shore based remote sensing system to monitor ocean surface currents, waves and wind direction. It uses the principle of FMCW with very slow sweep period of typically 0.3 sec. This oceanography radar can pick up back-scattered signals (Bragg effect) from ranges of up to 200 km.

 

Diginext presents the Stardivarius transhorizon radar

DIGINEXT, in partnership with the company Antheop, has been carrying out research work on these issues for many years and has developed a new generation radar, Stradivarius, using surface waves in the HF band to monitor maritime traffic in- beyond the radio horizon. While current radars have a range of a few tens of kilometers, Stradivarius can detect small-scale boats (25 m) up to 200 nautical miles (approximately 370 km) from the coast.

 

Complementing the existing maritime surveillance systems (maritime patrol, satellite surveillance, etc.), Stradivarius is capable of ensuring permanent surveillance (24/7) in real time and in sea conditions up to Sea 5. A the first operational copy of this radar is already installed in the Mediterranean. The Stradivarius radar, a real technological breakthrough The unparalleled performance of Stradivarius as well as its low environmental footprint, allowing an extremely discreet integration into the coastal framework, convinced the European Commission, which retained this technology within the framework of the RANGER project in the “maritime border security” theme of the program. European Horizon 2020.

 

This project, which notably associates the French Maritime Affairs Department and the Greek and Italian navies, will enable experiments to be carried out in the Mediterranean. “The Stradivarius radar is a real technological breakthrough. The RANGER project will allow us to further improve this French technology, in an international operational context, and to continue to develop the state of the art. It will also allow us to demonstrate the performance and benefits of our technology in terms of cost and efficiency for the long-distance detection of possible threats or support for rescue missions. », Specifies Thomas FOURQUET, Director of DIGINEXT.

 

 

 

 

 

References and Resources also include:

https://www.globalsecurity.org/wmd/world/russia/podsolnukh.htm

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5539545/

 

 

 

About Rajesh Uppal

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