1. Measurement of low-frequency underwater noise by a self-recording hydrophone Bong-Chae Kim, Hongsang Cho, Byoung-Nam Kim, Chang-Woong Shin, Donggoog Kim, and Bok Kyung Choi Marine Environment Research Department Korea Ocean Research & Development Institute

2. Objectives of this study To test a newly developed self-recording hydrophone to measure low-frequency underwater noise in the sea To acquire low-frequency ocean noise data at a site in the South Sea of Korea To investigate correlation between noise levels and environment variables

3. Block diagram and specifications of self-recording hydrophone

4. Receiving frequency characteristics of self-recording hydrophone

5. Self-recording hydrophone B&K 8103 hydrophone SD memory Battery

6. Measurement site KOREA JAPAN CHINA Yellow Sea East Sea Korea Strait ● site South Sea

7. Instruments installation for noise measurement Hydrophone (20 m) 10 m R/V Eardo Sea bed 52 m Hydrophone (40 m) ADCP 5 m Radar Anemometer Self-recording hydrophone Sea surface CTD

8. Recording and spectrum analysis system by conventional cabled hydrophone Instrumentation cassette recorder (Sony PC208Ax) Oscilloscope (LeCroy LT264M) Measuring amplifier (B&K 2636) Hydrophone (B& K 8106) Recording Personal computer A/D converter (NI PCI-6034E, 16bit) Spectrum analysis (DADiSP 2002) Spectrum analysis Instrumentation cassette recorder (Sony PC208Ax)

9. Environment variables

10. Averaged noise spectrum level

11. Mean and standard deviation of noise spectrum level

12. Correlation between wind speed and noise level (20 m depth) Correlation coefficient = 0.0323 Correlation coefficient = -0.1266

13. Correlation between wind speed and noise level (40 m depth) Correlation coefficient = 0.0286 Correlation coefficient = -0.2638

14. Correlation between wind speed and noise level (52 m depth) Correlation coefficient = 0.1435 Correlation coefficient = 0.0037

15. Correlation between current velocity and noise level (20 m depth) Correlation coefficient = 0.6555 Correlation coefficient = -0.1668

16. Correlation between current velocity and noise level (40 m depth) Correlation coefficient = 0.6303 Correlation coefficient = -0.4576

17. Correlation between current velocity and noise level (52 m depth) Correlation coefficient = -0.3027 Correlation coefficient = -0.0248

18. Summary A self-recording hydrophone was newly developed to use for measurement of low-frequency ocean noise. Low-frequency noise at a site of the South Sea of Korea was measured by using the self-recording hydrophone and conventional cabled hydrophones. The self-recording hydrophone is superior to the conventional cabled hydrophone to measure low-frequency underwater noise when in particular water flow is strong.

19. Thank you!