1. Listening to the Sound: Ambient Noise in Admiralty Inlet

2. Motivation Study ambient noise and identify sources
Results used by regulators in permitting process

3. Site
Admiralty Inlet b/w
Port Townsend and
Whidbey Island

4. Data Collection Temporal Data Spatial Data -Three month sea
spider deployments
- Samples at 80 kHz.
Spatial Data
Deployment from
R/V deck during cruises
-Samples at 400 kHz

5. Typical Sources
G. Wenz, 1962 identifies typical sources of ambient noise in deep water
freq < 100 Hz:
turbulent pressure fluctuations, seismic activity, explosions
10 – 10,000 Hz:
ships, industrial activity
100 – 50,000 Hz:
bubbles and spray, weather

6. Data Processing Basic Algorithm Raw voltage data is tapered
FFT on tapered data
FFT output to power spectral density
Apply calibration curve
Ensemble averages

7. Recording Hydrophone Results
Spectra chosen to represent different acoustic conditions at the site.

8. Recording Hydrophone Results
Spectrograms combine data in from individual spectra into a time series.
Other ship traffic
Ferry crossings
June 15th, 2009 Spectrogram

9. Recording Hydrophone Results
Sound Pressure Level (SPL) is obtained by integrating under the PSD curve
June 15th, 2009 SPL Time Series

10. Recording Hydrophone Results
Cumulative Probability Density Function for May-August mobile hydrophone deployment

11. Recording Hydrophone Results
SPL and velocity time series data for May-August deployment

12. Recording Hydrophone Results
SPL and depth averaged velocity time series for May 25th

13. Recording Hydrophone Results
SPL vs. depth averaged velocity. Error bars represent two std. deviations.
Error bars represent two standard deviations.

14. Recording Hydrophone Results
Permanent Noise Levels for depth averaged velocity bins.
Flood
Ebb
Depth Ave.
Velocity (m/s)
Total SPL
(dB re 1 μPa)
Per. Noise
112.8 ± 13.1
99.7
112.6 ± 13.3
99.3
115.7 ± 12.0
103.7
114.0 ±12.4
101.6
124.3 ± 10.8
113.5
118.7 ± 8.8
109.9
132.8 ± 8.3
124.5
126.5 ± 7.5
119.0
138.9 ± 6.9
132.0
133.1 ± 6.5
126.6
142.7 ± 3.8
138.9
± 6.1
132.1 -
3.0 <
141.3 ± 4.1
137.2

15. Mobile Hydrophone Surveys
Surveys taken in concentric circles around site at 0m, 500m, 1000m, 1500m, 2000m, and 2500m
Surveys taken a 3m, 25m, and 50m below the surface
Purpose is to search for patterns in spatial variations near the site.

16. Mobile Hydrophone Results
Selected spectra demonstrate different conditions:
Survey 10: Recreational boat near site (closest during 25m survey)
- Survey 7: Quiet conditions

17. Mobile Hydrophone Results
Mobile hydrophone survey map

18. Conclusions Stationary Hydrophone Surveys Mobile Hydrophone Surveys
Stationary surveys demonstrate clear dependence on tidal currents
Anthropogenic noise (ship traffic) also causes regular increases in spectral levels and SPLs
Mobile Hydrophone Surveys
Mobile hydrophones show no spatial patterns
High resolution spectra and notes taken during surveys demonstrate impact of known anthropogenic noise sources on the acoustic environment

19. Ongoing Analysis
Study impact of turbulent pressure fluctuations (psuedo sound) on recorded spectral levels
- This is also called “flow noise”
Seasonal variations?
Use AIS to identify contributions from ship traffic

20. Ongoing Analysis
Study feasibility of using the recording hydrophone in detecting cetacean vocalizations
Example Orca Vocalization
Acoustic Release

21. Acknowledgements Project funding provided by SnoPUD
Joe Talbert for his fantastic equipment engineering
Everybody in the CEE EFM lab
Dr. Thomson and Dr. Polagye