Analysis and Ranking of the Acoustic Disturbance Potential of ...

Report No. 6945
BBN Systems and Technology Corporation
APPENDIX B:
ANALYSIS OF ICEBREAKING SOUNDS*
B.l
Introduction
The drillship CANMAR EXPLORER I1 was drilling an exploratory well at the
Corona drillsite in early September 1986. Corona is in the Alaskan Beaufort
Sea, north of Camden ~ a northwest ~ , of Barter Island, about 22 n mi offshore
where the water depth is 35 m. As part of a planned, comprehensive sound
monitoring effort, recordings were made of the underwater sounds from the
support vessel ROBERT LEMEUR while it was icebreaking. In particular, sounds
were recorded continuously for 14 minutes at range 0.25 n mi (0.46 km) .
A detailed report of the sound monitoring results was published (Greene.
1987), but not every interest in the recorded data was recognized during the
original analysis. For instance, although the sound levels vs distance from
the icebreaker were analyzed and reported, no extended time series of sound
levels from icebreaking were investigated. In assessing the possible impact
of such sounds of wildlife, knowledge of the variation in sound levels with
time might be important. Hence, additional analysis has been performed on the
14 minute segment of icebreaking sounds, range 0.25 n mi.
B.2 Methods
The R/V JUDY ANN, a 43-ft fishing boat, had been chartered to serve as a
sound boat for underwater acoustical measurements of the drillship and its
support vessels. The boat's engines were shut down during recording.
Hydrophones made by International Transducer Corporation (model 6050C) were
suspended beneath a lightly-tethered sparbuoy at depths 9, 18, and 30 m. the
hydrophones included a low-noise preamplifier and had a flat receiving
response from below 20 Hz to above 8 kHz. The in-water cables were faired to
prevent strumming. Signals from the three hydrophones were further amplified,
if necessary, to obtain the best dynamic range on the tape recorder. the
p.ostamplifier gains could be set in steps of 10 dB from 0 to 40 dB. The audio
cassette tape recorder was a four-channel Fostex model 250. The sound
"Charles R. Greene, Jr., Greeneridge Sciences, Inc.