Archive of Digital CHIRP Seismic Reflection Data Collected During USGS Cruise 06SCC02 Offshore of the Chandeleur Islands, Louisiana, July 2006

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Frequently anticipated questions:

What does this data set describe?

Title:
Archive of Digital CHIRP Seismic Reflection Data Collected During USGS Cruise 06SCC02 Offshore of the Chandeleur Islands, Louisiana, July 2006
Abstract:
In July of 2006, the U.S. Geological Survey conducted geophysical surveys offshore of Chandeleur Islands, LA, and in nearby waterbodies. This report serves as an archive of unprocessed digital CHIRP seismic reflection data, trackline maps, navigation files, GIS information, Field Activity Collection System (FACS) logs, observer's logbook, and formal 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 format (Barry and others, 1975) and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU). Example SU processing scripts and USGS software for viewing the SEG-Y files (Zihlman, 1992) are also provided.
Supplemental_Information:
The USGS Florida Integrated Science Center (FISC) - St. Petersburg assigns a unique identifier to each cruise or field activity. For example, 06SCC02 tells us the data were collected in 2006 for the Subsidence and Coastal Change (SCC) study and the data were collected during the second field activity for that study 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 seismic 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, b for boomer and 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. The CHIRP system uses a signal of continuously varying frequency. The towfish is a sound source and receiver, which is typically towed 2 - 5 m above the seafloor. The acoustic energy is reflected at density boundaries (such as the seafloor or sediment layers beneath the seafloor), detected by a receiver, and recorded by a PC-based seismic acquisition system. This process is repeated at timed intervals (for example, 0.125 s) and recorded for specific intervals of time (for example, 50 ms). In this way, a two-dimensional vertical image of the shallow geologic structure beneath the ship track is produced. The seismic source employed for CHIRP data collection consisted of an EdgeTech SB-424 towfish running Triton Imaging SB Logger (FSSB) V. 1.6.421 acquisition software and towed about 10 m behind the GPS antenna. The frequency range was 4 - 24 kHz. Sample frequency of the data was 25 kHz, and record length was approximately 30 ms. Shot spacing was about 0.645 m. During data collection, a vertical striped pattern was observed in the profiles. This anomaly was caused by an acquisition software malfunction that resulted in zero values for every fifth trace. For each recorded shot of the CHIRP data, three channels of trace data are collected. Channel 2 is the "real," or in-phase component of the signal, channel 1 is the "imaginary," or quadrature component of the signal, and channel 0 is the "envelope," or product of channels 1 and 2. Only channel 0 was used to produce the profiles presented here. However, all channels are included in the SEG-Y data files. The printable profiles provided here are GIF images that were gained using Seismic Unix software. The processed SEG-Y data were exported to Chesapeake Technology, Inc. (CTI) SonarWeb software to produce interactive versions of the profiles, which allow the user to obtain a geographic location and depth from the profile for a cursor position. This information is displayed in the status bar of the browser. NOTE: The only supported Web browsers that properly display all features of the interactive profiles are Internet Explorer 6 for Windows and Firefox 1.5 for all platforms. For all browsers, the status bar and JavaScript must be enabled. Firefox also requires "Change status bar text" to be checked under Advanced JavaScript Settings. Use of other browsers may result in spurious or no information given in the status window. Firefox may be downloaded at http://www.mozilla.org/products/firefox. Postprocessing of the data also revealed the first shot value to be something other than one. The year and date were also omitted from the SEG-Y headers. A conversion program called Fixping V. 1.0.0 was used to correct these three errors. These corrected SEG-Y files are provided in this archive. No navigation fixes were recorded to the SEG-Y headers for tracklines 06c50 - 06c57. The navigation data were stripped from coincident sidescan sonar tracklines and merged with the seismic shotpoints to produce the reconstructed navigation shown on the trackline maps and in the navigation files. The unprocessed seismic data are stored in SEG-Y format, which is a standard digital format that can be read and manipulated by most seismic processing software packages (Barry and others, 1975). The SEG-Y formatted trace files have a .SEG extension. Also provided are example Seismic Unix scripts that allow the user to strip off navigation fixes from the SEG-Y headers, along with a fix for every 1,000 shots and produce a gained GIF image of each profile.
  1. How might this data set be cited?
    Harrison, Arnell S., Dadisman, Shawn V., Flocks, James G., and Wiese, Dana S., 2007, Archive of Digital CHIRP Seismic Reflection Data Collected During USGS Cruise 06SCC02 Offshore of the Chandeleur Islands, Louisiana, July 2006: U.S. Geological Survey Data Series 310, U.S. Geological Survey, St. Petersburg, FL.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -89.010338
    East_Bounding_Coordinate: -88.781778
    North_Bounding_Coordinate: 30.083646
    South_Bounding_Coordinate: 29.632479
  3. What does it look like?
    DVD/maps/cruisenav/06scc02_location_map.jpg (JPEG)
    Location map of all digital CHIRP seismic reflection data collected during USGS Cruise 06SCC02. This map was created at a scale of 1:296,000. Refer to the Lineage section below for the trackline map creation process.
    DVD/maps/cruisenav/06scc02_areaa.jpg (JPEG)
    Trackline map of digital CHIRP seismic reflection data collected in Area A (refer to Area A of the location map) during USGS Cruise 06SCC02. This map was created at a scale of 1:196,000. Refer to the Lineage section below for the trackline map creation process.
    DVD/maps/cruisenav/06scc02_areab.jpg (JPEG)
    Trackline map of digital CHIRP seismic reflection data collected in Area B (refer to Area B of the location map) during USGS Cruise 06SCC02. This map was created at a scale of 1:196,000. Refer to the Lineage section below for the trackline map creation process.
    DVD/maps/cruisenav/06scc02_area1.jpg (JPEG)
    Trackline map of digital CHIRP seismic reflection data collected in Area 1 (refer to Area 1 of the Area A map) during USGS Cruise 06SCC02. This map was created at a scale of 1:185,000. Refer to the Lineage section below for the trackline map creation process.
    DVD/maps/cruisenav/06scc02_area2.jpg (JPEG)
    Trackline map of digital CHIRP seismic reflection data collected in Area 2 (refer to Area 2 of the Area A map) during USGS Cruise 06SCC02. This map was created at a scale of 1:185,000. Refer to the Lineage section below for the trackline map creation process.
    DVD/maps/cruisenav/06scc02_area3.jpg (JPEG)
    Trackline map of digital CHIRP seismic reflection data collected in Area 3 (refer to Area 3 of the Area A map) during USGS Cruise 06SCC02. This map was created at a scale of 1:185,000. Refer to the Lineage section below for the trackline map creation process.
    DVD/maps/cruisenav/06scc02_area4.jpg (JPEG)
    Trackline map of digital CHIRP seismic reflection data collected in Area 4 (refer to Area 4 of the Area B map) during USGS Cruise 06SCC02. This map was created at a scale of 1:185,000. Refer to the Lineage section below for the trackline map creation process.
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 03-Jul-2006
    Ending_Date: 15-Jul-2006
    Currentness_Reference:
    Data collection interval
  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 (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 0.0000027. Longitudes are given to the nearest 0.0000027. Latitude and longitude values are specified in decimal degrees. The horizontal datum used is WGS84.
      The ellipsoid used is WGS84.
      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: Trace data are available as binary files in SEG-Y format. These files have a .SEG extension and range in size from 3 to 436 MB.
    Entity_and_Attribute_Overview:
    Graphic image file: Printable profiles are available as GIF images. Interactive profiles are available as HTML pages with accompanying JPEG images. The line navigation maps and trackline maps are JPEG images. The trackline maps contain links to the seismic profiles and line navigation maps.
    Entity_and_Attribute_Overview:
    Navigation file: Navigation files are available as ASCII text files. Provided are raw (unprocessed) shotpoint navigation files, processed shotpoint navigation files, and processed 1,000-shot-interval location files.
    Entity_and_Attribute_Overview:
    GIS file: The GIS project used to create the trackline maps is provided as a zip file composed of ESRI map documents, shapefiles, and metadata.
    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, no. 2, p. 344-352. Also available online at http://www.seg.org/publications/tech-stand.
    Entity_and_Attribute_Detail_Citation:
    Zihlman, F.N., 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, 28 p. Also available online at http://pubs.er.usgs.gov/usgspubs/ofr/ofr92590.

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Arnell S. Harrison
    • Shawn V. Dadisman
    • James G. Flocks
    • Dana S. Wiese
  2. Who also contributed to the data set?
    Funding and (or) support for this study were provided by the USGS Coastal and Marine Geology Program and the University of New Orleans. We thank R/V G.K.Gilbert captains Keith Ludwig and Dave Bennett of the USGS in St. Petersburg, FL for their assistance in data collection. This document was improved by the reviews of Dick Poore (USGS) and Amar Nayegandhi (ETI) of the USGS in St. Petersburg, FL.
  3. To whom should users address questions about the data?
    James G. Flocks
    U.S. Geological Survey
    Geologist
    600 4th Street South
    St. Petersburg, FL
    USA

    (727) 803-8747, ext. 3012 (voice)
    jflocks@usgs.gov

Why was the data set created?

The data archived here were collected as part of the USGS Barrier Island Coastal Monitoring project, which is part of a broader study focused on Subsidence and Coastal Change (SCC).

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: 2006 (process 1 of 7)
    CHIRP processing: The original trace files for lines 06c06, 06c07, 06c09, 06c10, 06c35, 06c36, 06c38, 06c48, 06c56, 06c57, 06c67, and 06c68 were divided into two or more trace files each (for example, 06c06 became 06c06_a and 06c06_b) because the original total number of traces exceeded the maximum allowed by the processing software. Line 06c31 became 06c31a because of acquistion software issues encountered during data collection, which caused a loss of data after shot 6117. The SEG-Y data were processed with Seismic Unix to produce GIF images of the seismic profiles included in this report. A representative CHIRP data processing sequence consisted of (1) stripping off channel 0 for each shot and converting to SU format, (2) applying automatic gain control, (3) displaying PostScript, and (4) converting of PostScript image to a GIF image. The processed SEG-Y data were then exported to CTI SonarWeb software to produce an interactive version of each profile that allows the user to obtain a geographic location and depth from the profile for a cursor position. Refer to the Supplemental Information section above for details on how to use the interactive profiles.
    Date: 2006 (process 2 of 7)
    SEG-Y header processing: All lines were first processed with FixPing V.1.0.0 software to correct first shot values that were other than 1 and add the year and dates, which were omitted from the trace headers. These corrected SEG-Y files are included in this archive.
    Date: 2006 (process 3 of 7)
    Navigation processing: Shotpoint navigation files and 1,000-shot-interval location files were extracted from the trace headers of each line using Seismic Unix software. To correct the lines that were missing navigation fixes from the headers, the navigation data were stripped from coincident sidescan sonar tracklines and merged with the seismic shotpoints to produce the reconstructed navigation shown on the trackline maps and in the navigation files.These files were then processed with PROJ.4 software (http://www.remotesensing.org/proj) to generate UTM coordinates from latitude and longitude coordinates and reformatted for use with Environmental Systems Research Institute (ESRI) GIS software.
    Date: 2006 (process 4 of 7)
    Trackline map creation: The trackline maps provided in this archive were created using the Points to Lines ArcScript (D. Rathert, http://arcscripts.esri.com/details.asp?dbid=12702) along with ESRI ArcGIS 9.1 software and then exported to Adobe Illustrator for further editing. The maps were later converted into JPEG format by Adobe GoLive. The maps are unprojected (geographic coordinates, NAD83). The coastline layer is a Louisiana Oil Spill Coordinator's Office (LOSCO) data set. The USGS is the originator of all other layers used. A map of trackline navigation for each seismic profile was also produced with CTI SonarWeb software.
    Date: 2006 (process 5 of 7)
    Data Series preparation: In addition to the process steps described above, the following steps were taken to produce this Data Series report: the handwritten logs were scanned and saved as PDF files, digital FACS logs were created using the handwritten 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.
    Date: 24-Jan-2017 (process 6 of 7)
    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: 13-Oct-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?

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

  1. How well have the observations been checked?
    Visual inspection of the images rendered from the data showed that intermittently during data collection, a vertical striped pattern was observed in the profiles. This anomaly was caused by an acquisition software malfunction that resulted in repetitious zero values for traces when the record length was set to less than 50 ms. The cause of the malfunction was not determined until after the cruise. Refer to figure 2 included with this archive for an illustration of this acquisition anomaly. No navigation fixes were recorded to the SEG-Y headers for tracklines 06c50 - 06c57.
  2. How accurate are the geographic locations?
    As the seismic reflection data were acquired, the position of the vessel was continuously determined by a Coda Octopus F190 receiver, which is accurate to within 20 cm. Positions were recorded and written to the trace headers in latitude and longitude coordinates about every 1 s. The ASCII navigation files and trackline maps have not been corrected to reflect the approximately 10 m offset between the CHIRP and GPS antenna. Refer to figure 1 included with this archive (Data Series XXX) for a diagram of the acquisition geometry, including the GPS offset measurements. Line navigation maps and interactive profiles generated with CTI SonarWeb software have been corrected for the GPS offset.
  3. How accurate are the heights or depths?
    These data are not to be used for bathymetry. Depths shown on the CHIRP profiles are relative to the depth of the towfish, not to sea level. Furthermore, the raising or lowering of the towfish during a survey (to avoid obstacles or follow relief) produces a relative shift in the multiple reflections seen in the profile, which may be confused as a geologic feature. Any elevation change of the towfish is recorded in the logbooks and is evident on the seismic profiles by steep, abrupt shifts in the seafloor return.
  4. Where are the gaps in the data? What is missing?
    These data are collected along tracklines (2-D) and are therefore inherently incomplete. Geologic details between lines must be inferred.
  5. How consistent are the relationships among the observations, including topology?
    This data set is from one cruise 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)
    Shawn Dadisman
    U.S. Geological Survey
    Geologist
    600 4th Street South
    St. Petersburg, FL
    USA

    (727) 803-8747, ext. 3029 (voice)
    sdadisman@usgs.gov
    Contact_Instructions:
    Data may be available on-line only by special arrangement with the distributor above.
  2. What's the catalog number I need to order this data set? U.S. Geological Survey Data Series XXX
  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 have been 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, or for general or scientific purposes, 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 standard format (Barry and others, 1975) 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 Size: 8250
      Network links: http://cmgds.marine.usgs.gov/data/06scc02/
      Media you can order: DVD (format ISO 9660)
      Note: UNIX, Linux, DOS, Macintosh
      Data format: The GIS project used to create the trackline maps is composed of map documents, shapefiles, and metadata. Map documents were created with ESRI ArcGIS 9.1 software. The shapefiles provided may also be viewed using other versions of ArcView, ArcGIS, or public domain software ArcExplorer (http://www.esri.com/software/arcexplorer/index.html). in format map document, shapefile, metadata Size: 43.9
      Media you can order: DVD (format ISO 9660)
      Note: UNIX, Linux, DOS, Macintosh
    • Cost to order the data: 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: 13-Oct-2020
Metadata author:
Arnell Harrison
ETI, contracted by U.S. Geological Survey
Geologist
600 4th Street South
St. Petersburg, FL
USA

(727) 803-8747, ext. 3111 (voice)
aharrison@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/spcmsc/DS-310.faq.html>
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