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 (888) ASK-USGS.

In June and July of 1996, the U.S. Geological Survey (USGS), in cooperation with Coastal Carolina University (CCU), conducted four nearshore geophysical surveys from southeast of Charleston Harbor to the mouth of the North Edisto River of South Carolina. This report serves as an archive of unprocessed digital seismic reflection data, trackline navigation files, trackline navigation maps, observers' logbooks, Geographic Information Systems (GIS) information, and formal Federal Geographic Data Committee (FGDC) metadata. In addition, a filtered and gained digital Graphics Interchange Format (GIF) image of each seismic profile is provided. For convenience, a list of acronyms and abbreviations frequently used in this report is also included.

This Digital Versatile Disc (DVD) document is readable on any computing platform that has standard DVD driver software installed. Documentation on this DVD was produced using Hyper Text Markup Language (HTML) utilized by the World Wide Web (WWW) and allows the user to access the information using a web browser (i.e. Netscape, Internet Explorer). To access the information contained on this disc, open the file 'index.htm' located at the top level of the disc using a web browser. This report also contains WWW links to USGS collaborators and other agencies. These links are only accessible if access to the Internet is available while viewing this DVD.

The archived boomer seismic reflection data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry et al., 1975) and may be downloaded for processing with public domain software such as Seismic Unix (SU), currently located at http://www.cwp.mines.edu/cwpcodes/index.html. 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 (888) ASK-USGS. Examples of SU processing scripts are provided in the BOOMLL.tar file located in the SU subfolder of the SOFTWARE folder located at the top level of this disc. In-house (USGS) DOS and Microsoft Windows compatible software for viewing SEG-Y headers—DUMPSEGY.EXE (Zihlman, 1992)—is provided in the USGS subfolder of the SOFTWARE folder. Processed profile images, trackline navigation maps, logbooks, and formal metadata may be viewed with a web browser.

ABSTRACT

This archive consists of marine seismic reflection profile data collected in four survey areas from southeast of Charleston Harbor to the mouth of the North Edisto River of South Carolina. These data were acquired June 26 - July 1, 1996, aboard the R/V G.K. Gilbert. Included here are data in a variety of formats including binary, American Standard Code for Information Interchange (ASCII), HTML, Portable Document Format (PDF), Rich Text Format (RTF), GIF and Joint Photographic Experts Group (JPEG) images, and shapefiles. Binary data are in Society of Exploration Geophysicists (SEG) SEG-Y format and may be downloaded for further processing or display. Reference maps and GIF images of the profiles may be viewed with a web browser. The GIS map documents provided were created with Environmental Systems Research Institute (ESRI) GIS software ArcView 3.2 and 8.1.

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 stratigraphy and in assessing other submarine geologic characteristics and features. These data were collected in cooperation with Coastal Carolina University as part of the USGS Coastal Change and Transport (CCT) Project.

SUPPLEMENTAL INFORMATION

The USGS Center for Coastal and Watershed Studies team in St. Petersburg, Florida, assigns a unique identifier to all seismic data collected during each cruise or field activity. The method used to assign the identifier for the activity is as follows: YYPPP##, where YY stands for the last 2 digits of the year in which the fieldwork is conducted, PPP is a 3-letter abbreviation for the project the data were collected for, and ## is a 2-digit event tag that represents a discreet leg or time period of fieldwork. Here, for example, 96CCT01 tells us the data were collected in 1996 for the Coastal Change and Transport Project and that the data were collected during the first field activity for that project in that calendar year.

Seismic reflection profiles are acquired by means of an acoustic source (usually generated electronically) and hydrophone or receiver arrays. Both elements are typically towed in the water behind a survey vessel. The sound 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) and detected at the receiver. This process is repeated at intervals ranging between 100 milliseconds (ms) and 1 second (s) depending on the seismic source employed. In this way, a two-dimensional vertical image of the geologic structure beneath the ship track is constructed.

The boomer energy source consists of capacitors that are charged to a high voltage and then discharged through a transducer in the water. The frequency range of the source is between 300 and 3,000 hertz (Hz). The transducer was towed on a sled at the sea surface providing 105 joules per shot. The reflected energy was received by an Innovative Technologies, Inc. (ITI) ST5 streamer and recorded by PC-based Triton Elics Delph Seismic acquisition software. The streamer contains 10 hydrophones, all of which were used. The phones are evenly spaced every 2 feet (0.6 m). The streamer was positioned parallel to the boomer sled and laterally separated from it by about 7 m. The sled was towed about 20 m behind the Global Positioning System (GPS) antenna, and no correction for this offset has been made. The sample frequency of the data was 12 kilohertz (kHz). All tracklines were recorded to 100 ms. Based on survey speeds of 3.5 - 4 knots and a shot rate of every 0.25 s, the shot spacing was about 0.5 m.

Seismic data were 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 3,200-byte descriptive header that contains 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 files have a .TRA extension. Additional recording parameters for each trace file can also be found in the .PAR file associated with each .TRA file. However, the .PAR and .PLN files included are only needed to process or display the data with Triton Elics Delph Seismic software. These files are all stored in the SEGY folder located at the top level of this disc. No SEG-Y data exists for tracklines SC696_12, SC696_13, SC696_14, SB629_19, and SB629_20. 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 (888) ASK-USGS.

GPS navigation was provided to the acquisition system approximately every 2 seconds by a Rockwell PLGR GPS receiver. The accuracy of this receiver is within about 15 m. The data required some editing to remove spurious data values. The edited results were used to generate the trackline maps presented here. The navigation data have not been corrected to reflect the 20 m offset between the shotpoint and the GPS antenna. Position fixes for every 500 shots and for the start of lines are also provided as an aid for registering of the data after plotting. All navigation files are stored as flat ASCII text files within the NAV folder located at the top level of this disc. Raw navigation files are stored in the RAWNAV subfolder, edited navigation files in the EDITNAV subfolder, and edited 500-shot interval files in the SHOTNAV subfolder.

The trackline maps provided in this archive are unprojected, set in geographic coordinates, World Geodetic System 1984 (WGS84). They were created using ESRI GIS software ArcView 3.2 and 8.1, exported to Adobe Illustrator for further editing, and saved for the web in JPEG format. These JPEG images are viewable with a web browser and can be found in the MAPS folder located at the top level of this disc. Also included on this disc are the ArcView map documents and shapefiles used to create the trackline maps presented here. The map documents are compatible with ArcGIS 8.x (Windows). The shapefiles can also be viewed using ArcView 3.x or public domain software ArcExplorer 2.0 (Windows) and 4.0 (Windows, Mac OSX, Unix, Linux), which can currently be downloaded from the ESRI website at http://www.esri.com/software/arcexplorer/index.html.

Field Activity Collection System (FACS) logs are available in both HTML and Rich Text Format. These can be found in the FACS folder located at the top level of this disc. Scanned versions of the handwritten logbooks are provided as PDF files which can be found in the LOGBOOKS folder located at the top level of this disc.

Also included on this disc are example Seismic Unix (SU) scripts that allow the user to strip off navigation fixes from the SEG-Y headers, along with a fix for every 500 shots, and produce a filtered and gained GIF image of each profile. These images can then be displayed using a variety of shareware programs such as ImageMagick (Unix, Linux) or a web browser. The example scripts are included in the BOOMLL.tar file which can be found in the SU subfolder of the SOFTWARE folder located at the top level of this disc.