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Measuring Changes in Ambient Noise Levels from the Installation and Operation of a Surge Wave Energy Converter in the Coastal Ocean

Study Status: 
Princple Investigator Contact Information: 

Name: Sarah Henkel

Address: Oregon State University, 2030 Marine Science Drive, Newport, OR 97365

Email: sarah.henkel@oregonstate.edu

Project Description: 

This project included 2 techniques for passive acoustic data collection: 1) campaign style deployments of fixed hydrophone lander stations to capture temporal variations in noise levels and 2) a drifting hydrophone system to record spatial variations within the project site. The hydrophone lander deployments were effective and economically feasible for enabling robust temporal measurements of ambient noise levels in a variety of sea state conditions.

Funding Source: 

This material is based upon work supported by the Department of Energy under Award Number DE-EE0006387.

Location of Research: 

Camp Rilea, Oregon

Project Aims: 
  1. Quantitative measurements of broadband (10Hz – 13 kHz) sound pressure levels before and during the installation and operation of a surge type wave energy conversion (WEC) device in the shallow coastal waters off the north Oregon coast
  2. Time/frequency characterizations of noise emissions surrounding the project through a variety of environmental conditions
  3. Evaluation of ambient noise levels measured during WEC construction and operation within the framework of baseline recordings taken in the area
  4. Quantitative comparisons of WEC generated noise emissions with natural and anthropogenic acoustic sources found near the project site.
Project Progress: 


Key Findings: 

Fixed and mobile acoustic recordings show the shallow waters of the nearshore region off Camp Rilea are dominated by the natural processes of breaking surf and wind wave generated sounds. Despite concerns that surf noise may saturate acoustic recordings in close proximity to the wave breaking zone, our results indicate that when using the instrumentation and approach presented here there is sufficient dynamic range to record and characterize surgeWEC generated acoustic emissions in the shallow waters off Camp Rilea, OR with a 16 bit hydrophone system. Flow noise is shown to be a confounding factor for acoustic energy in frequencies below 500 Hz during the range of environmental conditions presented here at fixed hydrophone receiver station depths of 10 – 13 m. Nevertheless, at a range of ~ 150 m, acoustic emissions from WECs in frequencies ranging from 500 Hz up to our system cutoff at 13 kHz can be recorded, identified and reliably quantified if they are of sufficient source level. During calmer conditions, surgeWEC signals should be characterized and measured for frequencies below 500 Hz during periods manually identified to be devoid of flow noise contamination. Previous acoustic recordings around deployed WECs (Polagye et al., 2017a; Polagye et al., in review) show similar low frequency limitations regarding flow noise contamination with fixed hydrophone recorders. For example, despite deeper water depths (30 m & 60 m) at the WETS facility which help to reduce wave orbital velocities and therefore affected flow noise frequencies compared to Camp Rilea (10 m), acoustic measurements from fixed hydrophones of low frequency WEC generated signals (hundreds of Hz) had to avoid periods of elevated flow noise linked with higher energy, longer period swell.

Related Publications: 

Henkel, S.; Haxel, J. (2017). Measuring Changes in Ambient Noise Levels from the Installation and Operation of a Surge Wave Energy Converter in the Coastal Ocean. Report by Oregon State University. pp 17. https://tethys.pnnl.gov/publications/measuring-changes-ambient-noise-levels-installation-and-operation-surge-wave-energy

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