Tracklines of Chirp Seismic Lines 15 Through 27 for USGS Cruise GYRE 99002 (L15_27LN.SHP)

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Frequently anticipated questions:


What does this data set describe?

Title:
Tracklines of Chirp Seismic Lines 15 Through 27 for USGS Cruise GYRE 99002 (L15_27LN.SHP)
Abstract:
This GIS overlay is a component of the U.S. Geological Survey, Woods Hole Science Center's, Gulf of Mexico GIS database. The Gulf of Mexico GIS database is intended to organize and display USGS held data and provide on-line (WWW) access to the data and/or metadata.
A two week cruise aboard the R/V GYRE focused on mapping surficial sedimentary processes and their connection to the subsurface geology. The study area was on the upper continental slope in the northwestern Gulf of Mexico; an area of active hydrocarbon exploration. Active salt movement, hydrocarbon movement up faults, the presence of gas hydrates associated with biogenic and thermogenic methane, and overpressured sand deposits all present hazards to oil exploration in this area. This study used sidescan sonar and high-resolution chirp subbottom profiling techniques to map the surficial and shallow subsurface expression of these processes in two areas roughly 15 by 25 km in size. High-resolution multi-channel seismic-reflection data were collected simultaneously with the sidescan imagery to provide a link to the deeper subsurface. Additional multi-channel and Huntec seismic data were collected along regional lines between the detailed study areas to tie these studies to other areas of known hydrates and to wells where shallow overpressured sands have been drilled.
The detailed studies attempted to map entire geological systems in this upper slope environment to provide a broader perspective than can be seen from studying a single lease block. One study area focused on two adjacent salt withdrawal basins to assess the processes that are shaping the flanks of the basins, the processes affecting sedimentation in the basin floors, and to compare the deeper structures and surficial processes between the basins. The second study area focused on three salt domes, the processes associated with them, and how they affect the shallow subsurface stratigraphy. Initial observations suggest that most of the surface and shallow subsurface geohazards are associated with the flanks of salt structures. Here active salt movement generates faults along which hydrocarbons can escape to the seafloor, and tectonic oversteepenning generates slope failures.
  1. How might this data set be cited?
    Foster, David, 2005, Tracklines of Chirp Seismic Lines 15 Through 27 for USGS Cruise GYRE 99002 (L15_27LN.SHP): Open-File Report 2005-1071, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

    This is part of the following larger work.

    Twichell, D.C., Cross, V.A., Paskevich, V.F., Hutchinson, D.R., Winters, W.J., and Hart, P.E., 2005, GIS of selected geophysical and core data in the northern Gulf of Mexico continental slope collected by the U.S. Geological Survey: Open-File Report 2005-1071, U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details: 1 DVD-ROM
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -91.876524
    East_Bounding_Coordinate: -91.572242
    North_Bounding_Coordinate: 27.821626
    South_Bounding_Coordinate: 27.702160
  3. What does it look like?
    https://pubs.usgs.gov/of/2005/1071/data/seismic/1999/chirp/nav/l15_27ln-thumb.gif (GIF)
    Thumbnail image showing the extent and coverage of the data layer.
    https://pubs.usgs.gov/of/2005/1071/data/seismic/1999/chirp/nav/l15_27ln.gif (GIF)
    Overview image showing the extent and coverage of the data layer.
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 09-Apr-1999
    Ending_Date: 22-Apr-1999
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: vector digital data
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Vector data set. It contains the following vector data types (SDTS terminology):
      • String (26)
    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 0.000001. Longitudes are given to the nearest 0.000001. Latitude and longitude values are specified in Decimal degrees. The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257222.
  7. How does the data set describe geographic features?
    l15_27ln
    Shapefile Attribute Table (Source: ESRI)
    FID
    Internal feature number. (Source: ESRI) Sequential unique whole numbers that are automatically generated.
    Shape
    Feature geometry. (Source: ESRI) Coordinates defining the features.
    ID
    sequential numbers (Source: Software Computed)
    Range of values
    Minimum:1
    Maximum:26
    Units:integer count
    Resolution:1
    ATTRIBUTE
    Line and file numbers associated with each survey line (Source: USGS) Character String containing the number and character string defining each track line.
    IMAGE
    Path and image of seismic profile associated with each line. (Source: USGS) Character string giving the relative path and name of the seismic image associated with this line.
    LENGTH
    Length of trackline (Source: USGS)
    Range of values
    Minimum:4617.285
    Maximum:20881.074
    Units:meters
    Resolution:.001

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • David Foster
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    David Foster
    U.S. Geological Survey
    Geologist
    384 Woods Hole Road
    Woods Hole, MA
    USA

    (508) 548-8700 x2271 (voice)
    (508) 457-2310 (FAX)
    dfoster@usgs.gov

Why was the data set created?

This GIS data layer shows the tracklines along which SIS-1000 chirp subbottom profile data and sidescan sonar data were collected in the Gulf of Mexico during a cruise aboard the R/V GYRE (USGS cruise 99002) to study the shallow subsurface geology of an area of possible gas hydrate occurrence. The navigation has been corrected to show the SIS-1000 vehicle location rather than the ship location (Foster and others, 2000). This survey was on the upper continental slope offshore of Louisiana, and chirp profiles were collected along 339 km of tracklines.

How was the data set created?

  1. From what previous works were the data drawn?
    Information unavailable from original metadata. (source 1 of 1)
    Foster, D.S., Twichell, D.C., Danforth, W.W., Irwin, B.J., Nichols, D.R., and O'Brien, T.F., 1999, Archive of SIS-1000 CHIRP subbottom data, collected during USGS cruise GYRE 99002 Gulf of Mexico, 9-22 April, 1999: Open-File Report 99-586, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Science Center, Woods Hole, MA.

    Online Links:

    Type_of_Source_Media: CD-ROM
    Source_Contribution: Shapefile copied from the publication
  2. How were the data generated, processed, and modified?
    Date: unknown (process 1 of 7)
    GPS navigation for the ship and slant-range distances between the ship and the vehicle (when they were available) were logged to disk in the field Person who carried out this activity:
    David Foster
    U.S. Geological Survey
    Geologist
    384 Woods Hole Road
    Woods Hole, MA
    USA

    (508) 548-8700 x2271 (voice)
    (508) 457-2310 (FAX)
    dfoster@usgs.gov
    Data sources used in this process:
    • DGPS receiver
    Data sources produced in this process:
    • 99_099.txt - 99_111.txt
    Date: unknown (process 2 of 7)
    An acoustic transponder was used to determine range from the ship to the sonar fish; however this system did not always function, particularly in deeper water. Slant range and sonar fish depth below the sea surface were used to calculate the layback distance (horizontal offset) between the ship and sonar fish. The fish was assumed to be directly behind the ship, given the azimuth of the ships track. Different methods were used to calculate or estimate the layback distance for different lines.
    Lines 15 and 16 of Mosaic Area Two do not have acoustic ranging data available. The SEG-Y file headers contain ship position (UTM zone 15). The ASCII shotpoint navigation files contain geographic coordinates for sonar fish position obtained by comparing fish depth and layback distance from lines 17 and 18 where acoustic slant ranges were good. Because lines 15 and 16 are in relatively shallow water and fish depths did not exceed 300 meters, this method of estimating layback is reasonable. Based on the layback verses fish depth analysis of lines 15 and 16, the horizontal errors may be as much as 50 meters. Layback depends on other variables other than fish depth. Ship speed was not considered in the analysis.
    Lines 17 and 18 of Mosaic Area Two were determined to have good acoustic slant range, thus the calculated layback was used to obtain sonar fish position. The ASCII shotpoint contain geographic coordinates for sonar fish position as well as ship position. The SEG-Y file headers contain ship position (UTM zone 15).
    Lines 19-27 of Mosaic Area Two had unreliable slant range information due to the length of fish layback and deeper water. Laybacks were estimated for lines 19 and 20 based on the analysis of fish depth and layback in lines 17 and 18, but when fish depths exceeded 300 meters the error in this method increases. Instead another method of comparing water depth from the sonar fish (fish depth and altitude combined) to NOAA gridded Seabeam bathymetry. Offsets between the bathymetry and the water depth from the fish showed the apparent layback for each line. Using this method, the layback was estimated and the corrected navigation compared to the gridded bathymetry. This showed good correlation between water depths and sea floor features. Furthermore, the estimated layback was used to navigate the sidescan sonar data in the mosaicking process, and features on adjacent sidescan sonar lines matched well. The ASCII navigation files contain ship position as well as layback positions. The SEG-Y file headers contain ship position (UTM zone 15).
    The processing was done by David Foster, and is summarized in Foster and others (2000) Person who carried out this activity:
    David Foster
    U.S. Geological Survey
    Geologist
    384 Woods Hole Road
    Woods Hole, MA
    USA

    (508) 548-8700 x2271 (voice)
    (508) 457-2310 (FAX)
    dfoster@usgs.gov
    Date: unknown (process 3 of 7)
    The navigation text file was imported to ArcView and converted to a shapefile. Person who carried out this activity:
    David Foster
    U.S. Geological Survey
    Geologist
    384 Woods Hole Road
    Woods Hole, MA
    USA

    508-548-8700 x 2271 (voice)
    508-457-2310 (FAX)
    dfoster@usgs.gov
    Data sources produced in this process:
    • l15_27ln.shp
    Date: 07-Mar-2017 (process 4 of 7)
    Edits to the metadata were made to fix any errors that MP v 2.9.36 flagged. This is necessary to enable the metadata to be successfully harvested for various data catalogs. In some cases, this meant adding text "Information unavailable" or "Information unavailable from original metadata" for those required fields that were left blank. Other minor edits were probably performed (title, publisher, publication place, etc.). Attempted to modify http to https where appropriate. The link to the larger work citation had to be fixed. The links to the browse graphics had to be fixed. An online link was added to the cross-reference. The source information was incomplete and had to be modified to meet the standard. The metadata date (but not the metadata creator) was edited to reflect the date of these changes. The metadata available from a harvester may supersede metadata bundled within a download file. Compare the metadata dates to determine which metadata file is most recent. 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
    Date: 20-Jul-2018 (process 5 of 7)
    USGS Thesaurus keywords added to the keyword section. 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
    Date: 18-Nov-2019 (process 6 of 7)
    Crossref DOI link was added as the first link in the metadata. 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
    Date: 08-Sep-2020 (process 7 of 7)
    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?
    Foster, D.F., Twichell, D.C., Danforth, W.W., Irwin, B.J., Nichols, D.R., and O'Brien, T.F., 2000, Archive of SIS-1000 CHIRP subbottom data collected during USGS cruise GYRE 99002 Gulf of Mexico, 9-22 April, 1999: Open-File Report 99-586, U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details: 3 CD-ROMS

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

  1. How well have the observations been checked?
  2. How accurate are the geographic locations?
    The ship was navigated with differential GPS, and location of the deep-towed sidescan vehicle was calculated in a variety of ways. In shallow water an acoustic ranging system was used in concert with vehicle depth and ship heading to compute vehicle location. In deeper water depths where the acoustic ranging system did not work, vehicle location was calculated in one of two ways. In some places the amount of wire out was used in place of the acoustic range. In other places, vehicle location was calculated by measuring the offset between features observed on the NOAA multibeam bathymetry and the tow vehicle echo sounder. This offset was measured at several points along each track and was used to compute vehicle navigation. Vehicle location was interpolated between the measured points. Comparison of features on the surface-towed seismic data with the same features on the deep-towed seismic data indicates that the offset mostly is less than 100 m.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    Information unavailable from original metadata.
  5. How consistent are the relationships among the observations, including topology?
    No additional checks for topological consistency were performed on the data. No duplicate features are present.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: None
Use_Constraints:
Public domain data from the U.S. government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey (USGS) as the source of this information.
  1. Who distributes the data set? (Distributor 1 of 1)
    David Twichell
    U.S. Geological Survey
    Oceanographer
    384 Woods Hole Road
    Woods Hole, MA
    USA

    (508) 548-8700 x2266 (voice)
    (508) 457-2310 (FAX)
    dtwichell@usgs.gov
  2. What's the catalog number I need to order this data set? Downloadable Data
  3. What legal disclaimers am I supposed to read?
    Although this data set has been used by the U.S. Geological Survey (USGS), no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and/or related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials.
    Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
  4. How can I download or order the data?
    • Availability in digital form:
      Data format: The SHP file contains the geospatial data. The SHX file contains the index of the geospatial data. The DBF file contains the attribute data in dBase format. The PRJ file contains the coordinate system information (optional). The AVL file contains the legend information (optional). The SBN and SBX files contain the spatial index of the geospatial data (optional). The XML file contains the metadata describing the data set <data set name>.shp.xml. An ASCII version of the metadata file. A browse graphic showing the data layer coverage and extent (optional). in format SHP (version 3.3) ESRI polyline shapefile Size: 0.047
      Network links: https://pubs.usgs.gov/of/2005/1071/data/seismic/1999/chirp/nav/l15_27ln.zip
      Media you can order: DVD-ROM (Density 4.75 Gbytes) (format UDF)
    • Cost to order the data: None

  5. What hardware or software do I need in order to use the data set?
    The data are available in Environmental Systems Research Institute (ESRI) shapefile format. The user must have ArcGIS® or ArcView® 3.0 or greater software to read and process the data file. In lieu of ArcView or ArcGIS, the user may utilize another GIS application package capable of importing data. A free data viewer, arcexplorer, capable of displaying the data is available from ESRI at www.esri.com.

Who wrote the metadata?

Dates:
Last modified: 08-Sep-2020
Metadata author:
Dave Foster
U.S. Geological Survey
Seafloor Mapping Group
384 Woods Hole Road
Woods Hole, MA
USA

(508) 548-8700 x2271 (voice)
(508) 457-2310 (FAX)
dfoster@usgs.gov
Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)

This page is <https://cmgds.marine.usgs.gov/catalog/whcmsc/open_file_report/ofr2005-1071/l15_27lnmeta.faq.html>
Generated by mp version 2.9.50 on Tue Sep 21 18:20:20 2021