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U.S. Geological Survey Data Series 620

Archive of Digital Chirp Subbottom Profile Data Collected During USGS Cruise 08CCT01, Mississippi Gulf Islands, July 2008

By Arnell S. Forde,1 Shawn V. Dadisman,1 James G. Flocks,1 and Charles R. Worley2

1U.S. Geological Survey, St. Petersburg, FL 33701.
2U.S. Geological Survey, Woods Hole, MA 02543.

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).


Home | Acronyms | Contents | Navigation | Profiles | Logs | Metadata | Software


Page Contents (Set of 5 Discs):

Information Statement

System Requirements

Project Summary

Disc Organization

Getting Started

Acknowledgments

References Cited

Suggested Citation

Study area map

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, Adobe 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 interactive profiles are Internet Explorer 8 for Windows and Firefox 3.6 for all platforms


Project Summary

In July of 2008, the U.S. Geological Survey (USGS) conducted geophysical surveys to investigate the geologic controls on island framework from Ship Island to Horn Island, Mississippi, for the Northern Gulf of Mexico (NGOM) Ecosystem Change and Hazard Susceptibility project. Funding was provided through the Geologic Framework and Holocene Coastal Evolution of the Mississippi-Alabama Region Subtask (http://ngom.er.usgs.gov/task2_2/index.php); this project is also part of a broader USGS study on Coastal Change and Transport (CCT). This report serves as an archive of unprocessed digital Chirp seismic reflection data, trackline maps, navigation files, Geographic Information System (GIS) files, Field Activity Collection System (FACS) logs, observer's logbook, and formal Federal Geographic Data Committee (FGDC) metadata. 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, 08CCT01 tells us the data were collected in 2008 to study the Coastal Change and Transport (CCT) and the data were collected during the first field activity for that study in that calendar year. 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 Chirp system used during this survey produces a high resolution, shallow penetration (less than 50 ms) profile image beneath the seafloor. 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 1 displays the acquisition geometry. Refer to table 1 for a summary of acquisition parameters. See the digital FACS equipment log (47-KB PDF) for details about the acquisition equipment used. Table 2 lists trackline statistics.

The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y rev 1 (Norris and Faichney, 2002) format; 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 and USGS software for viewing the SEG-Y files (Zihlman, 1992). The processed SEG-Y data were also exported to Chesapeake Technology, Inc. (CTI) SonarWeb software to produce an interactive version of the profile that allows the user to obtain a geographic location and depth from the profile for a cursor position. This information is displayed in the status bar of the browser.

NOTE: If using Internet Explorer 8, Active Content/Active X controls must be disabled. Please refer to the details and setup page for more information.

For both browsers, the status bar and JavaScript must be enabled. Firefox also requires "Change status bar text" to be checked under Advanced JavaScript Settings. This option can be found on the main Toolbar under Tools > Options > Content (tab) > Advanced... >

Allow scripts to:

checkboxChange status bar text

Use of other browsers may result in spurious or no information given in the status window.

The printable and interactive profiles can be viewed from the Profiles page or from links on the trackline maps. Detailed information about the navigation system used can be found in table 1 and the FACS equipment log (47-KB PDF). To view the trackline maps and navigation files, and for more information about these items, see the Navigation page.

NOTE: An unknown software malfunction resulted in no SEG-Y data being recorded to the headers for lines 08i124 and 08i139 - 08i144.


Disc Organization

The Disc Contents page is a diagram with links to the locations of all files and folders contained on this disc; all discs are identical except for the SEG-Y files they contain.

Disc 1 contains SEG-Y files for lines 08i01 through 08i19; disc 2 contains SEG-Y files for lines 08i20 through 08i37a; disc 3 contains SEG-Y files for lines 08i38 through 08i63; disc 4 contains SEG-Y files for lines 08i64 through 08i108; and disc 5 contains SEG-Y files for lines 08i109 through 08i123; 08i125 through 08i138; 08i145 and 08i146.


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 G.K. Gilbert captain Richard Young of the USGS - St. Petersburg, FL for his assistance in data collection. This document was improved by the reviews of Xan Fredericks (Jacobs Technology Inc. - St. Petersburg, FL) and Kim Haag (USGS - Tampa, FL).


References Cited

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.

Zihlman, F.N., 1992, DUMPSEGY V1.0: A program to examine the contents of SEG-Y disk-image seismic data: U.S. Geological Survey Open-File Report 92-590, 28 p. Also available on-line at http://pubs.er.usgs.gov/usgspubs/ofr/ofr92590.


Suggested Citation

Forde, A.S., Dadisman, S.V., Flocks, J.G., and Worley, C.R., 2011, Archive of digital Chirp subbottom profile data collected during USGS cruise 08CCT01, Mississippi Gulf Islands, July 2008: U.S. Geological Data Series 620, 5 DVDs.


Home | Acronyms | Contents | Navigation | Profiles | Logs | Metadata | Software

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