Ocean Current Effects on Marine Seismic Systems and Deployments.

• Main Author: Boyd,Janice D
• Other Authors: NAVAL OCEAN RESEARCH AND DEVELOPMENT ACTIVITY NSTL STATION MS
• Format: Text
• Language: English
• Published: 1982
• Subjects: Physical and Dynamic Oceanography; Acoustics; Fluid Mechanics; *Ocean currents; North Atlantic Ocean; Surface waters; Ocean bottom; Velocity; Azimuth; Variations; Measurement; Underwater sound; Noise(Sound); Interference; Seismometers; Cylindrical bodies; Vibration; Deep sea drilling project; Strumming; North Atlantic
• Online Access: http://www.dtic.mil/docs/citations/ADA114135; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA114135

Upper level and near bottom current measurements were made near DSDP Hole 395A (22 degs. 45'N, 46 degs. 10'W) 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 cm/sec and maximum speed of 9 cm/sec 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 cm/sec 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.