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ABSTRACT

Underwater sounds from the semisubmersible drilling rig SEDCO 708 were recorded during drilling operations in the Aleutians on 29 September 1982. The objective of the study, funded by the American Petroleum Institute, was to quantify the rig sounds in terms of acoustic pressure and frequency. The results were needed to assess the spatial extent of the radiated noise and the associated acoustic influence on marine mammals. The water depth was 114 m. Recordings were made at ranges of 0.1, 0.2, 0.5, 1, 2, 5, and 10 nm at depths of 2.5, 5, 10, and 30 m. Recordings were also made at depths of 10 and 30 m, range 0.5 nm, to the south, west, north and east of SEDCO 708 to test for azimuthal dependencies. The results showed that numerous tonal components of sounds were received as far as 10 nm, although they were not strong. Broadband components were generally down to background levels for ranges of 1 nm and greater. Background levels were estimated to be from 102 to 112 dB//luPa for the 10 to 4000 Hz band and from 72 to 79 dB//luPa /Hz at 100 Hz. Source levels for tones at 60, 181, and 301 Hz are estimated to be 149, 137, and 136 dB//luPa-m, respectively. The source levels for the 10-500 and 80-4000 Hz bands are both estimated to be 154 dB//luPa-m. The variations with azimuth are on the same order as temporal variations. Signal level generally increased with depth, especially for low frequencies.