Archive of Digital Chirp Subbottom Profile Data Collected During USGS Cruise 12BIM03 Offshore of the Chandeleur Islands, Louisiana, July 2012

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Frequently anticipated questions:


What does this data set describe?

Title:
Archive of Digital Chirp Subbottom Profile Data Collected During USGS Cruise 12BIM03 Offshore of the Chandeleur Islands, Louisiana, July 2012
Abstract:
In July of 2012, the U.S. Geological Survey conducted a geophysical survey offshore of the Chandeleur Islands, La. to investigate the geologic controls on barrier island framework. This report serves as an archive of unprocessed digital chirp subbottom data, trackline maps, navigation files, Geographic Information System (GIS) information, and formal Federal Geographic Data Committee (FGDC) metadata. Gained digital images of the seismic profiles 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). Examples of SU processing scripts and USGS software for viewing the SEG Y files (Zihlman, 1992) are also provided. 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 also be downloaded from the USGS Coastal and Marine Geoscience Data System (<http://cmgds.marine.usgs.gov>).
Supplemental_Information:
The USGS Saint Petersburg Coastal and Marine Science Center (SPCMSC) - St. Petersburg, Fla., assigns a unique identifier to each cruise or field activity. For example, 12BIM03 tells us the data were collected in 2012 during the third field activity for that project in that calendar year. Refer to <http://walrus.wr.usgs.gov/infobank/programs/html/definition/activity.html> for a detailed description of the method used to assign the cruise ID. The naming convention used for each subbottom line is as follows: yye##a, where 'yy' are the last two digits of the year in which the data were collected, 'e' is a 1-letter abbreviation for the equipment type (for example, c for 424 chirp), '##' is a 2-digit number representing a specific track, and 'a' is a letter representing the section of a line if recording was prematurely terminated or rerun for quality or acquisition problems. All Chirp systems use a signal of continuously varying frequency; the system used during this survey produces high-resolution, shallow-penetration (typically less than 50-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, some energy is reflected back toward the transducer, received, and recorded by a PC-based seismic acquisition system. This process is repeated at regular time 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 (2-D) vertical image of the shallow geologic structure beneath the towfish is produced. The seismic source utilized during 12BIM03 consisted of an EdgeTech SB-424 towfish running DISCOVER v. 3.51 acquisition software and towed 4 m behind the GPS antenna. The data were acquired using a frequency sweep of 4 - 20 kHz, a 43 kHz sample frequency, and a record length of approximately 30 ms . Based on survey speeds of 3.5 knots, the shot spacing was about 0.450 m. The binary portion of the unprocessed seismic data are stored in SEG Y rev. 0 (Barry and others, 1975), 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 ASCII format instead of EBCDIC format. The SEG Y formatted trace files have a .sgy extension. The SEG Y files may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU) (Cohen and Stockwell, 2010). Also provided are examples of SU scripts that allow users to remove navigation fixes from the SEG Y headers, along with the fix provided for every 1,000 shots, and produce a printable, gained GIF image of each profile. The printable profiles provided here are GIF images gained using SU software. Refer to the Software page of this report for links to example SU processing scripts and USGS software for viewing the SEG Y files (Zihlman, 1992).
  1. How might this data set be cited?
    Forde, Arnell S., Miselis, Jennifer L., and Wiese, Dana S., 2014, Archive of Digital Chirp Subbottom Profile Data Collected During USGS Cruise 12BIM03 Offshore of the Chandeleur Islands, Louisiana, July 2012: U.S. Geological Survey Data Series 856, U.S. Geological Survey, St. Petersburg, Fla..

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -88.916378
    East_Bounding_Coordinate: -88.797183
    North_Bounding_Coordinate: 30.094522
    South_Bounding_Coordinate: 29.951025
  3. What does it look like?
    <http://pubs.usgs.gov/ds/856/maps/12bim03_location.jpg> (JPEG)
    Figure 3. Location map of all digital chirp subbottom data collected during USGS Field Activity 12BIM03. This map was created at a scale of 1:125,000.
    <http://pubs.usgs.gov/ds/856/maps/12bim03_area1.jpg> (JPEG)
    Figure 4. Area 1 detailed trackline map of digital chirp subbottom data collected during USGS Field Activity 12BIM03. This map was created at a scale of 1:27,450.
    <http://pubs.usgs.gov/ds/856/maps/12bim03_area2.jpg> (JPEG)
    Figure 5. Area 2 detailed trackline map of digital chirp subbottom data collected during USGS Field Activity 12BIM03. This map was created at a scale of 1:27,450.
    <http://pubs.usgs.gov/ds/856/maps/12bim03_area3.jpg> (JPEG)
    Figure 6. Area 3 detailed trackline map of digital chirp subbottom data collected during USGS Field Activity 12BIM03. This map was created at a scale of 1:27,450.
    <http://pubs.usgs.gov/ds/856/maps/12bim03_area4.jpg> (JPEG)
    Figure 7. Area 4 detailed trackline map of digital chirp subbottom data collected during USGS Field Activity 12BIM03. This map was created at a scale of 1:30,000.
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 23-Jul-2012
    Ending_Date: 31-Jul-2012
    Currentness_Reference:
    Data collection interval
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: Tabular, vector, and raster digital data
  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 (latitude and longitude and Zone 16 UTM coordinates) for each shot are provided as ASCII text files, along with the date and time (UTC) the shot was recorded.
    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 0.0197885540. Longitudes are given to the nearest 0.0227288676. Latitude and longitude values are specified in Decimal Degrees. The horizontal datum used is D WGS 84.
      The ellipsoid used is WGS 1984.
      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?
    12bim03.txt, s12bim03.txt, and 12bim03_s.txt
    Shotpoint navigation files (Source: SEG Y headers (<http://www.seg.org/publications/tech-stand>).)
    FID*
    Internal feature number. (Source: Esri) Sequential unique whole numbers that are automatically generated.
    Shape*
    Feature geometry. (Source: Esri) Coordinates defining the features.
    UTMX
    UTM-X coordinate (Zone 16) (Source: Universal Transverse Mercator Geographic Coordinate System)
    Range of values
    Minimum:315283
    Maximum:326627
    Units:meters
    UTMY
    UTM-Y coordinate (Zone 16) (Source: Universal Transverse Mercator Geographic Coordinate System)
    Range of values
    Minimum:3314720
    Maximum:3330738
    Units:meters
    Line
    Trackline number (Source: U.S. Geological Survey) The naming convention used for each subbottom line is as follows: yye##a, where 'yy' are the last two digits of the year in which the data were collected, 'e' is a 1-letter abbreviation for the equipment type (for example, c for Chirp), '##' is a 2-digit number representing a specific track, and 'a' is a letter representing the section of a line if recording was prematurely terminated or rerun for quality or acquisition problems.
    Shot
    Shotpoint number (Source: U.S. Geological Survey)
    Range of values
    Minimum:1
    Maximum:12389
    Lon
    Longitude (decimal degrees) (Source: World Geodetic System 1984 Geographic Coordinate System)
    Range of values
    Minimum:-88.916378
    Maximum:-88.797183
    Units:decimal degrees
    Lat
    Latitude (decimal degrees) (Source: World Geodetic System 1984 Geographic Coordinate System)
    Range of values
    Minimum:29.951025
    Maximum:30.094522
    Units:decimal degrees
    YEAR
    Year (Source: U.S. Geological Survey)
    Range of values
    Minimum:2012
    Maximum:2012
    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: Trace data are available as binary files in SEG Y format. These files have a .sgy extension and range in size from 1.4 to 58.2 MB. These data can be found by going to <http://cmgds.marine.usgs.gov>.
    Entity_and_Attribute_Overview:
    Graphic image file: Printable versions of the subbottom profiles are available as GIF images, links to these images can be found on the Profiles page of this report or by going to <http://pubs.usgs.gov/ds/856/profiles/printable/>.
    Entity_and_Attribute_Overview:
    Navigation file: Navigation files are available as ASCII text files. Provided are raw (unprocessed) shotpoint navigation files (12c**.txt), processed shotpoint navigation (12bim03.txt), processed 1,000-shot-interval location (s12bim03.txt), and a start of line file (12bim03_s.txt). Fields/Attributes [FID, Shape] marked above with an asterisk (*) were created by Esri ArcGIS and are used exclusively by the shapefiles created from the three aforementioned .txt files; these fields are not included in the original navigation files. All remaining attributes listed above in the Entity_and_Attribute_Information: section that do not have an accompanying asterisk are found in 12bim03.txt, s12bim03.txt, and 12bim03_s.txt. Raw and processed navigation data files can be found by going to <http://pubs.usgs.gov/ds/856/nav/>.
    Entity_and_Attribute_Overview:
    GIS file: The GIS data is provided as a .zip file composed of Esri map documents, shapefiles, and metadata.
    Entity_and_Attribute_Detail_Citation: Information is derived from SEG Y headers.

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
    • Jennifer L. Miselis
    • Dana S. Wiese
  2. Who also contributed to the data set?
    Funding and support for this study were provided by the USGS Coastal and Marine Geology Program. We thank R/V Survey Cat captain Nancy DeWitt (SPCMSC) for her assistance in data collection and Will Pfeiffer and Julie Bernier or their assistance with swath data processing. This document was improved by reviews from Kyle Kelso and Ellen Raabe of the USGS - St. Petersburg, Fla. Disc Image Credit: Schmaltz, Jeff, MODIS Rapid Response Team at the NASA Goddard Space Flight Center, 2004, UnitedStates.A2004106.1855.500m.jpg. Also available on-line at <http://eoimages.gsfc.nasa.gov/ve/6886/UnitedStates.A2004106.1855.500m.jpg>
  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) 803-8747 ext. 3111 (voice)
    aforde@usgs.gov

Why was the data set created?

To archive all digital chirp subbottom profile data and associated files collected during cruise 12BIM03.

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: 2013 (process 1 of 5)
    Chirp processing: The SEG Y data were processed with Seismic Unix to produce gained GIF images of the subbottom profiles included in this report. A representative chirp data processing sequence consisted of (1) removing navigation data for each shot and converting it 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 <http://pubs.usgs.gov/ds/856/software/su/readme.txt>. Person who carried out this activity:
    Arnell S. Forde
    U.S. Geological Survey
    Geologist
    600 4th Street South
    St. Petersburg, FL

    (727) 803-8747, ext. 3111 (voice)
    aforde@usgs.gov
    Data sources used in this process:
    • SEG Y
    Data sources produced in this process:
    • printable/SEG Y.gif
    Date: 2013 (process 2 of 5)
    Navigation processing: Shotpoint navigation, start of line, and 1,000-shot-interval location files were extracted using Seismic Unix software and output as ASCII text files; they were then processed with PROJ.4.7.0 (<http://trac.osgeo.org/proj/>) to generate UTM coordinates (WGS84, Zone 16, meters) from latitude and longitude coordinates. Text files for each seismic line were concatenated into comma-delimited text files (for use with Esri software); one containing unique shotpoint positions (12bim03.txt), another containing the 1,000-shot-interval locations (s12bim03.txt) and the last containing start-of-line locations (12bim03_s), which can be viewed within the nav folder. Person who carried out this activity:
    Arnell S. Forde
    U.S. Geological Survey
    Geologist
    600 4th Street South
    St. Petersburg, FL

    (727) 803-8747, ext. 3111 (voice)
    aforde@usgs.gov
    Data sources used in this process:
    • 12c**.txt, 012c**.txt
    Data sources produced in this process:
    • 12bim03.txt
    • s12bim03.txt
    • 12bim03_s.txt
    Date: 2013 (process 3 of 5)
    All concatenated, comma-delimited text files were imported into ArcGIS and saved as either a point or polyline file in the Esri shapefile format. Trackline map creation: the trackline maps was created using Esri ArcGIS 10.1 software. The processed navigation file, 12bim03.txt, was imported into ArcMap 10.1 and processed using the Points to Lines ArcScript to create a line shapefile of the cruise tracklines (12bim03_trkln). The 1,000-shot-interval file, s12bim03.txt, and the start-of-line file, 12bim03_s.txt, were imported into ArcMap as point shapefiles 12bim03_shots and 12bim03_sol. Please refer to the shapefile metadata included in the ArcGIS map document located under the Software section of this archive for additional details. All maps were exported to Adobe Illustrator v. 14 for further editing and then later converted into JPEG format with Adobe Dreamweaver v. 10 Build 4117. The maps are unprojected (geographic coordinates, WGS84). The USGS is the originators of all layers used, with the exception of the basemap (LOSCO). Please see the ArcGIS readme file for detailed information about the GIS files used in this report. Person who carried out this activity:
    Arnell S. Forde
    U.S. Geological Survey
    Geologist
    600 4th Street South
    St. Petersburg, FL

    (727) 803-8747, ext. 3111 (voice)
    aforde@usgs.gov
    Data sources used in this process:
    • 12bim03.txt
    • s12bim03.txt
    • 12bim03_s.txt
    Data sources produced in this process:
    • 12bim03_trkln.shp
    • 12bim03_shots.shp
    • 12bim03_sol.shp
    Date: 2013 (process 4 of 5)
    Data Series preparation: In addition to the process steps described above, the following steps were taken to produce this Data Series report: the handwritten cruise logs were scanned and saved as a PDF file, digital logs were created by A. Forde using the cruise logs and personal accounts of the crew members and saved as PDF files, and an HTML-based format was used to present the various parts of this archive. Person who carried out this activity:
    Arnell S. Forde
    U.S. Geological Survey
    Geologist
    600 4th Street South
    St. Petersburg, FL

    (727) 803-8747, ext. 3111 (voice)
    aforde@usgs.gov
    Date: 24-Jan-2017 (process 5 of 5)
    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
  3. What similar or related data should the user be aware of?
    Cohen, J.K., and Stockwell, J.W., Jr., CWP/SU, 2010, Seismic Unix Release 41: A free package for seismic research and processing, Center for Wave Phenomena, Colorado School of Mines.

    Online Links:

    Zihlman, F.N., USGS, 1992, DUMPSEGY V1.0: A program to examine the contents of SEG Y disk-image seismic data: U.S. Geological Survey Open-File Report 92-590.

    Online Links:

    Other_Citation_Details: 28 pages
    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

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 major anomalies.
  2. How accurate are the geographic locations?
    As the subbottom data were acquired, the position of the vessel was continuously calculated by a CodaOctopus F190 DGPS and subsequently sent to Hypack 2010 navigation software to ensure a consistent grid spacing during data collection. Positions were recorded and written to the trace headers in latitude and longitude coordinates approximately every 1 s using navigation from the CodaOctopus F190 receiver with OmniSTAR High Performance (HP) correction (accurate to within 20 centimeters (cm)). The approximately 4-m offset between the chirp shot and ship's GPS was not accounted for during acquisition, nor have the ASCII navigation files and trackline maps 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?
    These data are collected along tracklines (2-D) and are therefore inherently incomplete. Due to system malfunctions, subbottom data collection did not begin until July 26, 2013 (DOY 208). However, bathymetry and backscatter data were collected during the entire survey period, and this data is available in a separate report (DeWitt et al., 2014).
  5. How consistent are the relationships among the observations, including topology?
    This dataset is 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:
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 Forde
    U.S. Geological Survey
    Geologist
    600 4th Street South
    St. Petersburg, FL
    USA

    (727) 803-8747, ext. 3111 (voice)
    aforde@usgs.gov
    Contact_Instructions:
    All of this report is available online. The SEG Y files are downloadable from the Coastal and Marine Geoscience Data System (<http://cmgds.marine.usgs.gov>).
  2. What's the catalog number I need to order this data set? U.S. Geological Survey Data Series 856
  3. What legal disclaimers am I supposed to read?
    This DVD 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?
    • Availability in digital form:
      Data format: The SEG Y rev. 0 format (Barry and others, 1975) 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. in format SEG Y rev. 0 Size: 2.9 GB
      Media you can order: DVD (format ISO 9660)
      Note: Unix, Linux, DOS, Macintosh
      Data format: The GIS data is composed of map documents, shapefiles, and metadata. Map documents were created with Esri ArcGIS 10.1 software. The shapefiles provided may also be viewed using other versions of Esri desktop software including their free software or ArcGIS Explorer (<http://www.esri.com/software/arcgis/explorer/index.html>). in format map document, shapefile, metadata Size: 127 MB
      Network links: http://pubs.usgs.gov/ds/856/software/arc/arc.zip
    • Cost to order the data: None, if obtained online; otherwise, prices vary.

    • Special instructions:
      Publications are available from USGS Information Services, Box 25286, Federal Center, Denver, CO 80225-0046 (telephone: 1-888-ASK-USGS, e-mail: infoservices@usgs.gov).
  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 (<http://www.cwp.mines.edu/cwpcodes/index.html>).

Who wrote the metadata?

Dates:
Last modified: 24-Jan-2017
Metadata author:
Arnell Forde
U.S. Geological Survey
Geologist
600 4th Street South
St. Petersburg, FL
USA

(727) 803-8747, ext. 3111 (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/12BIM03_chirp-met.faq.html>
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