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

This CD-ROM document was produced in accordance with ISO 9660 CD-ROM standards and is readable on any computing platform that has standard CD-ROM driver software installed. Documentation 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 (e.g. Netscape or Internet Explorer). To access the information contained on this disc open the file index.html 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/). 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. Examples of SU processing scripts are provided in the boom.tar file located in the SEISUNIX subfolder in the SOFTWARE folder. 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. The processed boomer profiles, trackline maps, and logbooks (all GIF images) may also be viewed with your WWW browser.

This report consists of two-dimensional, marine, seismic reflection profile data from Crescent Beach Spring, Florida. These data were acquired April 26-27,1999 with the Research Vessel G.K. Gilbert. The data are available in a variety of formats, including binary, ASCII , HTML and GIF images. Binary data are in Society of Exploration Geophysicists (SEG) SEG-Y format and may be downloaded for further processing or display. 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.

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 subsurface structure of the spring, depths to various horizons and in assessing other submarine geologic characteristics and features near Crescent Beach Spring, Florida.

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 1 s 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 (Barry and others, 1975). 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 in this report are stored in SEG-Y, integer, Motorola format. The SEG-Y formatted trace data files are located in the SEGY folder 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: In order to comply with ISO 9660 naming standards tracklines d118_1806, d118_1812, and d118_1840 have been shortened to d1806, d1812, and d1840 respectively on the trackline maps, navigation files, and the SEG-Y data files. 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.

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 were 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, except for lines d118_1812 and d118_1840 which were recorded to 200 ms. The fire rate was every 0.5 sec which resulted in a shot spacing of about 1 m based on survey speeds of 3.5-4 knots.

GPS navigation was provided by a Trimble Centurian P-Code receiver directly fed to the acquisition system every second. The accuracy of this receiver is ±15 m. However, the SEG-Y format only allows for seconds of arc, which is equivalent to 31 m. The shotpoint navigation provided in this report has not been corrected to reflect the 20 m offset of the source to the GPS antenna. All the navigation data presented in this report are stored in flat ASCII text files. The raw navigation files which were extracted from the SEG-Y headers have not been edited and do not have the year or Julian Day written to the record. The raw navigation files are located in the RAWNAV subfolder of the NAV folder. The edited navigation provided in the EDITNAV subfolder of the NAV folder have been run through a filter and spurious fixes were removed, and the Julian Day and year have been added to them. The 500 shotpoint navigation has also been edited and the year and Julian Day have been added to the records. You can find the 500 shotpoint navigation in the SHOTNAV subfolder inside the NAV folder at the top level of the CD-ROM. These navigation files can be used to plot trackline maps of the seismic profiles at any scale or map projection desired. The trackline maps provided on this CD-ROM were created with ESRI's GIS software ArcView 3.2, exported to Adobe Illustrator and then saved as a GIF images. You may view these GIF images with your WWW browser, or the GIF images are located in the MAPS folder.

Also provided on this CD-ROM are Seismic Unix (SU) scripts that allow the user to strip off navigation fixes from the SEG-Y headers along with a fix for every 500th shot. The seismic data is then converted to SU format, filtered, gained and both Postscript and GIF formatted images are produced. These images can them be displayed using a variety of shareware programs such as ghostview (Unix, Linux, MAC, Windows), kview (Linux), or a web browser.

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 FDGC 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 trackline information in Microsoft Excel format.

HTML Folder: contains the necessary HTML files to allow the user access to the CD-ROM via any World Wide Web (WWW) browser.

IMAGES Folder: contains the 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, EDITNAV and SHOTNAV subfolders.

RAWNAV Subfolder: contains raw unedited navigation files in ASCII text format.

EDITNAV Subfolder: contains the edited navigation files in ASCII text format, with year and Julian Day added into each record.

SHOTNAV Subfolder: contains the navigation fixes for every 500th shotpoint interval extracted form the SEG-Y headers, in ASCII text format, with year and Julian Day added to each record.

SEGY Folder: contains the unprocessed, digital, boomer, single-channel, seismic reflection data for each trackline 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 (SU).

SOFTWARE Folder: Contains the SEISUNIX and USGS_EXE subfolders.

SEISUNIX Subfolder: Contains the Unix tar file (boom.tar) which contains example Seismic Unix (SU) 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.

This work was partially funded by the St. John's River Water Management District in Palatka, Fla. We thank Rich Young, captain of the R/V G.K. Gilbert for his help in the data collection; 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; Trent Faust and Rob Wertz, at the USGS in St. Petersburg, Fla. for their help with the web design and technical layout of the CD-ROM; and Gary Hill and Peter Swarzenski also with the USGS in St. Petersburg, Fla. for their editorial and technical reviews.

Barry, R.M., Cavers, D.A., and Kneale, C.W., 1975, Recommended standards for digital tape formats, Geophysics, v. 40, p. 344-352.

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 92-590.

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