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Connecting the Underwater Battlespace

For close to 100 years, the submarine has been a potent force in the armoury of Naval Forces around the world. The ability to 'lose' a German Wolf Pack in the North Atlantic was a factor that almost cost Britain her maritime lifeline - and stiff lessons regarding detection and ASW counter-measures were learned. The Battle of the Atlantic may have utilised the first true military Command and Control to prosecute this immense and cunning threat. Today this has evolved to become Command, Control, Communications, Computers, Intelligence, Surveillance and Reconnaissance (C4ISR). C4ISR is packed with technology but cannot succeed without effective, timely Communications...

Multiplying the Effectiveness of Helicopter ASW Sensors

The introduction of low frequency active dipping sonar systems has enabled ASW helicopters to achieve significantly increased detection range. As a result a single helicopter, rather than a pair of helicopters, is adequate for both search and attack operations. However, modern threats comprising small diesel submarines operating in littoral waters, in adverse acoustic conditions, remain a challenge. This paper shows how recent developments in sonobuoys combined with a low frequency active dipping sonar system can have a force multiplier effect, providing significantly improved performance as well as improving the helicopter's tactical freedom. The paper quantifies performance improvements, based on simulation, for a specific combination of dipping sonar and expendable active sources and passive receivers, for an illustrative barrier scenario...

Modular Projector System
(Winner : Best Paper, UDTE 2006)

Over the past several years, UEMS has developed the Modular Projector System (MPS), an invention by Bruce Armstrong. MPS exploits acoustic interaction between closely-spaced underwater sound projectors to produce a compact low-frequency broadband source that is straightforward to reconfigure for specific resonance frequency, bandwidth, and source level by simply repositioning the basic building blocks from which it is composed. Previous papers on MPS described the concept and it's extraordinary flexibility in configuration and performance, and compared modeled results for different configurations using the MAVART finite element software. This paper compares modeled and measured frequency responses of a two MPS prototypes comprising flexural disc transducer stacks in several configurations, validating the modeling and performance predictions. Planned future modeling enhancements include moving from axisymmetric to fully three-dimensional models of non-collinear arrays and our roadmap towards this goal is described. Interpretation of the physical test results offers new insight into this remarkably versatile transducer...

An Overview of ASW Sonobuoy Types and Trends

A new generation of ASW sonobuoy types, with modular all-digital architectures, provide improved performance, and enable exciting new modes of operation. This paper provides an overview of Ultra's current ASW sonobuoy types, in terms of operating characteristics, in-buoy processing, aircraft interfaces, and performance. The characteristics of each buoy type are discussed in relation to various operational applications, including passive search and localisation, monostatic active localisation, and multistatic search and localisation...

Recoverable Tethered Optical Fibre (RTOF) Submarine Communications

For submarines to be included in Network enabled operations, military commanders must be able to communicate effectively with their underwater assets. This must be done without compromising the primary attribute of the submarine; stealth. Furthermore, connectivity should not be at the expense of platform manoeuvrability nor should it unduly compromise or delay mission objectives. Current towed antenna systems provide relatively low data rate communication links and submarine masts present moving surface targets that are identifiable by radar. The Recoverable Tethered Optical Fibre (RTOF) system, under development by Ultra Electronics with our partners Weir Strachan & Henshaw, provides UHF SATCOM connectivity to underwater platforms extending the Network enabled capability to the deep. This is achieved at speed and depth while maintaining covertness. RTOF technology provides new and enhanced capabilities for joint operations both in the littoral and the deep. An overview of the system is presented and the design principles are described...

Use of Adaptive Antenna Calibration for Sonobuoy Location on the NH90 ASW Helicopter

A novel geolocating system has been developed and integrated into the NH90 helicopter by Galileo Avionica and Ultra Electronics. This enables the helo to track a drifting field of sonobuoys without having to overfly the buoys, thereby retaining tactical freedom to manoeuvre. RF angle-of-arrival (AOA) measurements, from a lightweight antenna array, are used to estimate buoy positions. The tracking algorithm has been optimised by mathematical simulation, based on measurements from a prototype aircraft. System performance depends on the AOA error characteristics, and on accurate synchronisation of AOA measurements with navigation data. An innovative feature of the design is that the large and unpredictable AOA measurement errors are adaptively calibrated by exploiting the buoys as pseudo-reference points. Navigation data and measurement timing synchronisation has been given particular attention during the system integration activity. This paper describes the operating principles of the system, and some of the lessons learned during its development and integration. It will be of particular interest to the airborne ASW community, but the adaptive calibration technique may also have wider application...

Surface Ship Torpedo Defence (SSTD)

The new SSTD system entering service with the United Kingdom's Royal Navy in 2004 provides torpedo defence across a wide variety of surface ship classes, both warship and support vessels. This paper details Ultra's SSTD system in terms of its transferable 'stand-alone' compact design, minimal ship-fit impact and ease of operation by operators with a broad spectrum of skill levels. This novel system includes the use of a flexible towed countermeasure to reduce operator workload during array streaming and recovery evolutions...

Submarine Sonar Calibration and Organic Signature Ranging

The paper describes two systems developed by Ultra, each launched from a submarine's underwater signal ejector (SSE).

The Calibrated Active Disposable Sound Source (CADISS) system enables a submarine to calibrate and check its own sonars by deploying a sonobuoy that transmits a set of tones with very accurately controlled frequencies and source levels.

The deployment of a calibrated source to check the sensors on a submarine usually involves a surface consort vessel deploying acoustic sources and a suitably remote location. The CADISS System means that a submarine can check and calibrate its own sensors as and when required and without the involvement of other vessels.

The Organic Signature Range (OSR) system enables a submarine to determine its own acoustic signature using a SSE launched sonobuoy store and inboard processing equipment.

Currently submarines need to travel to a fixed acoustic range for monitoring their acoustic signature. The OSR enables a submarine to deploy a sonobuoy that receives the boat's signature and transmits the information back to the submarine for recording and analysis on an inboard processor. The OSR system enables a submarine to monitor its own signature when required and when conditions are suitable.

Both systems use a common inboard processing system and the paper will show examples of outputs and the deployment sequence.