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Harbours keeping harm at bay.

So far airports have been favourite spots for terrorist action, with infrastructures as main targets or as a point-of-entry for subsequent attacks inside airliners However, one has to remember that sea traffic really is the backbone of world commerce. Harbours are not only commercial terminals for world trade, but may also become the main point of entry when a military mission starts in a theatre of operation that has a direct access to sea or that is close to a neighbouring country with such access.

Since the Twin Towers attack, 'defence against terrorism' has become a major priority of the Nato Conference of National Armaments Directors, and the Naval Group 3 responsible for mines and mine countermca-sures within the Nato Naval Armaments Group, has subsequently become responsible for harbour protection.

Initially that responsibility was given to Italy, which maintained it from 2004 to 2010 when the responsibility was passed on to Portugal. Among the Alliance the scientific leadership in that field is provided by the Nato Underwater Research Centre (Nurc), based at La Spezia, Italy (see box).

By a large margin the most difficult threat to deal with comes from below the waves. Nowadays re-breather systems are available commercially and scuba diving courses for amateurs that want to try something different from conventional air compressed air bottles are common in many countries. This development thus provides a good starting point for any terrorist planning on exploiting the shelter of water depths to approaching a target--just as flying schools and simulators did allow al-Qaeda to train its suicide pilots for the 'nine-eleven' attacks.

Underwater sensors must thus be able to pick the weakest signals in normally noisy maritime harbour scenario and discriminate a diver from other underwater objects to minimise false alarm rates. In the mid-1990s high frequency multi-beam sonars were identified as the most promising assets to develop swimmer detection systems. In spite of their high cost, such active sonars are available to provide some reasonably long range detection, although research in passive sonars segment might soon provide efficient alternatives.

Against divers the optimal active sonar frequency has been found to lie somewhere between 85 and 100 kHz. The other parameters that have a strong influence on the detection range are obviously target reflective strength and background noise, not to mention the deployment geometry.


A key player in the active sonar diver detection field is Reson from Denmark, with subsidiaries in Britain, Germany, the Netherlands, Singapore and the United States. The company developed stationary, mobile and portable detection systems and is currently focusing on two of its products of the Seabat family of sonars, the 7128 and the 7112. The Seabat 7128 is a high-resolution forward-looking sonar that covers a 128[degrees] sector and can work on two different frequencies, 200 and 400 kHz. They can be equipped with different types of transmitter arrays, particularly the TC2179, which is optimised for shallow waters.

Used at 200 kHz it has a typical range of 500 metres with a range resolution of 25 mm and provides high-resolution images of intruders to allow rapid classification. It can be easily mounted on surface and underwater platforms of small dimensions and is mostly designed as a portable or mobile system.

The Seabat 7112 works at a lower frequency, 100 kHz, and provides 360[degrees] coverage with a typical range of about 1000 metres and a 37.5-mm range resolution. It can be installed on the seabed using specially designed tripods and optical fibre cables to connect the sensor to the shore base station. Recent testing showed the possibility of linking systems via wireless connections, as well as operating the two sonars from the same console, which is an important amenity for integrating the capabilities of the two systems, in other words, the greater range of the 7112 and the better resolution of the 7128.The latter can, for example, be mounted on a harbour patrol boat and sent into the target area, from where it can operate in the shorterrange mode (about 300 metres) at 400 kHz to positively identify the threat.

Sonardyne in Britain has, for its part, developed the Sentinel Intruder Detection Sonar. It uses cots processing units, but its key features are a state-of-the-art sonar head on the one hand and the automated detection, classification and tracking software on the other.

The sonar comes in the form of a cylindrical-shaped object with a 330-mm diameter and a 432-mm height. The centre frequency is 70 kHz, with a 20-kHz bandwidth. The 256 beams with a three dB azimuthal receiving beamwidth of 3.5[degrees] allow for a 360[degrees] surveillance pattern while the receive and transmit vertical beamwidth is eleven degrees. In addition, the sonar head incorporates an attitude and heading reference unit to allow motion compensation when the Sentinel is used from a suspended cable or from a moving platform. It weighs 35 kg, but immersed this is reduced to six kg, which allows it to be used on many robotic unmanned vehicles.

The typical detection range announced bv Sonardyne is 400 metres on a ten-meter-deep sand bottom (or 600 metres at a 20-metre depth), while a mud bottom at a depth of ten metres depth will offer a range of 900 metres. The maximum operating depth for the Sentinel is 50 metres. The link between the sonar head and the processor unit, based on two high-performance personal computers, is ten km via fibre optic cable.

Each control station can handle up to ten sensor units, but according to the company user list the maximum number of Sentinel sonars operating in a single location is five. The sonar is in service in the US Navy and Army, one European navy and was tested and evaluated by the Royal Navy.

In early 2011 Sonardyne teamed with Flir and won a multi-million dollar contract in the United Arab Emirates for the installation of a coastal infrastructure security system.The project leader is Flir, which will provide ground surveillance radars and CCD imagers for above-water surveillance, while Sonardyne will ensure underwater protection with its Sentinel The entire system will be seamlessly integrated via the Flir command and control software platform.

According to Flir, this type of expandable layout is the first of its kind and is expected to have entered full operational capability by the time these lines are read, i Other such turnkey systems have been acquired by Kuwait and Saudi Arabia.

From Canada this time, Kongsberg Mesotech proposes a series of active sonars. Its DDS 9000 diver detection system is also a multi-beam unit, but with a titanium head that connects directly to a surface interface unit. Its 256 beams with a beam width of 1.5[degrees] can determine very small targets, namely divers at ranges in excess of 600 metres.

The DDS 9000 has a coverage of 200[degrees] and supports multiple types of pulses such as CW (Continuous Wave) and FM Chirp (Compressed High Intensity Radar Pulse). Telemetry configurations include a standard Ethernet connection or an optional optical fibre configuration, the latter allowing communication over 500 metres of cable without the need for external hardware. For ranges of up to 5000 metres an external AC to DC power converter must be installed within 500 metres of the sonar head.

The sonar head is connected to the interface unit via a single power and telemetry cable. The interface is then linked to the sonar processor. A connection to a local area network is available and can be used to connect the system to the Kongsberg Defender II Tactical Processor or to a C2/C4ISR command and control system.

The DDS 9001 has similar features but is mostly devoted to mobile applications, as it has a built-in motion compensation system and provides a 360[degrees] coverage. Its maximum detection range is stated at 800 metres, which may indicate that the diver detection range is slightly lower. The DDS 9001 weighs about 114 kg and can be linked to the Defender II Tactical Processor. Depending on application--waterside or shipborne--two different sets of software are used.

Kongsberg Mesotech systems are currently used to protect the port of Long Beach and are also in use with two different European navies. In August 2008 Kongsberg signed a contract with Asel-san of Turkey for the delivery of two integrated underwater surveillance systems aimed at protecting two of the Turkish Navy main bases, those of Aksaz and Foca. According to the terms of the contract, which had a value of [euro]16.4 million, the systems should be delivered in August 2011 to Aselsan, which acts as the prime contractor for the overall base surveillance and detection system.

Kongsberg Defence & Aerospace proposes the C-Scope network-based surveillance and protection system. Two main sensors are available. The first is the Lasar 10--an active/passive long-range detection sonar that is made of a configurable transmitter array operating in the two to 20-kHz band, one amplifier unit includes a linear eight-channel amplifier, one to eight receiver arrays and one to eight data acquisition units converting analogue hydrophone signals to digital data frames.The arrays and the transmitter can be deployed in different layouts which can be optimised according to environmental conditions.

The second is the Lasar 40 active/passive system based on a network of arrays, the transmitter operating in the 30 to 45-kHz band with a horizontal beam pattern of 180[degrees], 270[degrees] or 360[degrees] for seabed mounting and jetty wall mounting, a vertical beam width of 3[degrees] to 10[degrees] and vertical beam steering of [+ or -] 10[degrees]. The receiver has a sector coverage of 180[degrees] or 360[degrees], a range resolution of 0.1 metres, a bearing resolution of 1.8[degrees], while accuracy is 0.18[degrees] in bearing and less than 0.01 metres in range.

For monitoring harbour approaches Kongsberg also offers its Pasar passive sonar, with a typical 100-metre-long array with a diameter of only 72 mm containing 334 hydrophones that can pick signals in a frequency range between 10 and 2500 Hz. To exploit synergies between its sonars Kongsberg offers the DDS Processor, a complete active acoustic system sonar processing, detection, tracking and classification, fusion and display unit that since late 2010 is based on the new Defender III processor.

The autonomous detection tracking and classification software distinguishes divers from marine life while target data can be exported to central command and control systems. Its operating system software uses a Linux-based operating system.The system comes in a transport case that contains the laptop, the processor unit, an Ethernet link at 10/100/1000 Mbps. for a weight of less than 15 kg without the case itself.

Atlas Elektronik UK took over the Cerberus swimmer detection sonar family from Qinetiq.The first member of the family, the Cerberus Mod 1, was developed in mid-2000 and came in the form of a large sensor (1.4 metres in height and a 0.7 metres in diameter) offering a 1600-metre detection range, a coverage between 30 and 360[degrees], a 1.9[degrees] azimuth resolution and a 0.03-metre range resolution.

'These performances have in tact been improved by the much smaller Cerberus Mod 2, which has an 1800-metre detection range but is a truly man-portable system as all components--sensor, cable and operator workstation--weigh less than 25 kg. The sonar sensor is 0.4 metres high. has a 0.3-metre diameter and weighs 23 kg. The system ensures detection and tracking of an open-circuit diver respectively at 900 and 850 metres, and 700 and 675 for closed-circuit divers.

The system covers 360[degrees] with an azimuth bearing resolution of less than 1[degrees] and a range resolution of 25 mm, can operate at depths between five and 50 metres, and can be deployed on the seabed, from piers and jetties or from a ship. The software provides automatic detection, classification and tracking: an alert message appears on the display, while track data such as position, classification (open or closed circuit), speed, heading etc. are provided to the operator in a window showing target tracking in zoom mode.

Saab markets two diver detection systems, the DD90 and the portable PDD360, as well as a virtual fence. The DD90 is a static system that can work as a stand-alone or integrated into a C2 suite. It has a range of 300 metres with a 90[degrees] coverage, but can be complemented by the PDD360 which ensures a 360[degrees] sur-veiilance. Operating at 120 kHz, it has a range of 300 metres, a bearing accuracy of 1[degrees] and a range accuracy of ten per cent of the sensor range. Both systems feature a multi-target tracker with autonomous detection, classification and monitoring of divers and small submersibles.

The Virtual fence is a passive system that detects underwater and surface vessels. It is made of magnetic, acoustic and pressure sensors with a 50-metre separation deployed on a 3000-metre long cable. These multiple detecting systems allow good discrimination capability between artificial and biological phenomena.

Westminster International offers its WG Mids (Marine Intruder Detection Sonar), a single- or multi-head active sonar system designed to automatically detect and track underwater and surface threats, principally divers (scuba or closed-circuit, with or without propulsion aids), surface swimmers and robotic underwater vehicles. The Mids can detect and track multiple targets up to a range of 900 metres on mud bottom at a ten-metre depth, classification of divers-like targets taking place at 450 metres. Detection ranges on sand bottom at ten and 20 metres are respectively of 400 and 600 metres.

The system is based on a sonar head operating at 70 [+ or -] 20 kHz generating 256 beams with azimuthal and vertical receiver beam-widths respectively of 3.5[degrees] and 11 [degrees].The sensor head weighs 35 kg in air, is 432 mm tall and has a diameter of 330 mm, its maximum operational depth is 50 metres. It can be located up to 100 metres from the processor using a copper cable or up to 30 km using optical fibre.The sensor head can be deployed on a tripod on the seabed, along jetties, as well as on surface ships either freely suspended, pole mounted or on through-hull mounts.

The system can operate in a standalone mode with a single head or can be networked, each command station being capable to accept up to ten sensors, each head requires a sonar processor.

Dsit of Israel developed an innovative, cost-effective diver detection sonar system known as the Aqua Shield which, based on a 120[degrees] array and using one, two or three arrays, provides 120[degrees], 240[degrees] and 360[degrees] coverage according to needs. A single 360[degrees] emitting source working at 60 kHz is used, with continuous wave and low-frequency modulation modes.

Two configurations are available, one with above-water electronics for pier installation and one with underwater electronics for seabed installation. Standard detection ranges declared by the manufac turer are 1500 metres for a swimmer deliv ery vehicle, 1000 metres for a diver with open circuit apparatus and 700 metres with closed circuit apparatus, range accuracy being estimated at less than 0.5 metres while bearing accuracy is 0.1[degrees].

The system sensor array can withstand the explosion of 0.2 kg of TNT at five metres. The Aqua Shield command and display unit, to which multiple sensors can be linked, provides automatic target recognition and tracking as well as automatic target classification; the system can handle up to 1000 targets simultaneously.

The Centrum Techniki Morskiej of Gdynia, Poland, developed its DDS Diver Detection Sonar based on a wide-band, multi-element transceiver developed by Materials Systems in the United States. It operates at frequencies between 60 and 80 kHz, has a maximum depth of 100 metres and provides a coverage of 180[degrees] x 15[degrees]. Capable of simultaneously handling up to ten targets, the DDS' declared ranges are 250 metres for surface objects and 700 metres for divers.

The Polish company also produces a Monostatic Acoustic Barrier, operating at 60 kHz with a 20-kHz bandwidth, its sensors covering a 13.5[degrees] x 13.5[degrees] sector with a detection range of 600 metres, and a Magnetic Linear Barrier able to protect a length of between 80 and 2000 metres. Both systems are passive, as opposed to the previously described sonars that are all active.

Active Sonar Issues

Active sonars have numerous drawbacks, ranging from a relatively high rate of false alarms, (although this problem is being addressed by sophisticated algorithms) to easy detection by the enemy and hazard posed to marine life--the hearing sensitivity of marine mammals ranges from 0.01 to 200 kHz according to a US Coast Guard paper.

Numerous research centres are working on passive acoustic systems to detect underwater threats.The New Jersey-based Stevens Institute of Technology established a research laboratory environment in support of the US Navy in the area of anti-terrorism and force protection. The outcome of the institute's work is the Spades (for Stevens Passive Acoustic Detection System), which allows the passive acoustic detection, tracking and classification of numerous surface and underwater sources of sound such as surface vessels, swimmers, various types of divers and unmanned underwater vehicles.

The system is based on four hydrophones sensitive up to 100 kHz and providing simultaneous acquisition and analysis of acoustic signals, which determines the target's bearing relative to the system central mooring that houses the electronic components required for signal conditioning, data acquisition, preprocessing, storage and transmission.The hydrophones can be located up to 50 metres from the mooring point. An underwater cable connects the mooring to a land-based computer.

The system has shown good potential, although the current man-machine interface is still research-oriented. In the Netherlands the TNO laboratory is linked to the Stevens Institute and is currently developing the Sobek, which is based on passive sonar installed in sensor buoys that act together as nodes in a underwater detection network to secure the required waterside areas. The Dutch Ministry of Defence has expressed interest in the Sobek and has funded an experimental trial in the navy port in Den Helder in October 2010.

USVs and UUVs

Robotic surface and underwater systems are part of the harbour protection scenario; although currently they are mostly being tested in various roles, there is still some way to go before such systems will be allowed to move autonomously in a military base, not to say in a public harbour. Several surface vessels are available on the market and are described in a separate article in this issue (see page 40).

Command and Control

Most integration companies provide C4I suites that carry out data fusion from all the harbour protection sensors, including those relevant to the ground security of the facility, in order to optimise detection, identification and tracking phases, providing the operators with the best possible effector for countering the threat according to the ROEs. In January 2011, Atlas Elektronik and Cassidian announced the foundation of Signalis, which regroups all the activities of Sofrelog and Atlas Maritime Security, mostly devoted to maritime surveillance but that can also be involved in port protection.

In Italy, Selex Sistemi Integrati recent ly carried out Harpex, a Harbour Protection Exercise that lasted 48 hours, during which navy personnel manned the Archimede system. About one attack per hour was envisaged, therefore the system was manned by a four-men crew on three shifts, the sensors were three radars, two electro-optic systems and one diver detection sonar, the only effector being an acoustic system. UGVs have already been integrated into the system, which is the culmination of a long series of tests and developments carried out in the last few years in co-operation with the Italian Navy.

RELATED ARTICLE: The Role of the Nurc

s part of the Atlantic Alliance scientific organisation, the Nurc is the centre of excellence for analysing and researching methods and systems for the protection of commercial and military harbours. The Nato approach evolved around mid-2000 through a series of tests and trials. According to Dr. Ronald T. Kessel, Project Manager Port Protection at the La Spezia-based centre, one of the key developments was that of the open sea simulator that contributes to developing a gaming architecture for complex exercises. This system can input numerous simulated threats, such as divers, helicopters and fast boats, as well as simulated or real sensors and effectors.

The task of the Nurc is to deliver solutions to Nato Allied Command Transformation, to which the centre is subordinated. Getting the clearance for using active sonars into harbours is a key problem, thus passive sonars are used.

However, ports are typically noisy environments, therefore robust analysis tools are needed to extract the breathing repetition signature from the clutter. Once identified, an active sonar can be actuated to track a diver, therefore a combination of the two systems looks like a promising option, and experiments are underway combining monostatic active sonars and passive systems. Robotic boats, used as forward eyes to acquire information on possible surface intruders, can be used to challenge small boats by crossing their path or even by ramming them, they can launch entanglement devices to stop them, and can even hunt divers using active sonar. However all these functions are still to be integrated. As for underwater systems their main role seems to be that of floor inspection chasing underwater explosives using sonar imagery.
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Title Annotation:Harbour protection
Author:Valpolini, Paolo
Publication:Armada International
Date:Aug 1, 2011
Previous Article:Common (ground) sense.
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