Page 38: of Marine Technology Magazine (November 2017)

ADCPs

ADCP was deployed in 36m of water at Janus con? guration, with beam ? ve in readings were recorded by the ADCP’s a site off the west coast of Ireland dur- the vertical and beams one-four offset at onboard micro electromechanical sys- ing the winter of 2015 (the experiment some prede? ned angle from the vertical. tems (MEMS) accelerometers.

was repeated during the winters of 2016 For this deployment, the Janus angle Velocities and backscatter intensity and 2017), with the aim of gathering ac- was 25 (degrees) and 34 bins, each sep- were recorded along the ? ve beams curate wave measurements in extreme arated by 1.2 m from center to center, continuously at 2 Hz for three months. conditions. were selected along each beam. Continuous sampling enabled the cap-

The Sentinel V was gimbal-mounted The nominal vertical distances from ture of details of several giant events and housed within a trawler-resistant the ADCP transducer head to the centers with crest-to-trough heights more than frame and secured to the seabed in an of the ? rst and last bin were approxi- 22m. Several theoretical explanations upward-looking con? guration. The Sen- mately 26m and 66m, respectively, giv- have been proposed for such extreme tinel V is one of the latest in a line of ing an effective range of measurement waves, in particular modulational insta-

ADCP developed by TRDI. It utilizes from about 10m below to 30m above bility and directional focusing. Typical sonar pulses along ? ve beams to gather the Mean Water Level (MWL). In addi- oceanic wind seas are short-crested, or measurements of both orbital veloc- tion to Doppler readings, pressure was multidirectional, wave ? elds and their ity and echo intensity at predetermined recorded by the Sentinel Vs onboard dynamics is more ‘free’ than the 1D distances (bins) along each beam. The sensor. The Sentinel V had on board ‘long-wave-guide’ counterpart. Indeed, ? ve beams are arranged in the so-called a 16GB memory card. Pitch and Roll energy can spread directionally and as

November/December 2017 38

MTR

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