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Archive of Digital Chirp Subbottom Profile Data Collected During USGS Cruises 09CCT03 and 09CCT04, Mississippi and Alabama Gulf Islands, June and July 2009

By Arnell S. Forde,¹ Shawn V. Dadisman,¹ James G. Flocks,¹ and Dana S. Wiese¹

¹U.S. Geological Survey, St. Petersburg, FL 33701.

U.S. Department of the Interior
U.S. Geological Survey
St. Petersburg Coastal and Marine Science Center

Publications are available from USGS Information Services, Box 25286, Federal Center, Denver, CO 80225-0046 (telephone 1-888-ASK-USGS; e-mail: infoservices@usgs.gov).

	Page Contents (Set of 6 Discs): Information Statement System Requirements Project Summary Disc Organization Getting Started Acknowledgments References Cited Suggested Citation

Information Statement

This Digital Versatile Disc (DVD) publication was prepared by an agency of the United States Government. Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied is made regarding the display or utility of the data on any other system, nor shall the act of distribution imply any such warranty. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the data described and (or) contained herein. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof.

System Requirements

This disc is readable on any computing platform that has standard DVD driver software installed. The minimum software requirements are a Web browser, a portable document format (PDF) reader, and a text editor. If you cannot fully access the information on this page, please contact USGS Information Services at infoservices@usgs.gov or 1-888-ASK-USGS. NOTE: The only supported Web browsers that properly display all features of the geospatial profiles are Internet Explorer 8 or greater for Windows and Firefox 3.6 or greater for all platforms

Project Summary

In June and July of 2009, the U.S. Geological Survey (USGS) conducted geophysical surveys to investigate the geologic controls on island framework from Cat Island, Mississippi, to Dauphin Island, Alabama, as part of a broader USGS study on Coastal Change and Transport (CCT). The surveys were funded through the Northern Gulf of Mexico Ecosystem Change and Hazard Susceptibility Project as part of the Holocene Evolution of the Mississippi-Alabama Region Subtask (http://ngom.er.usgs.gov/task2_2/index.php). This report serves as an archive of unprocessed digital Chirp seismic profile data, trackline maps, navigation files, Geographic Information System (GIS) files, Field Activity Collection System (FACS) logs, and formal Federal Geographic Data Committee (FGDC) metadata. Single-beam and Swath bathymetry data were also collected during these cruises and will be published as a separate archive. Gained (a relative increase in signal amplitude) digital images of the seismic profiles are also provided. Refer to the Acronyms page for expansion of acronyms and abbreviations used in this report.

The USGS St. Petersburg Coastal and Marine Science Center (SPCMSC) assigns a unique identifier to each cruise or field activity. For example, 09CCT03 and 09CCT04 tell us the data were collected in 2009 to study Coastal Change and Transport (CCT) and the data were collected during the third and fourth field activities for that study in that calendar year. Cruise 09CCT03A survey data were also collected as a subset during cruise 09CCT03; this dataset is restricted to Cat Island, MS, and consists of lines 09c627 to 09c695. Although listed as a separate cruise in this archive and on the FACS forms, it was not officially assigned a unique ID by the SPCMSC. This naming convention was adopted in the field to help distinguish this smaller cruise from the larger one during the data acquisition and archival processes. Refer to http://walrus.wr.usgs.gov/infobank/programs/html/definition/activity.html for a detailed description of the method used to assign the field activity identification (ID).

All Chirp systems use a signal of continuously varying frequency; the EdgeTech SB-512i and SB-424 Chirp systems used during these surveys produce high resolution, shallow penetration (less than 50 ms) profile images beneath the seafloor. Cruises 09CCT03 and 09CCT03A both collected SB-424 data and 09CCT04 collected SB-512i data. The towfish is a sound source and receiver, which is typically towed 1 - 2 m below the sea surface. The acoustic energy is reflected at density boundaries (such as the seafloor or sediment layers beneath the seafloor), detected by a receiver, and recorded by a PC-based seismic acquisition system. This process is repeated at timed intervals (for example, 0.125 s) and recorded for specific intervals of time (for example, 50 ms). In this way, a two-dimensional vertical image of the shallow geologic structure beneath the ship track is produced. Figure 1A and 1B display the acquisition geometries. Refer to table 1 for a summary of acquisition parameters. See the digital FACS folder equipment files for details about the acquisition equipment used. Table 2 lists trackline statistics for cruise 09CCT03 and table 3 lists statistics for cruise 09CCT04.

The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y rev 0 (Barry and others, 1975) format instead of the newer rev 1 format (Norris and Faichney, 2002); the first 3,200 bytes of the card image header is in ASCII format instead of EBCDIC format. The SEG-Y files may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU) (Cohen and Stockwell, 2010). See the How To Download SEG-Y Data page for download instructions. The web version of this archive does not contain the SEG-Y trace files. These files are very large and would require extremely long download times. To obtain the complete DVD archive, contact USGS Information at 1-888-ASK-USGS or infoservices@usgs.gov. The printable profiles provided here are GIF images that were processed and gained using SU software; refer to the Software page for links to example SU processing scripts. The processed SEG-Y data were also exported to Chesapeake Technology, Inc. (CTI) SonarWeb software to produce a geospatially interactive version of the profile that allows the user to obtain a geographic location and depth from the profile for a given cursor position. This information is displayed in the status bar of the browser.

The printable and geospatial profiles can be viewed from the Profiles page. Detailed information about the navigation system used can be found in table 1 and the FACS logs. To view the trackline maps and navigation files, and for more information about these items, see the Navigation page.

NOTE: As a result of either generator failure or an unknown software malfunction, no SEG-Y data were recorded for lines 09c653, 09c654, 09c655, 09c657, 09c667, 09c668, 09c669, 09c670, 09c676, 09c694 of cruise 09CCT03 and line 09i31 of cruise 09CCT04.

Disc Organization

The Disc Contents page is a diagram with links to the locations of all files and folders contained on this disc; all five discs are identical except for the SEG-Y files they contain. Lines 09c500 - 09c695 were collected during 09CCT03 and lines 09i01 - 09i54 during 09CCT04.

Disc 1 contains SEG-Y files for lines 09c500 through 09c519; disc 2 contains SEG-Y files for lines 09c520 through 09c570a; disc 3 contains SEG-Y files for lines 09c571 through 09c606; disc 4 contains SEG-Y files for lines 09c607 through 09c644; disc 5 contains SEG-Y files for lines 09c645 through 09c695 and 09i01 through 09i03; disc 6 contains SEG-Y files for lines 09i04 through 09i54.

Getting Started

To access the information contained on this disc, use a Web browser to open the file index.html. This report is divided into seven sections: Acronyms and Abbreviations, Disc Contents, Navigation Data and Maps, Seismic Profiles, Field Activity Logs, FGDC Metadata, and Software. Links at the top and bottom of each page provide access to these sections. This report contains links to the USGS and collaborators or other resources that are accessible only if access to the Internet is available while viewing these documents.

Acknowledgments

Funding and (or) support for this study was provided by the USGS Coastal and Marine Geology Program. We thank R/V Survey Cat captains Nancy DeWitt and B.J. Reynolds and R/V G.K. Gilbert captain Rich Young of the USGS - St. Petersburg, FL for their assistance in data collection. We would also like to thank Elizabeth Pendleton of the USGS Coastal and Marine Science Center - Woods Hole, MA, for her help in data processing. This document was improved by the reviews of Mark Hansen (USGS - SPCMSC) and Jamie Bonisteel-Cormier (Jacobs Technology Inc. - St. Petersburg, FL).

References Cited

Barry, K.M., Cavers, D.A., and Kneale, C.W., 1975, Recommended standards for digital tape formats: Geophysics, v. 40, no. 2, p. 344-352. Also available on-line at http://www.seg.org/resources/publications/misc/technical-standards.

Cohen, J.K., and Stockwell, J.W., Jr., 2010, CWP/SU: Seismic Unix Release 41: A free package for seismic research and processing: Center for Wave Phenomena, Colorado School of Mines. Available on-line at http://www.cwp.mines.edu/cwpcodes/.

Norris, M.W., and Faichney, A.K. (eds.), 2002, SEG Y rev 1 Data Exchange format: Society of Exploration Geophysicists. Also available on-line at http://www.seg.org/resources/publications/misc/technical-standards.

Suggested Citation

Forde, A.S., Dadisman, S.V., Flocks, J.G., and Wiese, D.S., 2011, Archive of digital Chirp subbottom profile data collected during USGS cruises 09CCT03 and 09CCT04, Mississippi and Alabama Gulf Islands, June and July 2009: U.S. Geological Data Series 590, 6 DVDs.