Sea Technology

FEB 2014

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

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62 st / February 2014 www.sea-technology.com The extent of their potential usefulness has yet to be de- termined as the mobile AUV/glider platforms to which they can be mounted could make them strong assets for remote monitoring activities. For that purpose, in 2014, within the PERSEUS EU project, CMRE will integrate the volumetric array in the Teledyne Webb glider. The AUV was bottom mounted on the frame and used on two different sea bottom types (sand and mud). The seabed refection coeffcients for both sites were estimated by divid- ing the downward beam intensity with the upward beam in- tensity obtained from conventional plane-wave beamform- ing. Sub-bottom profling was also computed and compared to profling obtained by the towed EdgeTech (West Ware- ham, Massachusetts) SB216S. Both refection losses and sub-bottom profles were found very close to the ground truth. A sub-bottom profle was derived from cross correlation of upward and downward-looking beams (MVDR beam- former) from the vertical array. Another profle was extracted from the chirp sub-bottom profler close to the location of the eFOLAGA (a profle was visually picked that seems to contain similar information as the noise, with a high vari- ability from profle to profle). The levels are adjusted arbi- trarily. Peaks from both noise and chirp sonar are present at about 23 meters (bathymetry), and there was a weaker return from both techniques at a depth of 26.5 meters into the sediment. Overall, the results demonstrated the capability of using AUVs equipped with a unique vertical line and tetrahedral compact acoustic array for estimating seabed properties in a cost- and time-effcient manner. However, CMRE is inves- electronic devices for navigation purposes were turned off, and only the data acquisition system was active. Some at- tempts were made to keep the vehicle at fxed depths by manually trimming the buoyancy and to perform a linear track at constant depth using the propeller for forward mo- tion. However, the behavior of the vehicle was not as expect- ed, and only the bottom-moored missions were considered. A small rubber boat with an outboard engine outftted with a portable GPS data recorder maneuvered in the vicin- ity of the array. It was detected through advanced processing of the volumetric array demonstrating that compact volu- metric arrays are effective tools for the detection of small surface craft. Volumetric array payload for small surface ship detection. Feb2014.indd 62 2/11/14 1:12 PM

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