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Data Series 856


Archive of Digital Chirp Subbottom Profile Data Collected During USGS Cruise 12BIM03 Offshore of the Chandeleur Islands, Louisiana, July 2012

By Arnell S. Forde, Jennifer L. Miselis, and Dana S. Wiese

U.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).


Index | Home | Abbreviations | Contents | Navigation | Profiles | Logs | Metadata | Software


Page Contents:

Information Statement

System Requirements

Getting Started

Disc Organization

Project Summary

Acknowledgments

References Cited

Suggested Citation

Study Area Map
Figure 1. Regional (inset) and location map showing the July 2012 geophysical survey area, offshore of the Chandeleur Islands, La., during U.S. Geological Survey field activity 12BIM03.

Information Statement

This Digital Versatile Disc (DVD) publication was prepared by an agency of the United States Government. Although these data were 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.


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: Abbreviations, Disc Contents, Navigation Data and Maps, Subbottom 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 U.S. Geological Survey (USGS) and collaborators or other resources that are only accessible if access to the Internet is available while viewing these documents.


Disc Organization

This disc contains a readme (2-KB text file) document, which provides a brief description of the report; a folder containing SEG Y format binary data files; GIS files; and all the Hypertext Markup Language (HTML) files, folders, and images used to produce the Web pages included in this report. The Disc Contents page contains a diagram with locations and links to all files and folders contained on this disc.


Project Summary

From July 23 - 31, 2012, the U.S. Geological Survey conducted geophysical surveys to investigate the geologic controls on barrier island framework and long-term sediment transport along the oil spill mitigation sand berm constructed at the north end and just offshore of the Chandeleur Islands, La. (figure 1). This effort is part of a broader USGS study, which seeks to better understand barrier island evolution over medium time scales (months to years). This report serves as an archive of unprocessed digital chirp subbottom data, trackline maps, navigation files, Geographic Information System (GIS) files, Field Activity Collection System (FACS) logs, and formal Federal Geographic Data Committee (FGDC) metadata. Gained (showing a relative increase in signal amplitude) digital images of the seismic profiles are also provided. Refer to the Acronyms page for expansions 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, 12BIM03 tells us the data were collected in 2012 during the third field activity for that project in that calendar year and BIM is a generic code, which represents efforts related to Barrier Island Mapping. 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 ID.

All chirp systems use a signal of continuously varying frequency; the EdgeTech SB-424 system used during this survey produces high-resolution, shallow-penetration (typically less than 50 milliseconds (ms)) profile images of sub-seafloor stratigraphy. The towfish contains a transducer that transmits and receives acoustic energy and is typically towed 1 - 2 m below the sea surface. As transmitted acoustic energy intersects density boundaries, such as the seafloor or sub-surface sediment layers, energy is reflected back toward the transducer, received, and recorded by a PC-based seismic acquisition system. This process is repeated at regular time intervals (for example, 0.125 seconds (s)) and returned energy is recorded for a specific duration (for example, 50 ms). In this way, a two-dimensional (2-D) vertical image of the shallow geologic structure beneath the ship track is produced. Figure 2 displays the acquisition geometry. Refer to table 1 for a summary of acquisition parameters and table 2 for trackline statistics.

The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG Y rev. 0 format (Barry and others, 1975); the first 3,200 bytes of the card image header are 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 Services 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 and can be viewed from the Profiles page or from links located on the trackline maps; refer to the Software page for links to example SU processing scripts. The SEG Y files are available on the DVD version of this report or on the Web, downloadable via the USGS Coastal and Marine Geoscience Data System (http://cmgds.marine.usgs.gov). The data are also available for viewing using GeoMapApp (http://www.geomapapp.org) and Virtual Ocean (http://www.virtualocean.org) multi-platform open source software.

Detailed information about the navigation system used can be found in table 1 and the Field Activity Collection System (FACS) logs. To view the trackline maps and navigation files, and for more information about these items, see the Navigation page.

NOTE: Due to system malfunctions, subbottom data collection did not actually begin until July 26, 2012. Bathymetry and backscatter data were also collected concurrently during this survey and the data is available in a separate report (DeWitt and others, 2013).

Acknowledgments

Funding for this study was provided by the USGS Coastal and Marine Geology Program. We thank Research Vessel (R/V) Survey Cat captain Nancy DeWitt of the USGS SPCMSC for her assistance in data collection and Will Pfeiffer and Julie Bernier for their assistance with bathymetry data processing. This document was improved by the reviews of Kyle Kelso and Ellen Raabe of the USGS - St. Petersburg, Fla.

Disc Image Credit: Descloitres, J., MODIS Land Rapid Response Team at the NASA Goddard Space Flight Center, 2001, Louisiana.A2001361.1640.250m.jpg, accessed on May 13, 2014 at http://visibleearth.nasa.gov/view_rec.php?id=2364.


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 at https://dx.doi.org/10.1190/1.1440530.]

Cohen, J. K. and Stockwell, Jr. J. W., (2010), CWP/SU: Seismic Un*x Release No. 41: an open source software package for seismic research and processing, Center for Wave Phenomena, Colorado School of Mines, accessed on May 13, 2014 at http://www.cwp.mines.edu/cwpcodes/.

DeWitt, N.T., Miselis, J.L., Bernier, J.C., Reynolds, B.J., Wiese, D.S., Kelso, K.W., and Pfeiffer, W.R., 2014, Coastal bathymetry and backscatter data collected in 2012 from the Chandeleur Islands, Louisiana: U.S. Geological Survey Data Series 847, 1 DVD.

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., accessed on May 13, 2014 at http://pubs.er.usgs.gov/usgspubs/ofr/ofr92590.


Suggested Citation

Forde, A.S., Miselis, J.L., and Wiese, D.S., 2014, Archive of digital chirp subbottom profile data collected during USGS cruise 12BIM03 Offshore of the Chandeleur Islands, Louisiana, July 2012: U.S. Geological Survey Data Series 856, 1 DVD, available at https://dx.doi.org/856.


Index | Home | Abbreviations | Contents | Navigation | Profiles | Logs | Metadata | Software

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