Archive of Chirp Subbottom Profile Data Collected in 2018 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 2018 from the Northern Chandeleur Islands, Louisiana
Abstract:
From August 16 to 21, 2018, 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 2018-350-FA consisted of an EdgeTech SB-424 towfish running Discover version 4.09 acquisition software and towed on the port side of the research vessel (R/V) Sallenger, approximately 3.5 m opposite the global positioning system (GPS) reference point. The data were acquired using a frequency sweep of 4–20 kilohertz (kHz), a 43 kHz sample frequency, and recording length was approximately 40 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, 2018-350-FA_logs.zip.
  1. How might this data set be cited?
    Forde, Arnell S., DeWitt, Nancy T., Fredericks, Jake J., and Miselis, Jennifer L., 20191016, Archive of Chirp Subbottom Profile Data Collected in 2018 from the Northern Chandeleur Islands, Louisiana: U.S. Geological Survey Data Release doi:10.5066/P9U1WJXM, 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: -88.878178
    East_Bounding_Coordinate: -88.848386
    North_Bounding_Coordinate: 30.072008
    South_Bounding_Coordinate: 30.043875
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 16-Aug-2018
    Ending_Date: 21-Aug-2018
    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 0.0197884247. Longitudes are given to the nearest 0.0227369249. Latitude and longitude values are specified in Decimal Degrees. The horizontal datum used is WGS_1984.
      The ellipsoid used is WGS_84.
      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?
    2018-350-FA.txt, s2018-350-FA.txt, 2018-350-FA_s.txt
    These files, which are located in 2018-350-FA_nav.zip, represent the August 2018 seismic navigation data. The attributes described below are for the survey's shotpoint navigation file, 2018-350-FA.txt. For detailed information specific to the ArcGIS data, please see the associated shapefile metadata. (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:318965.462
    Maximum:321807.706
    Units:meters
    UTMY
    UTM-Y coordinate (Zone 16) (Source: Universal Transverse Mercator Coordinate System)
    Range of values
    Minimum:3325105.084
    Maximum:3328246.618
    Units:meters
    Line
    Trackline number (Source: U.S. Geological Survey) The naming convention used for each subbottom profile line is as follows: FAN_Line#, where 'FAN' is the USGS field activity number assigned to the survey (without the "-FA" suffix, for example, 2018-350), which is followed by an underscore, and 'Line#' is a 3-digit number representing a specific trackline. Trackline numbers range between 2018_350_001 and 2018_350_036.
    Shot
    Shotpoint number (Source: U.S. Geological Survey)
    Range of values
    Minimum:1
    Maximum:7248
    Lon
    Longitude (decimal degrees) (Source: World Geodetic System 1984 Geographic Coordinate System)
    Range of values
    Minimum:-88.878178
    Maximum:-88.848386
    Units:decimal degrees
    Lat
    Latitude (decimal degrees) (Source: World Geodetic System 1984 Geographic Coordinate System)
    Range of values
    Minimum:30.043875
    Maximum:30.072008
    Units:decimal degrees
    YEAR
    Year (Source: U.S. Geological Survey)
    Range of values
    Minimum:2018
    Maximum:2018
    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 6 to 51 MB. These data are included in the download file, 2018-350-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) data 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, 2018-350-FA_seisimag.zip.
    Entity_and_Attribute_Overview:
    Navigation file: Navigation files are available as ASCII text files. Provided are raw shotpoint navigation files for each line, reprojected survey shotpoint navigation, 1,000-shot-interval locations, and start of line files. The final navigation files are provided in 2018-350-FA_nav.zip.
    Entity_and_Attribute_Overview:
    GIS file: The GIS data associated with this survey are provided as a compressed zip file, 2018-350-FA_gis.zip, which is composed of an Esri map document, shapefiles, individual shapefile metadata, a Google Earth KMZ file, a folder for the processed profile images, and a readme file. 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 https://www.esri.com/en-us/arcgis/products/explorer-for-arcgis.
    Entity_and_Attribute_Detail_Citation:
    The entity and attribute information was 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 were provided by the USGS Coastal and Marine Geology Program. The authors thank Hunter Wilcox of Cherokee Nation Technologies for his assistance in data collection and piloting the R/V Sallenger. This document was improved by scientific/editorial and metadata reviews from Noreen Buster and Breanna Williams 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 2018-350-FA. Additional survey and data details are available from CMGDS at, https://cmgds.marine.usgs.gov/fan_info.php?fan=2018-350-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: 19-Aug-2019 (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: 19-Aug-2019 (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) 2018-350-FA.txt contains unique shotpoint positions (along each line) for the entire survey, (2) s2018-350-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) 2018-350-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:
    • 2018_350_001.txt-2018_350_031.txt; 2018_350_034.txt-2018_350_036.txt
    Data sources produced in this process:
    • 2018-350-FA.txt
    • s2018-350-FA.txt
    • 2018-350-FA_s.txt
    Date: 29-Aug-2018 (process 3 of 4)
    Trackline map creation: 2018-350-FA_location.mxd and associated shapefiles (.shp) were created with Esri ArcGIS 10.6 software. The survey navigation file, 2018-350-FA.txt, was imported into ArcMap 10.6.0.8321 and processed using the ArcScript "Points to Lines" to create a polyline shapefile of the cruise tracklines called 2018-350-FA_trkln. The 1,000-shot-interval and start-of-line files, s2018-350-FA.txt and 2018-350-FA_s.txt, were imported into ArcMap and saved as point shapefiles. A non-proprietary version of the location map was created by utilizing the ArcToolbox "Map to KML" tool, which converted each layer included in the .mxd document to keyhole markup language (.kml) format prior to them being compressed and saved as a .kmz file. The ArcGIS and Google Earth geospatial files provided in this data release are unprojected (geographic coordinates, WGS84). For detailed information about the ArcGIS files provided in this data release, please refer to the individual metadata records (*_metadata.txt and *.shp.xml) accompanying each shapefile and the readme file included in 2018-350-FA_gis.zip. 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:
    • 2018-350-FA.txt
    • s2018-350-FA.txt
    • 2018-350-FA_s.txt
    Data sources produced in this process:
    • 2018-350-FA_trkln.shp
    • 2018-350-FA_shots.shp
    • 2018-350-FA_sol.shp
    • 2018-350-FA.kmz
    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., 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:

    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 not show any major anomalies.
  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 a 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 2018 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 arcseconds every 1 second (s) and were subsequently converted to latitude and longitude coordinates (World Geodetic System of 1984, WGS84, realization G1762). The approximate 4-m offset between the chirp shot and ship's GPS reference point were 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 field activity. A chirp system malfunction occurred during the acquisition of line 2018-350_002; consequently, no navigation data were recorded for approximately three minutes (15:36:15 to 15:39:38). Since coordinate information was not saved to the SEG Y header for shots 3718-4627, those points have been removed from the associated navigation file (2018-350_002.txt). Due to time constraints and poor weather conditions, ofshore lines 2018-350_032 and 2018-350_033 were not 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 https://github.com/JohnWStockwellJr/SeisUnixindex.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/2018-350-FA_metadata.faq.html>
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