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RECENT UNDERWATER SURVEYS USING LOW-FREQUENCY SOUND TO LOCATE SHALLOW BEDROCK

1958; Geological Society of America; Volume: 69; Issue: 1 Linguagem: Inglês

10.1130/0016-7606(1958)69[69

1943-2674

William O. Smith,

Underwater Vehicles and Communication Systems

Research Article| January 01, 1958 RECENT UNDERWATER SURVEYS USING LOW-FREQUENCY SOUND TO LOCATE SHALLOW BEDROCK W. O SMITH W. O SMITH U. S. GEOLOGICAL SURVEY, WASHINGTON, D. C. Search for other works by this author on: GSW Google Scholar Author and Article Information W. O SMITH U. S. GEOLOGICAL SURVEY, WASHINGTON, D. C. Publisher: Geological Society of America First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1958, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1958) 69 (1): 69–98. https://doi.org/10.1130/0016-7606(1958)69[69:RUSULS]2.0.CO;2 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation W. O SMITH; RECENT UNDERWATER SURVEYS USING LOW-FREQUENCY SOUND TO LOCATE SHALLOW BEDROCK. GSA Bulletin 1958;; 69 (1): 69–98. doi: https://doi.org/10.1130/0016-7606(1958)69[69:RUSULS]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Underwater investigations at Lake Mead, Chicago, Passamaquoddy Bay, and on Long Island established the characteristics of sound waves that can be used in shallow geophysical exploration by the sonar method.At Lake Mead the sediments were for the most part clay of high water content which was easily penetrated by low-power sound at a frequency of 14.2 kilocycles. The greatest depth of penetration was 140 feet. Sound having frequencies of 50 and 80 kilocycles did not penetrate. At Chicago, sound at a frequecy of 11 kilocycles and an output power of 800 watts gave a satisfactory delineation of bedrock beneath Lake Michigan. The maximum distance to bedrock was about 135 feet. At Passamaquoddy Bay a sound frequency of 6 kilocycles and about 700 watts of output power gave much better delineation of bedrock. A frequency of 6 kilocycles at the lower output power was much better than 11 kilocycles at higher power. About 250 feet of penetration was attained. Pulsed power was used in each of these investigations. The pulse lengths were long—about 14–25 milliseconds.Bedrock was mapped at Lake Mead, Chicago, and Passamaquoddy Bay. The methods of ordinary hydrographic surveying were used for horizontal and vertical positioning. For horizontal positions the ordinary three-point sextant-fix method was used. For vertical positioning, recording gages suitably placed and supplemented by staff gages were used. All data were tied into the third-order control net of the U. S. Coast and Geodetic Survey.In connection with a study for a proposed Midwestern waterway, the technical problem was reviewed and the techniques considerably improved. New equipment was built and evaluated on Long Island Sound. It operated with pulsed power at a frequency of 6 kilocycles, and pulse length was controlled and variable from 1 to 9 milliseconds. Output acoustic power was about 2500 watts. With the transducer in ordinary operating positions as much as 400 feet of sediment was penetrated. With the transducer placed directly on the bottom of the water in Huntington Bay about 750 feet of penetration was attained. Several innovations in sonar techniques, which are desirable for sediment exploration, and which give much more detailed information than the earlier equipment are described.The techniques required for stratigraphic interpretation of the sound records are described briefly. A method for the determination of sound velocities is discussed. Multiple echoes and other effects complicate the interpretation of records and are explained. The problems of geological control encountered also are mentioned. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.