Appendix C
Comparison of Yearly Sound Energy from Oceanographic Research and Supertankers

Although the duration of the transmission in a typical oceanographic experiment varies depending on the experiment, a total broadcast time of 100 hours would be longer than most experiments. We will assume that 10 such experiments are conducted each year. The total yearly energy in a 1-Hz band produced by 10 typical oceanographic experiments would be about 66 dB higher than the average sound level [10 log (60×600×100×10) = 65.6 dB]. The sound levels generated by oceanographic experiments vary greatly. An average level is probably near 200 dB (re 1 µPa—water standard). The entire sonic energy generated by these 10 oceanographic surveys is, therefore, about 266 dB (re 1 µPa—water standard) in the frequency region near 50 Hz.

There are about 127 supertankers presently operating in the oceans of the world at any one time.1 At its typical speed of 15 to 22 knots, the average supertanker produces a source level (calculated at 1 m from the source) having a spectrum level (energy in a 1-Hz band) of about 187 dB at 50 Hz and about 232 dB at 2 Hz (re 1 µPa—water standard) (personal communication, Joal J. Newcomb to the Committee on Low-frequency Sound and Marine Mammals, 1993). There is considerable variability in the noise levels generated by different

1  

 Joal J. Newcomb, Code 7176, Naval Research Laboratory, Stennis Space Center, Mississippi 39529.



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--> Appendix C Comparison of Yearly Sound Energy from Oceanographic Research and Supertankers Although the duration of the transmission in a typical oceanographic experiment varies depending on the experiment, a total broadcast time of 100 hours would be longer than most experiments. We will assume that 10 such experiments are conducted each year. The total yearly energy in a 1-Hz band produced by 10 typical oceanographic experiments would be about 66 dB higher than the average sound level [10 log (60×600×100×10) = 65.6 dB]. The sound levels generated by oceanographic experiments vary greatly. An average level is probably near 200 dB (re 1 µPa—water standard). The entire sonic energy generated by these 10 oceanographic surveys is, therefore, about 266 dB (re 1 µPa—water standard) in the frequency region near 50 Hz. There are about 127 supertankers presently operating in the oceans of the world at any one time.1 At its typical speed of 15 to 22 knots, the average supertanker produces a source level (calculated at 1 m from the source) having a spectrum level (energy in a 1-Hz band) of about 187 dB at 50 Hz and about 232 dB at 2 Hz (re 1 µPa—water standard) (personal communication, Joal J. Newcomb to the Committee on Low-frequency Sound and Marine Mammals, 1993). There is considerable variability in the noise levels generated by different 1    Joal J. Newcomb, Code 7176, Naval Research Laboratory, Stennis Space Center, Mississippi 39529.

OCR for page 74
--> vessels, but the level just given is the average. The total yearly energy in a 1-Hz band produced by the supertanker fleet is 96 dB higher than the average for a single vessel [10 log (60×60×24×365×127) = 96.03 dB]. The entire sonic energy generated by the fleet of super-tankers is, therefore, about 283 dB near 50 Hz and about 328 dB near 2 Hz (dB re 1 µPa—water standard).