Sea Technology

JUN 2015

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

Issue link: http://sea-technology.epubxp.com/i/527607

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Navigation

Page 25 of 76

www.sea-technology.com June 2015 / st 25 U nderwater navigation is essential for a diverse range of applications, such as subsea surveying, safe opera- tion and recovery of UUVs, swimmer delivery systems, and naval mine hunting and neutralization. The increasing use of UUVs throughout the past decade has seen signifcant advances made in the range of available sensors and sub- systems. Advanced payloads have been the main focus for overall development as operators look to expand the capa- bilities of vehicles and to undertake missions that were not previously considered safe, effective or economical. This has led to new and innovative payloads being developed, which are constantly being reduced in size and weight while offer- ing greater capability and value. This is especially true for acoustic sensors. Although GPS and other radio signals have been widely used for surface vessel navigation, these technologies are ineffective for underwater navigation, because electromag- netic waves are blocked by seawater. Inertial sensing is a suitable and widely used technology for autonomous under- water navigation. However, the position error tends to drift in the absence of input from an aiding sensor. The most success- ful combination for underwater navigation has therefore been to combine inertial technol- ogy with velocity measurement from an acoustic sensor that measures speed from echoes re- fected from the seafoor. Acoustic velocity sensing is a dual-use technology with many commercial applications, in addition to military ones, such as mine countermeasures. As UUVs become an integral component of a modern naval force, spending on payloads for intelligence, surveillance and reconnaissance (ISR) missions continues to be signifcant. In addition, the use of sensor tech- nology has seen a greater focus on imaging, navigation and communication for payloads capable of relaying real-time and relevant information to other units. Leading-edge re- search and development for the military market has in turn led to a greater emphasis on the civilian use of UUVs, with applications including surveillance, imaging, detection and mapping for commercial sectors, such as offshore energy as well as ocean science and marine archaeology. Commercial applications include offshore and deep offshore geophysical survey and construction support as oil is being discovered and extracted in deeper water beyond the continental shelf. Doppler Velocity Log The majority of in-service acoustic velocity logs exploit the Doppler principle, which is the frequency shift of the seabed or seawater echoes due to the relative motion of the sonar. A typical Doppler velocity log (DVL) consists of four narrow beams steered in the fore/aft and port/starboard di- rections to estimate the 3D velocity vector from Doppler shifts associated with each beam. The beams are steered Next-Generation Acoustic Velocity Sensors for Underwater Navigation CVL Array Lessens Cost, Complexity by Streamlining Receiver Redundancy By Dr. Jeremy Dillon The AquaTrak correlation velocity log produced by Kraken Sonar Systems Inc. of Canada.

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