Sea Technology

MAY 2013

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

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In the case of legacy equipment designs, the adoption of technology that can improve performance can be impractical because of program requirements or other factors. This enhanced technology may not be required in all cases to allow for successful operation of this legacy equipment. For instance, in shallower-water environments less than 3,500 meters depth, the attenuation levels may be the same, but operational ranges are greatly reduced. Therefore, the loss of signal due to attenuation can have a much smaller effect on the acoustic communications system. Other environmental factors, such as multiple-path sound refection, or multipath, which is the refection of acoustic energy off features such as the seafoor, sea surface, geological structures or ships, can interfere with acoustic communications signals. Typically in shallower water environments, multipath is the major cause of acoustic interference, so using a transducer with a lower acoustic output can be desirable even if the equipment is capable of tolerating some amount of multipath due to software coding. With knowledge in hand, manufacturers assist users in the selection of the best technology for their needs. In some cases, the easier-to-build and lower-cost potted transducer is ideal, while in other cases the increased output of the oil-flled transducer is the better option. These two offerings allow both users and manufacturers the ability to adapt products to fall within constraints of program budgets and requirements. No single transducer offering is ideal for all customer applications or budgets. (Top) The mooring being deployed during testing offshore Hawaii (note the three acoustic releases and acoustic modems used for signal monitoring). (Bottom) The topside deck-unit transducers rigidly mounted to ensure similar orientation and depth when transmitting and receiving. ted transducers tend to have lower acoustic-output levels and lower receive sensitivity when compared to transducers mounting the ceramic element in an oil-flled boot. Hydroacoustic attenuation, or the absorption and dispersal of acoustic energy as sound waves travel through the water, is very prominent in deepwater environments. For this case, deepwater environments are defned as seafoor depths of 3,500 meters or more. Given this attenuation, the operation of some acoustic systems can be challenging in these deepwater environments because of the loss of acoustic energy. This is acoustic energy that these high-technology systems require to process data, commands and operation requests. In these deepwater environments, the oil-flled transducer and its higher output capability, and increased receive sensitivity, are advantageous. 32 st / May 2013 Testing in Controlled Setting To provide empirical evidence as well as engineering analysis for users, Teledyne Benthos (Falmouth, Massachusetts) embarked on a focused test and evaluation program. The capabilities of each transducer were evaluated in the controlled environment of an acoustic test tank in March 2011 at Teledyne Benthos's facility in North Falmouth. Electronics systems were tuned to the different requirements and capabilities of the transducers, and a series of tests were performed. In this controlled setting, the potted transducer was able to achieve 188 decibels of maximum output power at 11 kilohertz when driven with a 20-watt transmitter, while the oil-flled transducer produced 193 decibels at 11 kilohertz, again with a 20-watt transmitter. Across the range of 7 to 15 kilohertz, increases ranging from 3 to as much as 9 decibels of increased power were observed, still using the same 20watt transmitter. Hawaii Testing The numbers observed in a controlled setting are useful, but, in the end, real-world performance is what counts. To prove the ability for acoustic systems to perform, a deepwater test was conducted in the waters surrounding the Big Island of Hawaii in September 2011. This location is ideal for testing because of the relatively short transit time to deep water. Approximately one hour from shore, the water depth www.sea-technology.com

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