Archive of Chirp Subbottom Profile Data Collected in 2017 From the Northern Chandeleur Islands, Louisiana

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Frequently anticipated questions:

What does this data set describe?

Title:
Archive of Chirp Subbottom Profile Data Collected in 2017 From the Northern Chandeleur Islands, Louisiana
Abstract:
From August 7 to 16, 2017, the U.S. Geological Survey (USGS) conducted a geophysical survey to investigate the geologic controls on barrier island evolution and medium-term and interannual sediment transport along the sand berm constructed in 2011 (offshore, at the northern end of the Chandeleur Islands, Louisiana) as mitigation of the Deepwater Horizon oil spill. This investigation is part of a broader USGS project, which seeks to better understand barrier island evolution over medium time scales (months to years). This publication serves as an archive of unprocessed, digital chirp subbottom data, survey trackline map, navigation files, geographic information system (GIS) data, and formal Federal Geographic Data Committee (FGDC) metadata. Processed subbottom profile images are also provided. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG Y revision 0 format (Barry and others, 1975) and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU). These data are available for viewing using GeoMapApp (http://www.geomapapp.org/) and Virtual Ocean (http://www.virtualocean.org/) multi-platform open source software. In addition, the SEG Y files can be downloaded from the USGS Coastal and Marine Geoscience Data System (CMGDS, https://cmgds.marine.usgs.gov).
Supplemental_Information:
All Chirp systems use a signal of continuously varying frequency; the system used during this survey produces high-resolution, shallow-penetration (typically less than 75-milliseconds [ms]) profile images of sub-seafloor stratigraphy. The towfish contains a transducer that transmits and receives acoustic energy and is typically towed 1-2 meters (m) below the sea's surface. As transmitted acoustic energy intersects density boundaries, such as the seafloor or sub-surface sediment layers, energy is reflected toward the transducer, received, and recorded by a PC-based seismic acquisition system. This process is repeated at regular intervals (for example, 0.125 seconds [s]) and returned energy is recorded for a specific duration (for example, 50 ms). In this way, a two-dimensional (2D) vertical image of the shallow geologic structure beneath the towfish is produced. The seismic source utilized during 2017-337-FA consisted of an EdgeTech SB-424 towfish running Discover version 4.09 acquisition software, towed on the port side of the R/V Sallenger, approximately 3.5 m opposite the global positioning system (GPS) reference point. The data were acquired using a frequency sweep of 4-24 kilohertz (kHz), a 43 kHz sample frequency, and recording length was approximately 66.5 ms. Based on survey speeds of 3.5-4.5 knots, the shot spacing was approximately 0.450 m. The binary portion of the unprocessed seismic data is stored in SEG Y rev. 0, IBM float format, which is a standard digital format that can be read and manipulated by most seismic processing software packages; the first 3,200 bytes of the file header are in American Standard Code for Information Interchange (ASCII) format instead of Extended Binary Coded Decimal Interchange Code (EBCDIC) format. The SEG Y formatted trace files have a .sgy extension and may be downloaded and processed with commercial or public domain software such as Seismic Unix (Cohen and Stockwell, 2010). The printable profiles provided are chirp subbottom profile images that were processed using SU software. Survey Field Activity Collection System (FACS) and geophysical logs are also provided as supplemental information in the download file, 2017-337-FA_logs.zip.
  1. How might this data set be cited?
    Forde, Arnell S., DeWitt, Nancy T., Fredericks, Jake J., and Miselis, Jennifer L., 20181106, Archive of Chirp Subbottom Profile Data Collected in 2017 From the Northern Chandeleur Islands, Louisiana: U.S. Geological Survey Data Release doi:10.5066/P9E8VRGO, U.S. Geological Survey - St. Petersburg Coastal and Marine Science Center, St. Petersburg, Florida.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -88.878025
    East_Bounding_Coordinate: -88.850142
    North_Bounding_Coordinate: 30.072017
    South_Bounding_Coordinate: 30.044906
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 07-Aug-2017
    Ending_Date: 16-Aug-2017
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: multimedia presentation
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Point data set.
    2. What coordinate system is used to represent geographic features?
      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.0197884765. Longitudes are given to the nearest 0.0227336944. Latitude and longitude values are specified in Decimal Degrees. The horizontal datum used is World Geodetic System of 1984.
      The ellipsoid used is WGS 1984.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257223563.
  7. How does the data set describe geographic features?
    2017-337-FA.txt, s2017-337-FA.txt, 2017-337-FA_s.txt
    Shotpoint navigation files (Source: SEG Y headers, https://seg.org/Publications/tech-stand.)
    UTMX
    UTM-X coordinate (Zone 16) (Source: Universal Transverse Mercator Coordinate System)
    Range of values
    Minimum:318979.671
    Maximum:321636.88
    Units:meters
    UTMY
    UTM-Y coordinate (Zone 16) (Source: Universal Transverse Mercator Coordinate System)
    Range of values
    Minimum:3325218.753
    Maximum:3328246.93
    Units:meters
    Line
    Trackline number (Source: U.S. Geological Survey) The naming convention used for each subbottom line is as follows: Lxy, where 'L' is an abbreviation of line and precedes the line number, 'x' is a 2-digit number representing a specific trackline number, and 'y' is a letter (in this case, b) representing a new line if recording was prematurely terminated or reran for quality or acquisition problems. If a trackline exceeded the file size limit/maximum shotpoint number (as determined by the acquisition software, Discover v. 4.09) the filename was appended with sequentially increasing numbers such as .001, .002, etc. A single line, JD221_line14, did not use the previously described naming convention.
    Shot
    Shotpoint number (Source: U.S. Geological Survey)
    Range of values
    Minimum:1
    Maximum:7291
    Lon
    Longitude (decimal degrees) (Source: World Geodetic System 1984 Geographic Coordinate System)
    Range of values
    Minimum:-88.878025
    Maximum:-88.850142
    Units:decimal degrees
    Lat
    Latitude (decimal degrees) (Source: World Geodetic System 1984 Geographic Coordinate System)
    Range of values
    Minimum:30.044906
    Maximum:30.072017
    Units:decimal degrees
    YEAR
    Year (Source: U.S. Geological Survey)
    Range of values
    Minimum:2017
    Maximum:2017
    DOY:HR:MIN:SEC
    Day of year:hour:minute:second (Source: U.S. Geological Survey) Day of year, hour, minute and second of data acquisition
    Entity_and_Attribute_Overview:
    Binary data file: Seismic trace data are available as binary files in SEG Y format. These files have a .sgy extension and range in size from 19.3 to 86.1 MB. These data are included in the download file, 2017-337-FA_segy.zip, and can also be found by going to https://cmgds.marine.usgs.gov. The SEG Y rev. 0 format (Barry and others, 1975) presented here consists of the following: a 3,600-byte reel identification header, with the first 3,200 bytes consisting of an ASCII header block followed by a 400-byte binary header block, both of which include information specific to line and reel number; a trace data block that follows the reel identification header, with the first 240 bytes of each trace block consisting of the binary trace identification header; and seismic data samples that follow the trace identification header.
    Entity_and_Attribute_Overview:
    Graphic image file: Printable versions of the processed subbottom profiles are available as GIF images and are included in the download file, 2017-337-FA_seisimag.zip.
    Entity_and_Attribute_Overview:
    Navigation file: Navigation files are available as ASCII text files. Provided are raw shotpoint navigation files, reprojected survey shotpoint navigation, 1,000-shot-interval locations, and start of line files. The final navigation files are provided in 2017-337-FA_nav.zip.
    Entity_and_Attribute_Overview:
    GIS file: The GIS data associated with this survey are provided as a compressed zip file, 2017-337-FA_arc.zip, which is composed of an Esri map document, shapefiles, a folder for the processed profile images, shapefile metadata for each GIS file and a readme document. The shapefiles provided may also be viewed using other versions of Esri desktop software including their free software Explorer for ArcGIS, which is available at http://www.esri.com/software/arcgis/explorer/index.html.
    Entity_and_Attribute_Detail_Citation:
    The entity and attribute information were generated by the individual and/or agency identified as the originator of the dataset. Please review the rest of the metadata record for additional details and information.

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Arnell S. Forde
    • Nancy T. DeWitt
    • Jake J. Fredericks
    • Jennifer L. Miselis
  2. Who also contributed to the data set?
    Funding and (or) support for this study was provided by the USGS Coastal and Marine Geology Program. The authors thank Andy Farmer of Cherokee Nation Technologies for his assistance in data collection and piloting the research vessel (R/V) Sallenger. This document was improved by reviews from Stephen Bosse and Chelsea Stalk of the USGS - St. Petersburg, Florida.
  3. To whom should users address questions about the data?
    Arnell S. Forde
    U.S. Geological Survey
    Geologist
    600 4th Street South
    Saint Petersburg, FL
    USA

    (727) 502-8000 (voice)
    aforde@usgs.gov

Why was the data set created?

To archive all digital chirp subbottom profile data and associated files collected during Field Activity Number 2017-337-FA. Additional survey and data details are available from CMGDS at, https://cmgds.marine.usgs.gov/fan_info.php?fan=2017-337-FA.

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: 08-Aug-2018 (process 1 of 4)
    Chirp processing: The SEG Y data were processed with Seismic Unix (Release 44) software to produce gained Graphics Interchange Format (GIF) images of the subbottom profiles included in this data release. A representative chirp data processing sequence consisted of (1) removing navigation data for each shot and converting the SEG Y file to SU format, (2) applying automatic gain control, (3) generating a PostScript image of the traces, and (4) converting the PostScript image to a GIF image. For additional SU processing and script details, please refer to Data Series 1077 (Forde and others, 2018). Person who carried out this activity:
    Arnell S. Forde
    U.S. Geological Survey
    Geologist
    600 4th Street South
    St. Petersburg, FL

    (727) 502-8000 (voice)
    aforde@usgs.gov
    Data sources used in this process:
    • SEG Y
    Data sources produced in this process:
    • SEG Y.gif
    Date: 08-Aug-2018 (process 2 of 4)
    Navigation processing: Location data were extracted from the SEG Y headers using Seismic Unix software and output as ASCII text files; PROJ.5.1.0 (https://proj4.org/) software was used to project WGS84 latitude and longitude coordinates to Universal Transverse Mercator (UTM) northings and eastings (WGS84, Zone 16, meters). Raw navigation files for each seismic line, saved by line number, were concatenated into comma-delimited text files for use with Esri ArcGIS software. The final output files are as follows: (1) 2017-337-FA.txt contains unique shotpoint positions (along each line) for the entire survey, (2) s2017-337-FA.txt includes the 1,000-shot-interval locations that were generated to correlate shot locations on the trackline map with evenly spaced 1,000-shot index markers along the top of the printable profile images, and (3) 2017-337-FA_s has the start-of-line locations for each trackline. The concatenated, comma-delimited text files were later imported into ArcGIS and saved as either a point or polyline file (in Esri's shapefile format) for use in the map document (.mxd) included in this archive. Person who carried out this activity:
    Arnell S. Forde
    U.S. Geological Survey
    Geologist
    600 4th Street South
    St. Petersburg, FL

    (727) 502-8000 (voice)
    aforde@usgs.gov
    Data sources used in this process:
    • L01-36.txt and JD221_line14.txt
    Data sources produced in this process:
    • 2017-337-FA.txt
    • s2017-337-FA.txt
    • 2017-337-FA_s.txt
    Date: 2017 (process 3 of 4)
    Trackline map creation: 2017-337-FA_location.mxd was created with Esri ArcGIS 10.3.1 software. The survey navigation file, 2017-337-FA.txt, was imported into ArcMap 10.3.1 and processed using the ArcScript "Points to Lines" to create a line shapefile of the cruise tracklines called 2017-337-FA_trkln. The 1,000-shot-interval file and the start-of-line file were imported into ArcMap and saved as point shapefiles 2017-337-FA_shots and 2017-337-FA_sol, respectively. The ArcGIS files included in this release are unprojected (geographic coordinates, WGS84). Please refer to the individual shapefile metadata and readme file, included in 2017-337-FA_arc.zip, for detailed information about the geospatial files provided in this data release. Person who carried out this activity:
    Arnell S. Forde
    U.S. Geological Survey
    Geologist
    600 4th Street South
    St. Petersburg, FL

    (727) 502-8000 (voice)
    aforde@usgs.gov
    Data sources used in this process:
    • 2017-337-FA.txt
    • s2017-337-FA.txt
    • 2017-337-FA_s.txt
    Data sources produced in this process:
    • 2017-337-FA_trkln.shp
    • 2017-337-FA_shots.shp
    • 2017-337-FA_sol.shp
    Date: 13-Oct-2020 (process 4 of 4)
    Added keywords section with USGS persistent identifier as theme keyword. Person who carried out this activity:
    U.S. Geological Survey
    Attn: VeeAnn A. Cross
    Marine Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2251 (voice)
    508-457-2310 (FAX)
    vatnipp@usgs.gov
  3. What similar or related data should the user be aware of?
    Barry, K.M., Cavers, D.A., and Kneale, C.W., 1975, Recommended standards for digital tape formats: Geophysics v. 40, no. 2.

    Online Links:

    Other_Citation_Details: pages 344-352
    Cohen, J.K., and Stockwell, J.W., Jr., CWP/SU, 2010, Seismic Un*x Release No. 44: An open source software package for seismic research and processing: Center for Wave Phenomena, Colorado School of Mines, Golden, Colorado.

    Online Links:

    Forde, Arnell S., DeWitt, Nancy T., and Miselis, Jennifer L., 20181031, Archive of Chirp Subbottom Profile Data Collected in 2016 from the Northern Chandeleur Islands, Louisiana: U.S. Geological Survey Data Release doi:10.5066/P9NFK0K4, U.S. Geological Survey - St. Petersburg Coastal and Marine Science Center, St. Petersburg, Florida.

    Online Links:

    Forde, Arnell S., DeWitt, Nancy T., Fredericks, Jake J., and Miselis, Jennifer L., 20180116, Archive of Chirp Subbottom Profile Data Collected in 2015 from the Northern Chandeleur Islands, Louisiana: U.S. Geological Survey Data Release doi:10.5066/F7668C5C, U.S. Geological Survey - St. Petersburg Coastal and Marine Science Center, St. Petersburg, Florida.

    Online Links:

    Forde, Arnell S., DeWitt, Nancy T., Fredericks, Jake J., and Miselis, Jennifer L., 20180117, Chirp Subbottom Profile Data Collected in 2015 from the Northern Chandeleur Islands, Louisiana: U.S. Geological Survey Data Series 1077, U.S. Geological Survey, Reston, Virginia.

    Online Links:

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
    The validity or accuracy of marine subbottom profiles is highly qualitative and dependent on equipment and operating condition variables. Visual inspection of the images rendered from the data did show the presence of some anomalies, at depth, within the nearshore lines. The cause for this issue was likely due to mechanical interference from a concurrently running piece of equipment.
  2. How accurate are the geographic locations?
    An Applanix POS MV Wavemaster II system was used to provide position information. Manufacture stated accuracy for positioning utilizing differential global positioning system (DGPS) is 0.5-2 m. To ensure consistent spacing between survey lines (for example, 5 m in the nearshore and 10 m for offshore lines), pre-determined trackline locations were imported into HYPACK 2016a navigation software and followed during seismic data collection. Positions from the POS MV inertial aided navigation system (IANS) were recorded and written to seismic trace headers in latitude and longitude coordinates (World Geodetic System of 1984, WGS84, realization G1762) every 1 second (s). The approximate 4-m offset between the chirp shot and ship's GPS reference point was not accounted for during acquisition, nor have the ASCII navigation files and trackline map been corrected to reflect the offset.
  3. How accurate are the heights or depths?
    These data are not to be used for bathymetry. Two-way travel (TWT) times shown on the printable profile images are relative to the chirp towfish position, not to the sea surface.
  4. Where are the gaps in the data? What is missing?
    A total of 34 seismic lines were collected during this survey.
  5. How consistent are the relationships among the observations, including topology?
    These datasets are from one field activity with consistent instrument calibrations.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: None. These data are held in the public domain.
Use_Constraints:
Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. The U.S. Geological Survey requests to be acknowledged as originator of the data in future products or derivative research.
  1. Who distributes the data set? (Distributor 1 of 1)
    Arnell S. Forde
    U.S. Geological Survey
    Geologist
    600 4th Street South
    St. Petersburg, FL
    USA

    (727) 502-8000 (voice)
    aforde@usgs.gov
    Contact_Instructions:
    The SEG Y files included in this data release are also downloadable from the Coastal and Marine Geoscience Data System https://cmgds.marine.usgs.gov.
  2. What's the catalog number I need to order this data set?
  3. What legal disclaimers am I supposed to read?
    This publication was prepared by an agency of the United States Government. Although these data were processed successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied is made regarding the display or utility of the data on any other system, nor shall the act of distribution imply any such warranty. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the data described and (or) contained herein. Reference herein 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.
  4. How can I download or order the data?
  5. What hardware or software do I need in order to use the data set?
    Use of SEG Y data requires specialized seismic processing software, such as public domain software Seismic Unix http://www.cwp.mines.edu/cwpcodes/index.html.

Who wrote the metadata?

Dates:
Last modified: 13-Oct-2020
Metadata author:
Arnell S. Forde
U.S. Geological Survey
Geologist
600 4th Street South
St. Petersburg, FL
USA

(727) 502-8000 (voice)
aforde@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/spcmsc/2017-337-FA_metadata.faq.html>
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