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The increasing underwater threat represented by mines and Waterborne Improvised Explosive Devices (WBIED) together with unidentified intrusions into national waters, terroristic and adversary special forces attacks, together with the vulnerability not only of ports and approaching sea line of communications, but also of other coastal infrastructures as well as offshore facilities to these threats, have driving the development of layered and deployable alert and defence systems capable to be quickly put into place and requiring a reduced manned and logistic footprint. These include Diver Detection Sonars (DDS) and wider underwater detection systems together with rapid environmental assessment systems carried by underwater and surface, unmanned and manned platforms in order to, as quickly as possible, detect and identify the threats in the difficult environmental conditions of ports and shallow coastal waters. High frequency active sonar have become the answer to diver detection, classification, identification and tracking, together with underwater loudhailer to inform the diver is being tracked and to surface. In parallel to the increasing number of micro, small and medium UAVs and ROVs, together with unmanned surface platforms being put into service for conducting Rapid Environmental Assessment (REA), Mine Countermeasures (MCM), Intelligence, Surveillance and Reconnaissance (ISR) alongside hydro- and oceanographic operations, the industry has been developing payloads with increasing-capable but at the same time not-power hungry sensors able to be fitted to these small platforms.

Intruder Detection Systems

The Israeli DSIT Solutions company offers a complete range of around the clock, critical coastal sites and naval assets protection solutions, in service with a range of mostly undisclosed military, homeland security, oil and gas and other civilian customers. AQUASHIELD DDS offers a unique modular, open architecture and windows-based design with intuitive human-machine interface (HMI), operating at ‘a 60 KHz central frequency’ and offering a long range detection with up to 3,000 meters diameter coverage. Capable to handle more than 1,000 targets simultaneously, AQUASHIELD is indicated to have a detection range of 1,000, 700 and 1,500 metres respectively against open and closed circuit breathing apparatus-equipped divers and SDVs, alongside UUVs. The POINTSHIELD is the smaller and portable system of the same DSIT DDS family for protection of vessels at anchor and ships at berth, as well as being suitable for the fixed installations where limited area needs to be covered. Being easy to be deployed and retrieved manually or with mechanical systems, capable of fully automatic operations, it incorporates advanced signal processing allowing the detection of respectively open and closed circuit breathing apparatus-equipped at 500 and 700 m, alongside UUVs. DSIT also offers the SEASHIELD coastal surveillance system combining bottom-based active and passive sonar systems for long-range real-time underwater surveillance under a shore-based station.

Introduced in 2007 and sold to a wide range of customers including the US Navy and the US Coast Guard, Sonardyne has kept pace with users’ needs of the SENTINEL DDS, enhancing the system capabilities. Different variants are available, with the baseline version including Scylla underwater loudhailer, configured for most commercial and infrastructure protection, including support for networked sonar arrays and integration with third party C2 systems. The Sonardyne SENTINEL comes with two different sensor heads respectively suitable for expeditionary use with a lightweight aluminium housing (35 kg in the air/6 kg in the water) and for permanent installations with a super-duplex housing (45.5 kg in the air/18 kg in the water ). With a 70kHz centre frequency, the SENTINEL emits a 360° linear-period-modulated (LPM) pulse and uses 256 receive beams equally spaced along its perimeter to discriminate targets in up to 1500 m range even at high velocity. The results means SENTINEL can detect scuba divers up to 1,000 m range and divers with closed circuit breathing equipment up to 700 m, alongside UUVs and SDVs. The SENTINEL baseline suite includes one sensor head which can be mounter either way up or cable suspended, the sonar processor unit and the command workstation with intuitive HMI.

In Europe, Atlas Elektronik UK (AEUK) is offering the CERBERUS Mod2 DDS which found service with reportedly a dozen of customers, including German Navy, which was the first NATO customer to fit with a DDS one of its class of vessels (F125 frigates). The system, which is powered with ships cabling, can operate as a stand-alone system, without integration into the combat system. In the case of the German Navy, the components were required to meet additional requirements and standards, including a completely new design and build of a bespoke power supply and processing unit (PSPU) qualified to customer rigorous standard. Designed to meet the demands of both portable and shipborne applications, the CERBERUS Mod2 features a sonar head of compact design (400×300 mm and 23kg in air), while the complete system including the deployment cable, power supply and processing unit (PSPU) and remote laptop, weights around 72 kg. Operating with a frequency range of 70 to 130 kHz, and equipped with an automatic detection, classification, identification and tracking system, providing reliable alerting of multiple underwater targets with minimal false alarms, the CERBERUS Mod2 has a detection and tracking range for open and closed circuit divers of respectively 900+/850+ and 700+/675+ meters.
Last January, the Norwegian Norbit group, announced that Norbit Subsea was awarded an order from an undisclosed international customer for delivery of several GUARDPOINT surveillance sonar systems. Managed by proprietary GUARDPOINT Tracking Software, the portable system with a sensor head of <50 kg weight (in addition to <10 kg as topside unit), operating at 70 kHz frequency, has a maximum detection range against open circuit diver, closed circuit diver, SDV and midgets of respectively 800, 400 and 1,000 meters. Norbit Subsea also offers the Wide Band Multibeam System (WBMS) Forward Looking Sonar (FLS) for swallow water conditions and easy deployment.

In addition to other systems on the market, including the Spanish SAES’ DDS-03 portable high-frequency system characterized by high-performance even in difficult scenarios with unfavourable propagation conditions such as warm waters, and the Armelsan ARAS-2023, which is indicated as the first Turkish-made DDS, operating at 70 kHz frequency, with a 40 kg sensor head capable of detecting open circuit and close circuit divers, together with SDV respectively at 800, 400 and 1,000 m maximum range, to be embarked on the new Turkish Navy LHD, the Norwegian Kongsberg group, with its long experience with its DDS 9000 and vessels sonar families, is marketing the SD9500 system. The Kongsberg over-the-side dipping sonar offers diver detection, ASW and volumetric survey capabilities in shallow, reverberation-limited waters with a compact and lightweight design capable to be deployed by any vessel, including smaller vessels (10+ m) or Unmanned Surface Vessels (USVs). Finnish DA-Group is however proposing a lightweight modular and deployable underwater surveillance system with bottom-based sensors centred on the TURSO Target Detection System (TDS) developed by the same company for new sea mines applications.

Imaging Underwater Sensors

Among the latest technologies and solutions in the sensors segment which could make the difference, according to their developers and claimed capabilities to be operationally proven, the US company Klein Marine Systems (as part of MIND Technology company) has introduced its new generation AUV-MAKO integrated sonar payload for micro, small and medium AUVs and ROVs, alongside the MA-X View 600 for surface platforms, while the Canadian Kraken Robotics company is proposing its AquaPix MINSAS Commercial-off-the-Shelf (COTS) Synthetic Aperture Sonar (SAS) for integration into AUVs as well as surface towed solutions, such as the company’s KATFISH system.

The new Klein AUV-MAKO is a multiple sensors’ dry low-power payload, consisting of a shared processing engine and a set of focused 600 kHz side scan arrays and a μMA-X nadir imaging nose array in the first iteration of a pre-planned additional capabilities roadmap. The AUV-MAKO side scan delivers focused 600 kHz imagery at an optimum range of 50 meters per side with capability of reaching 120 meters per side. It produces 900 kHz-type resolution imagery without the range and motion limitations typical of an higher frequency system. The AUV-MAKO μMA-X system is based on Klein’s latest MA-X technology which provides imaging of the nadir gap directly under the path of the vehicle, with the same interpretive characteristics of the side scan sonars. The AUV-MAKO provides a true full-swath coverage with a >40% increase in survey efficient (extended mission duration or shorter time to cover the same area vs not-equipped with nadir AUVs), high contrast across the entire swath and in-stride multi-aspect view, alongside real-time integration with ATR systems thanks to on-board processing. In 2020, the μMA-X solution was delivered in support of US Navy Next Generation Small-Class UUV evaluation sponsored by the US Defense Innovation Unit (DIU) organisation. The same technology is applied to the Klein’s MA-X VIEW 600 towed body of 1.42m length and 24.7kg weight, incorporating company’s broadband CHIRP sides scan sonar and MA-X gap-filler, which already saw international success. The system allows 40 per cent less survey time at sea, 40 per cent less fuel consumption and higher probability to complete the survey in a window of good weather, according to Klein.

After being contracted in 2020 by the Danish and Polish MoDs to provide the KATFISH towed Synthetic Aperture Sonar (SAS) vehicle and the SEASCOUT Autonomous Launch and Recovery System (ALARS) and intelligent Tentacle winch, together with SeeByte’s embedded ATR capability for MCM operations, the Canadian Kraken Robotics company announced in October 2021 to have been contracted by Canadian government for testing of Kraken’s KATFISH towed SAS system by the Royal Canadian Navy (RCN) on board a vessel of opportunity and the untethered Light Weight SAS system, deployed on an RCN’s REMUS 100 AUV. The contract scope is to evaluate the new systems in supporting the RCN in the passage lanes survey along the coasts and into designated ports, alongside hydrographic duties. Both mentioned systems are based on the company’s AquaPix MINSAS, which is an off-the-shelf configurable SAS capable of 2×2 cm ultra-high definition imaging, which according to the Canadian company, can replace high-end side-scan systems at an affordable price, while delivering significantly higher resolution, range, and area coverage rates (ACR). The increased range and resolution and associated higher ACR of SAS over traditional SAS systems can significantly expand, according to Kraken Robotics, the capabilities of the customer’s AUV systems for a variety of tasks for naval, scientific, and commercial applications. Last February an undisclosed South Korean customer has ordered the 1000-meter rated AquaPix MINSAS 60 sonar for use in a military application.