Underwater noise measurements of a 1/7th scale wave energy converter

Field measurements of the underwater acoustic signature of Columbia Power Technologies (Columbia Power) SeaRay wave energy converter (WEC) prototype are presented. The device was deployed in the vicinity of West Point (Puget Sound, Washington State) at a depth of approximately 20 meters. The 1/7
^th
scale SeaRay prototype is a heave and surge, point absorber secured to the seabed with a three-point mooring. Acoustic measurements were made in order to satisfy permit requirements and assure that marine life is not adversely affected. A series of one-minute hydrophone recordings were collected on March 30, 2011 for approximately 4 hours. During these recordings, significant wave height varied from 0.4 to 0.7 m, peak wave periods varied from 2.9 to 3.2 seconds, and southerly winds varied from 5 to 10 m s
^-1
. These are approximately twice the amplitude of typical operating conditions for the SeaRay in Puget Sound. Shipping vessel and ferry traffic levels also were typical. Received sound pressure levels during the experiment vary from 116 to 132 dB re 1 μPa in the integrated bands from 20 Hz to 20 kHz. At times, ship traffic dominates the signal, as determined from spectral characteristics and vessel proximity. Received sound pressure levels attributed to the WEC cycle from 116 to 126 dB re 1 μPa in the integrated bands from 60 Hz to 20 kHz at distances from 10 to 1500 m from the SeaRay. The cycling is well correlated with the peak wave period, including peaks and harmonics in the pressure spectral densities. Masking by ship noise prevents rigorous extrapolation to estimate the WEC source level at the conventional 1 m reference.