James G. Flocks
Dana S. Wiese
Jake J. Fredericks
Arnell S. Forde
2016
<p>From August 11 to 31, 2014, the <abbr title="United States">U.S.</abbr> Geological Survey (<abbr title="U.S. Geological Survey">USGS</abbr>), in cooperation with the U.S. Fish and Wildlife Service (<abbr title="U.S. Fish and Wildlife Service">USFWS</abbr>), conducted a geophysical survey to investigate the geologic controls on barrier island framework and long-term sediment transport offshore of Breton Island, Louisiana as part of a broader <abbr title="U.S. Geological Survey">USGS</abbr> study on Barrier Island Mapping (<abbr title="Barrier Island Mapping">BIM</abbr>). Additional details related to this activity can be found by searching the USGS's Coastal and Marine Geoscience Data System (CMGDS), for field activity <a href="http://cmgds.marine.usgs.gov/fan_info.php?fan=2014-317-FA" target="_blank">2014-317-FA</a> (also known as 14BIM05). These surveys were funded through the <abbr title="U.S. Geological Survey">USGS</abbr> Coastal and Marine Geology Program (<abbr title="Coastal and Marine Geology Program">CMGP</abbr>) and the Louisiana Outer Coast Early Restoration Project. This report serves as an archive of unprocessed digital chirp subbottom data, trackline maps, navigation files, Geographic Information System (<abbr title="Geographic Information System">GIS</abbr>) files, Field Activity Collection System (<acronym title="Field Activity Collection System">FACS</acronym>) logs, and formal Federal Geographic Data Committee (<abbr title="Federal Geographic Data Committee">FGDC</abbr>) metadata. Gained digital images of the seismic profiles are also provided. Refer to the <a href="http://pubs.usgs.gov/ds/0972/html/ds972_abbreviations.html">Abbreviations</a> page for explanations of acronyms and abbreviations used in this report.</p>
<p>All chirp systems use an acoustic signal of continuously varying frequency; the EdgeTech 512i system used during this survey produced high-resolution, shallow-penetration (typically less than 50 milliseconds [<abbr title="millisecond">ms]</abbr>) profile images of sub-seafloor stratigraphy. The towfish contains a transducer that transmits and receives acoustic energy and typically is towed 1–2 meters (<abbr title="meters">m</abbr>) below the sea surface. As transmitted acoustic energy intersects density boundaries, such as the seafloor or sub-surface sediment layers, some energy is reflected back toward the transducer, received, and recorded by a Personal Computer (<abbr title="personal computer">PC)</abbr>-based seismic acquisition system. This process is repeated at regular intervals (for example, 0.125 seconds (<abbr title="seconds">s)</abbr>) and returned energy is recorded for a specific duration (for example, 50 <abbr title="milliseconds">ms</abbr>). In this way, a two-dimensional (<abbr title="Two-Dimensional">2-D</abbr>) vertical image of the shallow geologic structure beneath the ship's track is produced. <a href="http://pubs.usgs.gov/ds/0972/html/ds972_acquisition.html">Figure 2</a> displays the acquisition geometry. Refer to <a href="http://pubs.usgs.gov/ds/0972/html/ds972_table1.html">table 1</a> for a summary of acquisition parameters and <a href="http://pubs.usgs.gov/ds/0972/html/ds972_table2.html">table 2</a> for trackline statistics.</p>
<p>The archived trace data are in standard <a href="http://www.seg.org/resources/publications/misc/technical-standards" target="_blank"><acronym title="Society of Exploration Geophysicists">SEG</acronym> Y <abbr title="revision">rev.</abbr> 0</a> format (Barry and others, 1975); the first 3,200 bytes of the card image header are in American Standard Code for Information Interchange (<acronym title="American Standard Code for Information Interchange">ASCII</acronym>) format instead of Extended Binary Coded Decimal Interchange Code (<abbr title="Extended Binary Coded Decimal Interchange Code">EBCDIC</abbr>) format. The <acronym title="Society of Exploration Geophysicists">SEG</acronym> Y files are available on the <abbr title="Digital Versatile Disc">DVD</abbr> version of this report or online, downloadable via the <abbr title="United States Geological Survey">USGS</abbr> Coastal and Marine Geoscience Data System (<a href="http://cmgds.marine.usgs.gov/" target="blank">http://cmgds.marine.usgs.gov</a>). The data are also available for viewing using GeoMapApp (<a href="http://www.geomapapp.org/" target="blank">http://www.geomapapp.org</a>) and Virtual Ocean (<a href="http://www.virtualocean.org/" target="blank">http://www.virtualocean.org</a>) multi-platform open source software. <i>The Web version of this archive does not contain the <acronym title="Society of Exploration Geophysicists">SEG</acronym> Y trace files. To obtain the complete <abbr title="Digital Versatile Disc">DVD</abbr> archive, contact <abbr title="United States Geological Survey">USGS</abbr> Information Services at 1-888-ASK-USGS or infoservices@usgs.gov.</i> The <acronym title="Society of Exploration Geophysicists">SEG</acronym> Y files may be downloaded and processed with commercial or public domain software such as <a href="http://www.cwp.mines.edu/cwpcodes/index.html" target="_blank">Seismic Unix</a> (<abbr title="Seismic Unix">SU</abbr>) (Cohen and Stockwell, 2010). See the <a href="http://pubs.usgs.gov/ds/0972/html/ds972_download.html">How To Download <acronym title="Society of Exploration Geophysicists">SEG</acronym> Y Data</a> page for download instructions. The printable profiles are provided as Graphics Interchange Format (<acronym title="Graphics Interchange Format">GIF</acronym>) images processed and gained using <abbr title="Seismic Unix">SU</abbr> software and can be viewed from the<a href="http://pubs.usgs.gov/ds/0972/html/ds972_profiles.html">Profiles</a> page or by using the links located on the trackline maps; refer to the <a href="http://pubs.usgs.gov/ds/0972/html/ds972_software.html">Software</a> page for links to example <abbr title="Seismic Unix">SU</abbr> processing scripts.</p>
application/pdf
10.3133/ds972
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U.S. Geological Survey
Archive of Digital Chirp Subbottom Profile Data Collected During USGS Cruise 14BIM05 Offshore of Breton Island, Louisiana, August 2014
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