High-resolution multichannel seismic-reflection data acquired in the northern Gulf of Mexico, 1998-99

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Frequently anticipated questions:


What does this data set describe?

Title:
High-resolution multichannel seismic-reflection data acquired in the northern Gulf of Mexico, 1998-99
Abstract:
This report consists of two-dimensional marine seismic reflection profile data from the northern Gulf of Mexico. These data were acquired in 1998 and 1999 with the Research Vessels Tommy Munro (M1-98-GM) and Gyre (G1-99-GM). The data are available in binary and GIF 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 GIF 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 propogates 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 surveys M1-98-GM and G1-99-GM are available at
 http://walrus.wr.usgs.gov/infobank/m/m198gm/html/m-1-98-gm.meta.html
 The data window for M1-98-GM is -89.941 28.024 -88.995 28.656 (decimal degrees).
 http://walrus.wr.usgs.gov/infobank/g/g199gm/html/g-1-99-gm.meta.html
 The data window for G1-99-GM is -92.991 27.368 -91.429 27.944 (decimal degrees).
  1. How might this data set be cited?
    Hart, Patrick E., Cooper, Alan K., and Twichell, David, 2002, High-resolution multichannel seismic-reflection data acquired in the northern Gulf of Mexico, 1998-99: U.S. Geological Survey Open-File Report 02-368, U.S. Geological Survey, Menlo Park, CA.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -93.00
    East_Bounding_Coordinate: -89.00
    North_Bounding_Coordinate: +28.67
    South_Bounding_Coordinate: +27.37
  3. What does it look like?
    http://pubs.usgs.gov/of/2002/of02-368/images/cruisemap.jpg (JPEG)
    Map of Northern Gulf of Mexico showing areas of USGS seismic research cruises, 708x316 pixels, 73k bytes
    http://pubs.usgs.gov/of/2002/of02-368/images/99gif/41.gif (GIF)
    Gulf of Mexico seismic line 41.gif (water-gun source), 4139x921 pixels, 424k bytes
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 1998
    Currentness_Reference:
    Ground condition. 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?
      This is a Point data set. It contains the following vector data types (SDTS terminology):
      • Entity point
    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.
      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/Portals/0/SEG/News%20and%20Resources/Technical%20Standards/seg_y_rev1.pdf

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
    • Alan K. Cooper
    • David Twichell
  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
    Mail Stop 999, 345 Middlefield Rd.
    Menlo Park, CA
    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 produce high-resolution images of the gas hydrate stability zone; (b) to study the distribution and character of potential seafloor failures and their relationship to known and inferred gas hydrate deposits; (c) to look at systematic variations in subsurface structure in gas hydrate and non-hydrate areas; and (d) to estimate, if possible, the amounts of hydrates present within the gas hydrate stability zone. The seismic profiles provide high-quality images with approximately 5 meters of vertical resolution and up to 2 km of 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: 1998 (process 1 of 6)
    1998 multichannel seismic data acquisition:
    Acquisition and recording of air-gun and water-gun seismic reflection data. The source consisted of either a 35/35 cubic inch dual-chamber GI ("Generator-Injector") 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 7 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: 1999 (process 2 of 6)
    1999 multichannel seismic data acquisition:
    The multichannel data acquisition equipment and parameters in 1999 were the same as 1998 except the 15 cubic inch water-gun source was used on all lines, and the recording problem with the far 7 streamer channels was corrected.
    Date: 1999 (process 3 of 6)
    Multichannel data processing: A representative data processing sequence consisted of:
    1. SEG-D input and resample to 0.5 millisecond
    2. Trace edit
    3. Geometry assignment
    4. 50 Hz low-cut filter
    5. Water-bottom mute
    6. Deep-water recording delay correction
    7. Spherical divergence correction
    8. Noise-spike editing
    9. FK filter
    10. Deconvolution
    11. Common midpoint (CMP) sort
    12. Stacking velocity analysis
    13. Normal move-out correction
    14. Stack
    15. SEG-Y output
    16. 60-320 Hz bandpass filter
    17. Whole-trace balance
    18. gif image file output
    
    Date: Jun-1998, 199904 (process 4 of 6)
    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: 2001 (process 5 of 6)
    The data were plotted in 8-bit gray scale representation to Postscript files using the Seismic Unix 'psimage' algorithm at a scale of 0.15 seconds per inch and 75 traces per inch. The Postscript images were then converted to GIF with Aladdin Ghostview v5.50. Person who carried out this activity:
    Patrick E. Hart
    U.S. Geological Survey
    geophysicist
    Mail Stop 999, 345 Middlefield Rd.
    Menlo Park, CA
    USA

    (650) 329-5160 (voice)
    hart@usgs.gov
    Date: 16-Sep-2002 (process 6 of 6)
    Creation of original metadata record Person who carried out this activity:
    Patrick E. Hart
    U.S. Geological Survey
    geophysicist
    Mail Stop 999, 345 Middlefield Rd.
    Menlo Park, CA
    USA

    (650) 329-5160 (voice)
    hart@usgs.gov
  3. What similar or related data should the user be aware of?
    Cooper, Alan K., and Hart, Patrick E., 2002, High-resolution seismic-reflection investigation of the northern Gulf of Mexico gas-hydrate-stability zone: Elsevier Sciences, Ltd, Great Britain.

    Cooper, Alan K., Hart, Patrick E., and Pecher, Ingo, 1998, Cruise report for a seismic investigation of gas hydrates in the Mississippi Canyon region, northern Gulf of Mexico - Cruise M1-98-GM,: U.S. Geological Survey Open-File Report 98-506, U. S. Geological Survey, Menlo Park, CA.

    Online Links:

    Cooper, Alan K., Twichell, David, and Hart, Patrick E., 1999, A seismic-reflection investigation of gas-hydrates and sea-floor features of the upper continental slope of the Garden Banks and Green Canyon regions, northern Gulf of Mexico: Report for cruise G1-99-GM (99002): U.S. Geological Survey Open-File Report 99-570, U. S. Geological SurveyCross_Reference, Menlo Park, CA.

    Online Links:

    Lee, Myung, Hart, Patrick E., and Agena, Warren, 2000, Processing strategy for water-gun seismic data from the Gulf of Mexico: U.S. Geological Survey Bulletin 2181, U. S. Geological Survey, Denver, CO.

    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 ± 10 m.
  3. How accurate are the heights or depths?
    The vertical position was local sea level and there has 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
    Mail Stop 999, 345 Middlefield Rd.
    Menlo Park, CA
    USA

    (650) 329-5160 (voice)
    hart@usgs.gov
  2. What's the catalog number I need to order this data set? USGS Open-File Report 02-368
  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 on this CD-ROM 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: 10-Jun-2016
Metadata author:
Peter N Schweitzer
USGS Midwest Area
Collection manager, USGS Geoscience Data Clearinghouse, http://geo-nsdi.er.usgs.gov/
Mail Stop 954
12201 Sunrise Valley Dr
Reston, VA
USA

703-648-6533 (voice)
703-648-6252 (FAX)
pschweitzer@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

This page is <https://geo-nsdi.er.usgs.gov/metadata/open-file/02-368/metadata.faq.html>
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