U.S. Geological Survey Data Series 95

Archive of Digital Boomer and Chirp Seismic Reflection Data Collected During USGS Cruises 01RCE05 and 02RCE01 in the Lower Atchafalaya River, Mississippi River Delta, and Offshore Southeastern Louisiana, October 23-30, 2001, and August 18-19, 2002

U.S. Geological Survey Data Series 95

By Karynna Calderon,1 Shawn V. Dadisman,2 Jack L. Kindinger,2 James G. Flocks,2 Nicholas F. Ferina,1 and Dana S. Wiese2

1ETI Professionals, Inc., St. Petersburg, FL 33701.
2U.S. Geological Survey, St. Petersburg, FL 33701.

U.S. Department of the Interior
U.S. Geological Survey
Florida Integrated Science Center - Coastal and Watershed Studies

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


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Table of Contents:
Study Area Map

Information Statement

This DVD publication was prepared by an agency of the United States Government. Neither the United States Government nor any agency thereof nor any of their employees makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed in this report or represents that its use would not infringe privately owned rights. Reference therein 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.

Although all data and software published on this DVD have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and related materials and (or) the functioning of the software. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data, software, or related materials.


System Requirements

This DVD disc is readable on any computing platform that has standard DVD-R driver software installed. The minimum software requirements are a web browser, Acrobat Reader, and a text editor.


Project Summary

In October of 2001 and August of 2002, the U.S. Geological Survey conducted geophysical surveys of the Lower Atchafalaya River, the Mississippi River Delta, Barataria Bay, and the Gulf of Mexico south of East Timbalier Island, Louisiana. This report serves as an archive of unprocessed digital marine seismic reflection data, trackline maps, navigation files, observers' logbooks, GIS information, and formal FGDC metadata. In addition, a filtered and gained GIF image of each seismic profile is provided. Refer to the Acronyms page for expansion of acronyms and abbreviations used in this report.

The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry and others, 1975) and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU). Examples of SU processing scripts and in-house (USGS) software for viewing SEG-Y files (Zihlman, 1992) are also provided. Processed profile images, trackline maps, navigation files, and formal metadata may be viewed with a web browser. Scanned handwritten logbooks and Field Activity Collection System (FACS) logs may be viewed with Adobe Reader. Note: 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 data archived here were collected as part of the USGS River Contaminant Evaluation (RCE) Project. For further information about this study, refer to http://gulfsci.usgs.gov/missriv/index.html and Flocks and others (2002).

The USGS Florida Integrated Science Center (FISC) - Coastal and Watershed Studies in St. Petersburg, Florida, assigns a unique identifier to each cruise or field activity. For example, 01RCE05 indicates the data were collected in 2001 for the River Contaminant Evaluation (RCE) Project and the data were collected during the fifth field activity for that project in that calendar year. For a detailed description of the method used to assign the cruise ID, see http://walrus.wr.usgs.gov/infobank/programs/html/definition/activity.html or the formal metadata included in this report. The metadata also contains a detailed description of the method used to name each seismic line.

The boomer is an acoustic energy source that consists of capacitors charged to a high voltage and then discharged through a transducer towed on a sled at the sea surface. The chirp system uses a signal of continuously varying frequency. The sound source is a towfish typically flown 2-5 m above the seafloor. In both cases, the source emits a short acoustic pulse, or shot, that propagates through the water and sediment column. The acoustic energy is reflected at density boundaries (such as the seafloor or sediment layers beneath the seafloor), detected by the receiver, and recorded by a PC-based seismic acquisition system. This process is repeated at timed intervals (e.g., 0.5 s for boomer and 0.125 s for chirp) and recorded for specific intervals of time (e.g., 100 ms for boomer and 48 ms for chirp). In this way, a two-dimensional vertical image of the shallow geologic structure beneath the ship track is produced. Figure 1 shows boomer acquisition geometry, Figure 2 shows chirp acquisition geometry, and Table 1 displays acquisition parameters for both cruises. For more information about the acquisition equipment used, refer to the FACS equipment log for each cruise. Digital reproductions of all handwritten logbooks collected during each cruise are also provided.

The unprocessed seismic data were stored in SEG-Y format, (Barry and others, 1975). For a detailed description of the data format, refer to the SEG-Y Format page. See the How To Download SEG-Y Data page for more information about these files. Processed profiles can be viewed as GIF images from the Profiles page. Refer to the Software page for details about the processing and examples of the processing scripts.

Detailed information about the navigation systems used for each cruise can be found in Table 1 and the FACS equipment log for each cruise. To view the trackline maps and navigation files, and for more information about these items, see the Navigation page.

No data were collected for 01RCE05 lines 01b008-01b022 and 01c001-01c004. Digital data were not recorded for 01RCE05 lines 01c005-01c006 and 01c013-01c022. The original trace files for 01RCE05 lines 01c008-01c010 and 02RCE01 lines 02c07 and 02c09 were divided into two or more trace files (e.g., 01c008 became 01c008a and 01c008b) because the original total number of traces exceeded the maximum allowed by the processing system. No boomer data were collected during Cruise 02RCE01. Navigation is not available for 01RCE05 line 01c007, and navigation is intermittent for 02RCE01 line 02c09a. On the trackline maps, the location of missing navigation data within a line is inferred by linear interpolation of the first and last known data points and is represented by a blue line. Only the upper 40 ms of a total 48 ms of each 01RCE05 chirp profile and the upper 30 ms of a total 40 ms of each 02RCE01 chirp profile are displayed because little useful information was observed deeper in the sections.


DVD Organization

The Disc Contents page is a diagram of the location of all files and folders mentioned in the text and provides links to some of these files and folders.


Getting Started

To access the information contained on this disc, use a web browser to open the file index.htm located at the top level of the disc. This report is divided into five sections: Navigation Data and Maps, Seismic Profiles, Field Activity Logs, 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 only accessible if access to the Internet is available while viewing these documents.


Acknowledgments

Funding for this study was provided by the USGS Coastal and Marine Geology Program. We thank R/V G.K. Gilbert Captain Richard W. Young of the USGS in St. Petersburg, Florida, for his assistance in data collection. This document was improved by the reviews of Dale W. Griffin and Robert B. Halley of the USGS in St. Petersburg, Florida.


References Cited

Barry, R.M., Cavers, D.A., and Kneale, C.W., 1975, Recommended standards for digital tape formats: Geophysics, v. 40, p. 344-352. Also available online at: http://www.seg.org/publications/tech-stand.

Flocks, J.G., Kindinger, J.L., Ferina, N.F., Dreher, C.A., 2002, Sediment-hosted contaminants and distribution patterns in the Mississippi and Atchafalaya River deltas: Gulf Coast Association of Geological Societies Transactions, v. 52, p. 277-289.

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.


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