SEG-Y format of chirp seismic data collected offshore of the Chandeleur Islands, LA, 2007

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Frequently anticipated questions:


What does this data set describe?

Title:
SEG-Y format of chirp seismic data collected offshore of the Chandeleur Islands, LA, 2007
Abstract:
In 2006 and 2007, the U.S. Geological Survey, in partnership with Louisiana Department of Natural Resources and the University of New Orleans, conducted geologic mapping to characterize the sea floor and shallow subsurface stratigraphy offshore of the Chandeleur Islands in Eastern Louisiana. The mapping was carried out during two cruises on the R/V Acadiana. Data were acquired with the following equipment: an SEA Ltd SwathPlus interferometric sonar (234 kHz), Klein 3000 dual frequency sidescan sonar, and an Edgetech 512i chirp subbottom profiling system. The long-term goal of this mapping effort is to produce high-quality geologic maps and geophysical interpretations that can be utilized to investigate the impact of Hurricane Katrina in 2005 and to identify sand resources within the region.
Supplemental_Information:
For more information on the seismic surveys see https://cmgds.marine.usgs.gov/fan_info.php?fan=2007-007-FA. These data are also available via GeoMapApp (http://www.geomapapp.org/) and Virtual Ocean (http://www.virtualocean.org/) earth science exploration and visualization applications.
The JPEG format of these data (along with other data associated with this field activity) were released through the Open-File Report 2008-1195 (https://pubs.usgs.gov/of/2008/1195/). See the cross-reference for full citation information.
  1. How might this data set be cited?
    U.S. Geological Survey, 2009, SEG-Y format of chirp seismic data collected offshore of the Chandeleur Islands, LA, 2007: U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -89.293553
    East_Bounding_Coordinate: -88.883122
    North_Bounding_Coordinate: 29.661442
    South_Bounding_Coordinate: 29.381022
  3. What does it look like?
    https://pubs.usgs.gov/of/2008/1195/images/seis_imag.jpg (JPEG)
    JPEG image of seismic-reflection profile
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 10-Jun-2007
    Ending_Date: 22-Jun-2007
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: raster digital data
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Raster data set. It contains the following raster data types:
      • Dimensions, type pixel
    2. What coordinate system is used to represent geographic features?
  7. How does the data set describe geographic features?

Who produced the data set?

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

    (508) 548-8700x2266 (voice)
    (508) 457-2310 (FAX)
    dtwichell@usgs.gov

Why was the data set created?

These chirp seismic-reflection data were collected to use for interpretation of shallow subsurface stratigraphy offshore the Chandeleur Islands, Louisiana.

How was the data set created?

  1. From what previous works were the data drawn?
    Information unavailable from original metadata. (source 1 of 1)
    U.S. Geological Survey, unknown, Information unavailable from original metadata..

    Type_of_Source_Media: disc
    Source_Contribution:
    Approximately 1655 km of high-resolution chirp seismic-reflection profiles were collected using an EdgeTech Geo-Star FSSB system and an SB-0512i towfish (0.5-12 kHz) on the R/V Acadiana of Loreauville, LA. EdgeTech J-Star acquisition software was used to control the Geo-Star topside unit and digitally log trace data in the JSF format. Data were acquired using a 0.25-s fire rate, a 5-ms pulse length, and a 0.5 to 8 kHz sweep (swept frequency). Tracklines are spaced 100 to 125 m apart in the shore parallel direction and about 1 km apart in the shore perpendicular direction.
  2. How were the data generated, processed, and modified?
    Date: 2007 (process 1 of 9)
    jsftosegy (no version), a C script developed by Tom O'Brien (USGS - Woods Hole Seafloor Mapping Group) was used to convert raw chirp traces in the JSF format to chirp-processed, envelope traces in the SEG-Y rev. 1 standard format. Person who carried out this activity:
    Wayne E. Baldwin
    U.S. Geological Survey
    Geologist
    384 Woods Hole Rd.
    Woods Hole, MA

    (508) 548-8700x2226 (voice)
    (508) 457-2310 (FAX)
    wbaldwin@usgs.gov
    Date: 2006 (process 2 of 9)
    A script was run that used SIOSEIS (version 96.4) to shift all traces by -2 ms vertically to account for the position of the 512i towfish beneath the sea surface. A second SIOSEIS script was used to predict the vertical location of the sea floor by identifying peak amplitudes within a vertical window. Two-way travel times (milliseconds) to the sea floor at each trace were recorded to an ASCII text file. Person who carried out this activity:
    Wayne E. Baldwin
    U.S. Geological Survey
    Geologist
    384 Woods Hole Rd.
    Woods Hole, MA

    (508) 548-8700x2226 (voice)
    (508) 457-2310 (FAX)
    wbaldwin@usgs.gov
    Date: 2006 (process 3 of 9)
    All SEG-Y trace data were imported into Seisworks 2-D(version: R2003.12.0.0; Landmark Graphics Corp.), a 2-dimensional, digital seismic interpretation software, and seafloor values were imported as Seisworks horizon data. Spurious seafloor values were edited for discrete traces through heads-up digitization of the Seisworks horizon, and corrected values were exported to a new ASCII text file. Person who carried out this activity:
    Wayne E. Baldwin
    U.S. Geological Survey
    Geologist
    384 Woods Hole Rd.
    Woods Hole, MA

    (508) 548-8700x2226 (voice)
    (508) 457-2310 (FAX)
    wbaldwin@usgs.gov
    Date: 2006 (process 4 of 9)
    An additional script was run that used SIOSEIS to remove sea surface heave and mute water column portions of the traces by: 1) loading the corrected seafloor times into the SEG-Y trace headers; 2) smoothing the sea floor picks using an along-track filter that approximates twice the period of sea surface heave to be removed (the filter window was set to use 46 traces); 3) creating a series of difference values between the raw and smoothed seafloor picks for each trace; 4) shifting traces up or down according to the difference values; and 5) muting each trace between time zero and the time of the smoothed sea floor pick, thus removing noise within the water column. Changes to the traces within each profile were saved to new "heave corrected" SEG-Y files, which were used for creation of JPEG browse images and digital interpretation. Person who carried out this activity:
    Wayne E. Baldwin
    U.S. Geological Survey
    Geologist
    384 Woods Hole Rd.
    Woods Hole, MA

    (508) 548-8700x2226 (voice)
    (508) 457-2310 (FAX)
    wbaldwin@usgs.gov
    Date: 2006 (process 5 of 9)
    A script was run that used Seismic Unix (version 4.1) to read the SEG-Y files and plot the data as 8-bit gray scale Postscript files using the Seismic Unix 'psimage' algorithm. All images were created with a horizontal scale of 200 traces per inch. Images were plotted within a constant 8-inch vertical window of 50 milliseconds (Two-Way Travel Time) duration, yielding a vertical resolution of about 8.3 milliseconds per inch. The Postscript images were then converted to JPEG format using ImageMagick (version 5.5.6). Person who carried out this activity:
    Wayne E. Baldwin
    U.S. Geological Survey
    Geologist
    384 Woods Hole Rd.
    Woods Hole, MA

    (508) 548-8700x2226 (voice)
    (508) 457-2310 (FAX)
    wbaldwin@usgs.gov
    Date: 28-Feb-2017 (process 6 of 9)
    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. Fixed an online link in a cross-reference. The distribution format name was modified in an attempt to be more consistent with other metadata files of the same data format. 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-Nov-2017 (process 7 of 9)
    This metadata record was modified from one describing JPEG images to reflect the SEG-Y version of the same data (Open-File Report 2008-1195, https://pubs.usgs.gov/of/2008/1195/). Changes were made to the Citation and Distribution_Information. 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: 30-Nov-2017 (process 8 of 9)
    Keywords section of metadata optimized for discovery in USGS Coastal and Marine Geology Data Catalog. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Alan O. Allwardt
    Contractor -- Information Specialist
    2885 Mission Street
    Santa Cruz, CA

    831-460-7551 (voice)
    831-427-4748 (FAX)
    aallwardt@usgs.gov
    Date: 08-Sep-2020 (process 9 of 9)
    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?
    Stockwell, John, 2008, CWP/SU: Seismic Uni*x: Center for Wave Phenomena - Colorado School of Mines, Golden, CO.

    Online Links:

    Henkart, Paul, 2007, SIOSEIS: Scripps Institution of Oceanography, University of California - San Diego, LaJolla, CA.

    Online Links:

    Michael W. Norris and Alan K. Faichney, 2002, SEGY Rev.1 Data Exchange Format1: Society of Exploration Geophysicists, Tulsa, OK.

    Online Links:

    Baldwin, Wayne E., Pendleton, Elizabeth A., and Twichell, David C., 2009, Geophysical Data from offshore of the Chandeleur Islands, Eastern Mississippi Delta: Open-File Report 2008-1195, U.S. Geological Survey, Reston, VA.

    Online Links:


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 SB-0512i was towed approximately 6 m astern and approximately 1.5 m below the sea surface. DGPS navigation (assumed to be accurate within 1-2 m) was obtained from the receiver mounted above the interferometric sonar head, but towfish layback was not accounted for. The layback of the towfish adds additional uncertainty due to changes in angle and scope of the tow cable in response to sea state and vessel speed. The use of J-Star acquisition software during the ACAD07007 cruise caused a reduction in the resolution of navigation values recorded to the trace headers from the onboard DGPS. During acquisition, J-Star truncates the three least significant digits from the raw navigation string, which reduces the resolution of each navigation fix on the order of 1-2 meters. This error is evident in the ship-track polylines in the shapefile "seismic_trk_07007.shp", which display a "sawtooth" pattern when viewed at scales finer than approximately 1:3000. Based on horizontal offsets between the fish and GPS receiver, fish motion behind the vessel, and error associated with the acquisition system, the resulting positional accuracy is assumed to be +/- 20 m.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    All acquired seismic data were processed and JPEG images produced.
  5. How consistent are the relationships among the observations, including topology?
    Processed seismic data were converted to JPEG format for ease of seismic trace display. Quality control was conducted during processing.
    Data Quality Problems: Poor sea-state conditions periodically created problems with acquisition of the chirp seismic data during the ACAD07007 cruise. In most instances, heave removal processing (described in processing steps 2-4) greatly minimized the effects of sea state in the final trace data. However, the effects of particularly larger swells do remain within some of the final profiles. In the interest of preserving as much potentially interesting seafloor information as possible, we decided not to lengthen seafloor smoothing filters to the widths that would have been required to remove larger swells. We suggest viewing the JPEG image of line l44f1_000_h.jpg as a reference for the type of seismic artifacts that have been introduced as a result of excessive heave. In general, the artifacts will typically consist of a predictably undulating seafloor reflection that will often be accompanied by a reduction in along-track balance of the seismic traces (ie. vertical striping that alternates between lighter and darker groups of traces, producing a "fencepost"-like appearance). In light of these problems, we caution the interpretation of seafloor features that appear to be at the same scale of heave artifacts within profiles that are obviously affected by problematic sea states.

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 as the originator of the dataset.
  1. Who distributes the data set? (Distributor 1 of 1)
    Wayne E. Baldwin
    U.S. Geological Survey
    Geologist
    384 Woods Hole Rd.
    Woods Hole, MA

    (508) 548-8700x2226 (voice)
    (508) 457-2310 (FAX)
    wbaldwin@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?
    Neither the U.S. Government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights. 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?
  5. What hardware or software do I need in order to use the data set?
    These data require software that can read SEG-Y data.

Who wrote the metadata?

Dates:
Last modified: 08-Sep-2020
Metadata author:
Wayne E. Baldwin
U.S. Geological Survey
Geologist
384 Woods Hole Rd.
Woods Hole, MA

(508) 548-8700x2226 (voice)
(508) 457-2310 (FAX)
wbaldwin@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/segy/07007_segy.faq.html>
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