Aubrey L. Anderson
Acoustic Characterization of the Seafloor
Michael E. Duncan (MS student)
What are the capabilities and limitations of commonly available acoustic techniques for seafloor high resolution remote characterization in the greater water depths of OTRC interest: 6,000 to 10,000 feet. What new system design, operational configuration and/or signal analysis methods might significantly enhance the capability of the systems for qualitative or quantitative characterization and for seafloor structure design and safety assessment.
The focus on theme site investigation by the seafloor/structures thrust area is being followed in this project by application of the methods and test procedures for surveying the theme sites. This is being closely coupled with seafloor sampling by another project of the thrust area and will be related to uses of probes and shear wave measurements by third and fourth projects of the thrust area. The capabilities of remote sensing systems are investigated by computer simulations, by the design and carrying out of field surveys, most recently to the theme sites selected for OTRC characterization, and by analysis and interpretation of the resulting acoustic system records. This approach was initiated in a project preceding the present one wherein such simulations and measurements were made to address the feasibility of remote gas hydrate detection. The present project is applying the approach to investigate qualitative high resolution capabilities of remote sensing systems and to investigate the feasibility of quantitative description of seafloor layers remotely.
We maintain strong interaction and collaboration with the other forefront groups who are developing and applying shallow (subbottom) seafloor characterization including the Naval Research Laboratory (NRL) developers of the Acoustic Sediment Classification System (ASCS), the Florida Atlantic University developers of the Full Spectrum Sonar (CHIRP), and the NRL measurement program: Coastal Benthic Boundary Layer Special Research Project (CBBLSRP).
The increased knowledge of both qualitative and quantitative, high resolution characterization of the upper (shallow subbottom depths) seafloor by acoustic remote sensing should contribute directly to evaluation of potential sites for seafloor structures prior to foundation borings and should, together with seafloor borings and other sampling and measurement tools, address the issue of the distance over which a boring and the resultant foundation design could be extrapolated.
October 1992 to September 1997
A list of theme sites in the depth range of interest for detailed investigation. Data and interpretation of results of theme site surveys. Assessment of system and analysis capabilities based on survey results. Improved survey plans for subsequent theme site surveys. Site characteristics models for each site surveyed. Geoacoustic description of each site surveyed.
"Remote characterization of the seafloor including gassy and hydrated sediment regions" Aubrey L. Anderson, Proceedings of the Second International Offshore and Polar Engineering Conference, San Francisco, CA, 14-19 June, 1992.
" Hydrate occurrences in shallow subsurface cores from continental slope sediments" James M. Brooks, Aubrey L. Anderson, Roger Sassen, Ian R. MacDonald, Mahlon C. Kennicutt II, and Norman L. Guinasso, Jr., International Conference on Natural Gas Hydrates, Volume 715 of the Annals of the New York Academy of Sciences, April 1994.