Supported by Sonardyne International Ltd’s Scout USBL acoustic positioning technology, ARA Incorporated has recently completed a subsurface survey of Terminal 91 in the Port of Seattle. Commissioned following the discovery of World War II munitions on the seafloor under the cruise ship facility at Pier 91 within the terminal, ARA’s operation was to identify and clear any magnetic anomalies that could potentially warrant further investigation.
A complete vessel based acoustic positioning system, Scout USBL is designed for tracking divers, ROVs and towfish in waters up to 1,000 metres. Calculating the position of a subsea target by measuring its range and bearing from a vessel mounted transceiver to an acoustic transponder fitted to the target, the system offers high accuracy performance with efficient subsea tracking operations. To undertake the survey, ARA mobilised its Remotely Operated Vehicle (ROV) ROUMRS which was fitted with a Sonardyne WSM 6 transponder and a Scout transceiver was deployed from the side of the dock on a simple pole arrangement. Positioning data from Scout was fed to the accompanying Sonardyne ViewPoint navigation software which transforms the coordinates of surface vessels, subsea vehicles and structures into geographical information that is overlaid on easy-to-use guidance displays.
John Coughlin, Director of Engineering and Sciences at ARA commented: “The results of our subsea survey were fantastic and we were particularly impressed with the sub-metre accuracy we achieved in this challenging environment. It wouldn’t have been possible without the help of the team at Sonardyne in Houston. Not only did they provide the best equipment for the job but their invaluable expertise, integrated software and on-site training meant that our objectives were fulfilled in a timely and cost-effective manner.”
Ralph Gall, Technical Sales Manager at Sonardyne in Houston remarked, “Although commonly used by the offshore survey and ocean scientific industries, Scout is equally at home tracking a diver or target in just a few metres of water so we were confident that it was the right solution for ARA to use on this unusual project.”
Subsea World News Staff , July 20, 2012; Image: Sonradyne