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Ocean Current Effects on Marine Seismic Systems and Deployments.
Final rept. FY81,
NAVAL OCEAN RESEARCH AND DEVELOPMENT ACTIVITY NSTL STATION MS
Pagination or Media Count:
Upper level and near bottom current measurements were made near DSDP Hole 395A 22 degs. 45N, 46 degs. 10W in March-April 1981 in support of the at-sea test of the Marine Seismic System Project. Four upper ocean current profiles were made during initial deployment of the borehole seismometer. Readings were noticeably contaminated by ship motion, but clearly indicated a variable yet generally slow current regime which posed minimal threat of cable entanglement. Current measurements made 5 m off bottom during seismometer testing showed marked spectral peaks at semidiurnal and inertial frequencies. Mean speed of 4.4 cmsec and maximum speed of 9 cmsec were low but possibly of sufficient magnitude to cause contamination of concurrently deployed ocean bottom seismometer records with hydrodynamically generated noise. Other studies have confirmed noise contamination of OBS records by near bottom currents, with a possible 10 cmsec threshold for its importance. While methods to detect and eliminate the noise might be developed, instrument testing and redesign to reduce sensitivity to contamination is probably wiser.
APPROVED FOR PUBLIC RELEASE