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U.S. Geological Survey
Open-File Report 2005-1411

High-resolution multichannel seismic-reflection data acquired in the northern Gulf of Mexico, 2003

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What does this data set describe?

Title:
High-resolution multichannel seismic-reflection data acquired in the northern Gulf of Mexico, 2003
Abstract:
This report consists of two-dimensional marine seismic reflection profile data from the northern Gulf of Mexico. These data were acquired in 2003 with the Research Vessel Gyre (G-1-03-GM). The data are available in binary and JPEG image formats. Binary data are in Society of Exploration Geologists (SEG) SEG-Y format and may be downloaded for further processing or display. Reference maps and JPEG images of the profiles may be viewed with your Web browser.
Supplemental_Information:
Multichannel seismic reflection profiles are acquired by means of an acoustic source (usually compressed air discharged via an air gun or water gun), and a 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. As the vessel moves, this process is repeated at intervals ranging between 10 and 30 meters depending on the source type. In this way a two-dimensional image of the geologic structure beneath the ship track is constructed. Additional information about the USGS survey G-1-03-GM is available at <http://pubs.usgs.gov/of/2003/of03-474/>. The data window for G-1-03-GM is -94.818 26.715 -89.239 29.345 (decimal degrees).
  1. How should this data set be cited?

    Hart, Patrick E. , Hutchinson, Deborah R. , and Lee, Myung, 2005, High-resolution multichannel seismic-reflection data acquired in the northern Gulf of Mexico, 2003: U.S. Geological Survey Open-File Report 05-1411, U.S. Geological Survey, Menlo Park, CA.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -94.82
    East_Bounding_Coordinate: -89.24
    North_Bounding_Coordinate: +29.35
    South_Bounding_Coordinate: +26.72

  3. What does it look like?

    <http://geopubs.wr.usgs.gov/open-file/of05-1411/images/cruisemap.jpg> (JPEG)
    Map of Northern Gulf of Mexico showing areas of 2003 USGS seismic research cruise

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date: 29-Apr-2003
    Ending_Date: 16-May-2003
    Currentness_Reference:
    Data assumed to be constant over time, but may change due to geologic processes.

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: seismic reflection profile section

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      Indirect_Spatial_Reference:
      Horizontal X and Y locations for each shot location are provided in ASCII position files.

    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 0.00001. Longitudes are given to the nearest 0.00001. Latitude and longitude values are specified in decimal degrees.

      The horizontal datum used is WGS 84.
      The ellipsoid used is WGS 84.
      The semi-major axis of the ellipsoid used is 6378137 m.
      The flattening of the ellipsoid used is 1/298.257.

  7. How does the data set describe geographic features?

    Entity_and_Attribute_Overview:
    Binary data file: Each profile is available as a binary file in Society of Exploration Geophysicists SEG-Y format. A SEG-Y file consists of 1) a 3200-byte file identification record of EBCDIC encoded general information; 2) a 400-byte binary record with information such as sample rate and record length specific to the data set; and 3) multiple records, one seismic reflection trace per record. Each trace record is preceded by a 240-byte "trace header" containing information such as trace number and acquisition day and time specific to each trace. The trace data are represented as a time series of unitless 16-bit integer or 32-bit real numbers proportional to the pressure recorded at each hydrophone. The SEG-Y file is useful only if you have access to specialized software designed to process and display seismic reflection data.
    Entity_and_Attribute_Detail_Citation:
    Barry, K.M., Cavers, D.A., and Kneale, C.W., 1975, Recommended standards for digital tape formats: Geophysics, v. 40, n. 2, p. 344 - 352. Also available online at: <http://www.seg.org/publications/tech-stand/index_body.html>
    Entity_and_Attribute_Overview:
    Graphic image file: Each profile is available as a JPEG image.

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

    • Patrick E. Hart
    • Deborah R. Hutchinson
    • Myung Lee

  2. Who also contributed to the data set?

  3. To whom should users address questions about the data?

    Patrick E. Hart
    U.S. Geological Survey
    geophysicist
    USGS, MailStop 999, 345 Middlefield Road
    Menlo Park, CA 94025-3561
    USA

    (650) 329-5160 (voice)
    hart@usgs.gov

Why was the data set created?

Marine seismic reflection data are used to image and map sedimentary and structural features of the seafloor and subsurface. These data were acquired across the upper and middle continental slope of the northern Gulf of Mexico as part of an investigation of the of the seismic character, distribution, and potential effects of naturally-occurring marine gas hydrates and related free gas within the gas hydrate stability zone. The specific objectives of this investigation are: (a) To provide site survey information for the two JIP drilling sites/lease blocks (Keathley Canyon 195 and Atwater Valley 14). (b) To tie the new data to regional coverages in the Gulf. (c) To tie the Marion Dufresne coring sites into the regional MCS grid. (d) To provide baseline information for selecting targets for the August NRL/DOE Gyre cruise. The seismic profiles provide high-quality images with approximately 5 meters of vertical resolution and up to 2 km of subbottom penetration.

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: 2003 (process 1 of 4)
    2003 multichannel seismic data acquisition: Acquisition and recording of air-gun and water-gun seismic reflection data. The source consisted of either a 13/13 cubic inch dual-chamber GI ("Generator-Injector") air gun, a 24/24 cubic inch GI air gun, or a 15 cubic inch water gun. The "injector" chamber of the GI gun was timed to discharge a short time (typically 20-30 msec) after the "generator" chamber so as to suppress the bubble pulse and create an optimal signal. The streamer was 240 meters in length with a 10-meter group interval (three hydrophones per group), and was manufactured by Innovative Transducers, Inc. (ITI) with solid-core construction and "thin-film" cylindrical hydrophones of polyvinylidene fluoride (PVDF) plastic. A problem with a streamer connection caused the far 2 channels to be very noisy, and these channels were eliminated during data processing. Data were digitized with the Geometrics Strataview seismograph and recorded with the Geometrics Marine Controller in SEG-D format.

    Date: 2003 (process 2 of 4)
    Multichannel data processing: A representative data processing sequence consisted of: 1. SEG-D input and resample to 1.0 millisecond; 2. Geometry assignment and sort to CDP at 5 m spacing; 3. Wavelet deconvolution (Derived wavelet using 3 shot gathers and 16-18 msec window); 4. Predictive deconvolution (1st-zero crossing, operator length = 60 msec and a single design window); 5. Trace edit ; 6. Single window balance; 7. Band-pass filtering; 8. Common-Offset DMO; 9. Velocity analysis and NMO; 10. Stack (12-fold where 10 m shot spacing, 6-fold where 20 m shot spacing, 4-fold where 30-m shot spacing); 11. True amplitude gain application on stacked data; 12. Post-stack 2nd-zero crossing deconvolution (Operator length = 30 msec and single design window); 13. Migration velocity analysis based on the stacking velocity: Iteratively adjusted; 14. Migration; 15. Post-stack 40-400 Hz band-pass filtering ; 16. Water-bottom mute.

    Date: 2003 (process 3 of 4)
    Positional (navigation) data: As the seismic reflection data were acquired, the position of the vessel was continuously determined with the differnetial Global Positioning System (GPS). GPS positions were recorded approximately every second, and written to an ASCII file. This file was subsequently used to determine the position of each seismic reflection "shotpoint".

    Date: 2004 (process 4 of 4)
    Open File preparation The migrated seismic profiles were converted from SEG-Y format to CGM plot files using Paradigm Focus software. Then the CGM files were converted to 300 dots per inch JPEG image file using Larson CGM to Image software.

    Person who carried out this activity:

    Patrick E. Hart
    U.S. Geological Survey
    geophysicist
    USGS, MailStop 999, 345 Middlefield Road
    Menlo Park, CA 94025-3561
    USA

    (650) 329-5160 (voice)
    hart@usgs.gov

  3. What similar or related data should the user be aware of?

    Hutchinson, Deborah R. , and Hart, Patrick E. , 2003, Cruise Report for G1-03-GM, USGS Gas Hydrates Cruise, R/V Gyre, 1-14 May 2003, Northern Gulf of Mexico: USGS Open-File Report 03-474, U. S. Geological SurveyCross_Reference, Woods Hole, MA.

    Other_Citation_Details: <http://pubs.usgs.gov/of/2003/of03-474/>
    Hart, Patrick E. , Cooper, Alan K. , Twichell, David, Lee, Myung, and Agena, Warren, 2002, High-Resolution Multichannel Seismic-Reflection Data Acquired in the Northern Gulf of Mexico, 1998-99: USGS Open-File Report 02-368, U. S. Geological Survey, Menlo Park, CA.

    Other_Citation_Details: <http://geopubs.wr.usgs.gov/open-file/of02-368/>
    Lee, Myung, Hart, Patrick E. , and Agena, Warren, 2000, Processing Strategy for Water-Gun Seismic Data from the Gulf of Mexico: USGS Bulletin 2181, U. S. Geological Survey, Denver, CO.

    Other_Citation_Details: <http://greenwood.cr.usgs.gov/pub/bulletins/b2181/>
    United States Geological Survey, Coastal and Marine Geology (CMG), 2005, USGS Coastal & Marine Geology InfoBank, USGS CMG G-1-03-GM Metadata.

    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 seismic reflection profiles is highly qualitative, and depends on equipment and operating condition variables too numerous to quantify. There have been no efforts to assess the validity of the data.

  2. How accurate are the geographic locations?

    Positions were determined with differential Global Positioning System (GPS). Absolute position accuracy was approximately plus/minus 10 m.

  3. How accurate are the heights or depths?

    The vertical position was local sea level and there have been no corrections to a datum or for tidal variations.

  4. Where are the gaps in the data? What is missing?

    These are sparse line coverages (2D). Therefore, data are inherently incomplete. Geologic details between lines must be inferred. The surveys were not designed to cover a particular geographic area; the line spacings and azimuths were chosen to assess geologic features related to known and inferred gas hydrate deposits.

  5. How consistent are the relationships among the observations, including topology?

    These data have not been assessed for internal consistency.

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:
The U.S. Geological Survey requests to be acknowledged as the originator of the data in future products or derivative research.

  1. Who distributes the data set? (Distributor 1 of 1)

    Patrick E. Hart
    U.S. Geological Survey
    geophysicist
    USGS, MailStop 999, 345 Middlefield Road
    Menlo Park, CA 94025-3561
    USA

    (650) 329-5160 (voice)
    hart@usgs.gov

    Contact_Instructions:
    Data may be available off-line only by special arrangement with the distributor above. Please use the on-line download option unless precluded by download times or access difficulties.
  2. What's the catalog number I need to order this data set?

    U.S. Geological Suvey Open-File Report 05-1411

  3. What legal disclaimers am I supposed to read?

    This dataset 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 information, apparatus, products, or processes disclosed in this report, nor represents that its use would not infringe privately owned rights. 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. Although all data published in this report 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. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of this data.

  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 software, such as ProMax and Seisworks by Landmark Geophysical; FOCUS and SeisX by Paradigm Geophysical; SPW by Parallel Geoscience; or VISTA by Seismic Image Software.

Who wrote the metadata?

Dates:
Last modified: 22-Aug-2005
Metadata author:
Patrick E. Hart
U.S. Geological Survey
geophysicist
USGS, MailStop 999, 345 Middlefield Road
Menlo Park, CA 94025-3561
USA

(650) 329-5160 (voice)
hart@usgs.gov

Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

Generated by mp version 2.8.11 on Thu Aug 18 13:06:28 2005

http://pubs.usgs.gov/of/2005/1411/faq.html
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last modified 17 October 2005 (pjt)

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