Find U.S. Geological Survey Coastal and Marine Geology Program Web Information

READ-ME

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 CD-ROM archive, contact USGS Information at (888) ASK-USGS.

In June 1999, the U.S. Geological Survey, conducted a study to image the surficial and nearsurface features of the South Carolina coast, in the nearshore region between Little River Inlet to the entrance of Winyah Bay. The main objective of this cruise was to ascertain if erosion processes were occuring in this area. The data indicates that shallow seismic stratigraphic maps can be produced from a survey of the entire coast in order to further study the erosion processes. This CD-ROM serves as an archive of the unprocessed, digital, boomer seismic reflection data and all associated documentation and formal metadata. A filtered and gained GIF image of each seismic profile is also provided.

This CD-ROM (Compact Disc-Read Only Memory) document was produced in accordance with the ISO 9660 CD-ROM standards and is readable on any computing platform that has standard CD-ROM driver software installed. The documentation on this CD-ROM was produced using HyperText Markup Language (HTML) utilized by the World Wide Web (WWW) and allows the user to access the information by using a WWW browser (i.e. Netscape or Internet Explorer). To access the information contained on this disc open the file index.htm at the top-level of this disc with your WWW browser. This report also contains WWW links to USGS collaborators and other agencies. These links are only accessible if access to the Internet is also available while viewing the CD-ROM.

The archived boomer single-channel, seismic reflection data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry and others, 1975) and may be downloaded for processing with public domain software such as Seismic Unix (SU) (http://www.cwp.mines.edu/cwpcodes/). Examples of SU processing scripts are provided in the boom.tar file located in the SEISUNIX subfolder in the SOFTWARE folder at the top level of this CD-ROM. In-house (USGS) DOS and Microsoft Windows compatible software for viewing SEG-Y headers, DUMPSEGY.EXE (Zihlman, 1992) is provided in the USGS_EXE subfolder of the SOFTWARE folder located at the top level of the CD-ROM. The processed boomer profiles, reference maps, and logbooks (all GIF images) may also be viewed with your WWW browser.

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 CD-ROM archive, contact USGS Information at (888) ASK-USGS.

This report consists of two-dimensional marine seismic reflection profile data from the nearshore region of South Carolina between Little River Inlet to the entrance of Winyah Bay. These data were acquired in June of 1999, aboard the R/V G.K. Gilbert, and are available in a variety of formats, including binary, ASCII, HTML and GIF images. Binary data are stored in Society of Exploration Geophysicists (SEG) SEG-Y format and can be downloaded for further processing or display.

Purpose:
Marine seismic reflection data are used to image and map sedimentary and structural features of the seafloor and subsurface. These data are useful in mapping the extent and thickness of shallow sedimentary units along the coast of South Carolina, and in assessing other submarine geologic characteristics and features. The main objective of this cruise was to ascertain if these techniques could be used to study the erosional processes occurring between Little River Inlet to the entrance of Winyah Bay.

Supplemental Information:
Seismic reflection profiles are acquired by means of an acoustic source (usually generated electronically), and a hydrophone or hydrophone array. Both elements are typically towed in the water behind a survey vessel. The sound source emits a short acoustic pulse, which propagates through the water and sediment columns. The acoustic energy is reflected at density boundaries (such as the seafloor or sediment layers beneath the seafloor), and detected at the hydrophone. This process is repeated at intervals ranging between 100 ms and 1s depending on the source type. In this way a two-dimensional image of the geologic structure beneath the ship track is constructed.

Seismic data are stored in SEG-Y format, which is a standard digital format that can be read and manipulated by most seismic-processing software packages. The SEG-Y file format includes a 3200-byte descriptive header that should contain detailed information regarding the data acquisition and processing parameters. All data presented here are stored in SEG-Y, integer, Motorola format.The SEG-Y formatted trace data files are located in the SEGY folder at the top level of this disc and have a .tra extension. Additional recording parameters for each seismic data file can also be found in the .par file associated with each .tra file. However, the .par files and the trim_gga.pln file are only needed to replay the data with Triton Elics Delph Seismic software. WARNING: The acquisition system used to collect the seismic data presented in this report, may have added 6 ms to the top of each seismic trace. However, since no bathymetric data was simultaneously collected with the seismic data we have no way of proving that the added 6 ms does exist for this data set.

The seismic source employed here was a boomer transducer towed on a sled at the sea surface providing 100 joules per shot. The reflected energy was received by an Innovative Transducer Inc. (ITI) solid core streamer and recorded by PC-based Triton-Elics Delph Seismic acquisition software. The ITI streamer contains 10 hydrophones evenly spaced over 6 meters however only data received by elements 5-8 where summed, resulting in a higher signal to noise ratio for the data. The streamer was positioned parallel to the boomer sled and laterally separated from it by 7 m. The sled was towed 20 m behind the GPS antennae. The sample frequency of the data was 16000 Hz and the total record length was 100 ms. The fire rate was every 0.25

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 CD-ROM archive, contact USGS Information at (888) ASK-USGS.

GPS navigation was fed to the acquisition system every second by the R/V G.K. Gilbert's onboard navigation system, a Trimble Nav Graphic receiver. The accuracy of this receiver is within 100 m, however the data proved to be of poor quality and required extensive editing. A filter was designed to remove spurious data values and these edited results were used to generate the trackline maps provided on this CD-ROM. These maps were generated with ArcView 3.2 as geographic projections (no datum), and are provided here as GIF images. A position for every 500th shotpoint is also provided for easy registering of the data. All navigation files are stored as flat ASCII text files. The raw navigation files which did not have year or Julian day written to the recod are located in the RAWNAV subfolder of the NAV folder located at the top level of the CD-ROM. The edited navigation files, which have year and Julian day handwritten to each record are stored in the EDITNAV subfolder of the NAV folder, and the 500 shotpoint interval files are stored in the SHOTNAV subfolder of the NAV folder. These files also have year and Julian day handwritten into each record.

INDEX.HTM: The home page for viewing this report using a World Wide Web (WWW) browser.

README.TXT: A brief discription of this Open File Report in ASCII text format.

DISCLAIM.TXT: The ASCII text file stating the USGS disclaimer for this report.

METADATA.TXT: The formal FGDC metadata for the seismic data in ASCII text format.

FACS Folder: Contains the Field Activity Collection System sheets documenting the cruise overview, crew, equipment, and operation information in Microsoft Excel format.

HTML Folder: Contains the necessary HTML files to allow the user access to the CD-ROM via any WWW browser.

IMAGES Folder: Contains GIF images that are used by HTML hyperlinks.

LOGBOOKS Folder: Contains the scanned images of the handwritten observers logbooks as GIF images.

MAPS Folder: Contains the GIF images of the trackline maps.

NAV Folder: Contains the RAWNAV, SHOTNAV and EDITNAV subfolders.

RAWNAV Subfolder: Contains the raw, unedited DGPS navigation files in ASCII text format.

SHOTNAV Subfolder: Contains the navigation fixes for every 500th shotpoint interval extracted from the SEG-Y headers, in ASCII text format, with year and Julian day handwritten into each record.

EDITNAV Subfolder: Contains the edited DGPS navigation files in ASCII text format, with year and Julian day handwritten into each record.

SEGY Folder: Contains the unprocessed, digital, boomer, single-channel, seismic reflection data for the tracklines in SEG-Y format.

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 CD-ROM archive, contact USGS Information at (888) ASK-USGS.

SEISIMAG Folder: Contains the GIF images and thumbnails of the boomer seismic profiles generated with Seismic Unix.

SOFTWARE Folder: Contains the SEISUNIX and USGS_EXE subfolders.

SEISUNIX Subfolder: Contains the Unix tar file (boom.tar) which contains example Seismic Unix scripts used to process and plot the boomer reflection data and extract shot navigation from the SEG-Y headers.

USGS_EXE Subfolder: Contains the DOS program DUMPSEGY.EXE for viewing SEG-Y headers and the associated reference documentation.

This Compact Disc-Read Only Memory (CD-ROM) 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, make 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 necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. Any views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Although all data published on this CD-ROM 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.

We thank Rich Young with the USGS and Dave Bennett with Eckerd College, captains of the R/V G.K. Gilbert, for their help in the data collection; BJ Reynolds with the USGS, in St.Petersburg, Fla. for his contribution to the data collection process; Dave Foster and Jenna Hill, of the USGS Seafloor Mapping Group in Woods Hole, Mass. for providing examples of their archives; Jon Childs with the USGS, in Menlo Park, Calif. who provided examples of his formal metadata; Brock Murch and Bryan McCloskey at the USGS, in St.Petersburg, Fla. for their programming efforts in editing the navigation files; Shawn Dadisman at the USGS, in St.Petersburg, Fla. for her help with the content and layout; Trent Faust and Rob Wertz with the USGS in St.Petersburg for their help in the web design and technical layout of the CD-ROM; and Laura Moore and Jack Kindinger also both with the USGS in St.Petersburg, Fla. for their technical and editorial reviews.

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.

Back to Top of Page