Seismic Reflection, EdgeTech SB-512i chirp profile images,USGS field activity 2017-003-FA, Mississippi River Delta front offshore of southeastern Louisiana (PNG images)

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Frequently anticipated questions:

What does this data set describe?

Seismic Reflection, EdgeTech SB-512i chirp profile images,USGS field activity 2017-003-FA, Mississippi River Delta front offshore of southeastern Louisiana (PNG images)
High resolution bathymetric, sea-floor backscatter, and seismic-reflection data were collected offshore of southeastern Louisiana aboard the research vessel Point Sur on May 19-26, 2017, in an effort to characterize mudflow hazards on the Mississippi River Delta front. As the initial field program of a research cooperative between the U.S. Geological Survey, the Bureau of Ocean Energy Management, and other Federal and academic partners, the primary objective of this cruise was to assess the suitability of sea-floor mapping and shallow subsurface imaging tools in the challenging environmental conditions found across delta fronts (for example, variably distributed water column stratification and widespread biogenic gas in the shallow subsurface). Approximately 675 kilometers (km) of multibeam bathymetry and backscatter data, 420 km of towed chirp data, and 550 km of multichannel seismic data were collected. Varied mudflow (gully, lobe), prodelta morphologies, and structural features were imaged in selected survey areas from Pass a Loutre to Southwest Pass.
Additional information on the field activity is available from
  1. How might this data set be cited?
    U.S. Geological Survey, 2018, Seismic Reflection, EdgeTech SB-512i chirp profile images,USGS field activity 2017-003-FA, Mississippi River Delta front offshore of southeastern Louisiana (PNG images): data release DOI:10.5066/F7X929K6, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, Massachusetts.

    Online Links:

    This is part of the following larger work.

    Baldwin, Wayne E., Ackerman, Seth D., Worley, Charles R., Danforth, William W., and Chaytor, Jason D., 2018, High-resolution geophysical data collected along the Mississippi River Delta front offshore of southeastern Louisiana, U.S. Geological Survey Field Activity 2017-003-FA: data release DOI:10.5066/F7X929K6, U.S. Geological Survey, Reston, VA.

    Online Links:

    Suggested citation: Baldwin, W.E., Ackerman, S.D., Worley, C.R., Danforth, W.W., and Chaytor, J.D, 2018, High-resolution geophysical data collected along the Mississippi River Delta front offshore of southeastern Louisiana, U.S. Geological Survey Field Activity 2017-003-FA: U.S. Geological Survey data release,
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -89.554864
    East_Bounding_Coordinate: -88.862675
    North_Bounding_Coordinate: 29.285489
    South_Bounding_Coordinate: 28.775983
  3. What does it look like? (JPEG)
    Thumbnail image of chirp seismic-reflection profile example from the Mississippi River Delta front offshore of southeastern Louisiana.
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 21-May-2017
    Ending_Date: 24-May-2017
    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?
    The PNG seismic reflection images can be hyperlinked to their corresponding trackline or shotpoint locations in ArcGIS using the shapefiles '2017-003-FA_512i_Tracklines.shp' or '2017-003-FA_512i_500sht.shp', respectively (available from the larger work citation). The images show two-way travel time (seconds) on the y-axis and distance along profile (annotation at 500 shot intervals) on the x-axis.
    Entity_and_Attribute_Detail_Citation: U.S. Geological Survey

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?
    U.S. Geological Survey
    Attn: Wayne E. Baldwin
    384 Woods Hole Road
    Woods Hole, Massachusetts

    508-548-8700 x2226 (voice)
    508-457-2310 (FAX)

Why was the data set created?

These PNG images represent approximately 420 km of chirp seismic-reflection data collected by the U.S. Geological Survey during cruise 2017-003-FA along the Mississippi River Delta front offshore of southeastern Louisiana. Images of each seismic profile were generated in order to provide portable and easily viewable alternatives to the SEGY versions of the data. Each profile image can be hotlinked to its corresponding trackline navigation contained within the Esri polyline shapefile '2017-003-FA_512i_Tracklines.shp'. Shotpoint index marks along the top of the PNG images correlate to the positions of 500 shot intervals within the Esri point shapefile '2017-003-FA_512i_500sht.shp'.

How was the data set created?

  1. From what previous works were the data drawn?
    SEG-Y 512i data (source 1 of 1)
    U.S. Geological Survey, Unpublished Material, 512i PNG image data.

    Type_of_Source_Media: disc
    Chirp seismic data were collected using an EdgeTech Geo-Star FSSB sub-bottom profiling system and an SB-0512i towfish (0.5-12 kHz), which was mounted on a catamaran and towed astern of the R/V Point Sur of Gulfport, MS. Chesapeake Technology's SonarWiz (version 6.05.0011) seismic acquisition software was used to control the Geo-Star topside unit, digitally log trace data in the SEG-Y Rev. 1 format (IEEE floating point), and record GPS navigation coordinates to the SEG-Y trace headers (in arc seconds of Latitude and Longitude, multiplied by a scalar of 100). Data were acquired using shot rates between 250 and 750 milliseconds (ms), a 30-ms pulse length, and a 0.5 to 7.2 kHz frequency sweep. Traces were recorded with a 46-microsecond sample interval over lengths between approximately 180 and 700 ms.
  2. How were the data generated, processed, and modified?
    Date: Dec-2017 (process 1 of 2)
    Scripts within SIOSEIS (version 2015.3.1) and Seismic Unix (version 4.2) were used to process SEG-Y data, create navigation files, and plot images. The processing flow and scripts used to produce navigation files including trackline shapefiles are summarized below and in the following processing steps.
    1) SIOSEIS (version 2015.3.1) was used to read SEG-Y files, renumber shots starting from one, extract the envelope-detected trace, and write out new SEG-Y files. The original shot numbers, which were assigned by SonarWiz sequentially over the duration of an acquisition session despite SEG-Y file changes, are preserved in the raw SEG-Y data.
    2) The SIOSEIS script Sio_medianstk was used to minimize cross talk from the multichannel seismic acquisition sources (boomer and sparker) with a two-trace median stack (trim 50 percent of the values furthest from the median amplitude) and improve water bottom picking. This script was used for all lines even when multi-channel acquisition was not simultaneously occurring, due to the improvements made to water bottom picks.
    3) The script Read512i_mstk was used to read median filtered stacked and renumbered SEG-Y files, write a Seismic Unix file, and extract SEG-Y trace header information, including shot number, longitude, latitude, year, Julian day, and time of day (UTC). Header information from each SEG-Y file was saved to text files after an AWK (no version) filter was used to maintain the first and last shots, shots at multiples of 100, 500, and shots with unique navigation coordinates. Geographic coordinates (WGS 84) were converted to UTM zone 16 N coordinates (WGS 84) using Proj (version 4.6.0). End shots and shots at multiples of 100 may not have unique navigation coordinates. Separate text files containing the first and last shots and even 500 shot intervals were also saved. A 500 shot interval was chosen because it corresponds to the annotation interval provided along the top of the seismic-reflection profile images. Read512i_mstk called a Python script, written by Wayne Baldwin, which imported the CSV files to a Spatialite (version 4.3.0) enabled SQLite (version 3.21.0) database.
    4. The SIOSEIS script siothresh_pltwbt was used to pick the water-bottom time from the median stacked SEG-Y files, apply a swell filter to smooth water-bottom time picks and shift the trace data by the difference between the smoothed and unsmoothed water bottom time before writing the shifted trace data to a new SEG-Y file.
    5. The Seismic Unix script Plot512i_s creates a swell-filtered PNG image using ImageMagick (version 6.9.5-4) of each seismic line that is 12 inches high. Images show two-way travel time (seconds) along the y-axis (left margin) and shots along profile (labeled at 500 shot intervals) on the x-axis (along top of profile). Person who carried out this activity:
    Wayne E. Baldwin
    U.S. Geological Survey
    384 Woods Hole Rd.
    Woods Hole, MA

    (508) 548-8700 x2226 (voice)
    (508) 457-2310 (FAX)
    Date: 07-Aug-2020 (process 2 of 2)
    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)
  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?
  2. How accurate are the geographic locations?
    Although navigation is not stored in the images, positional accuracy is relevant to the accuracy of these data. The EdgeTech SB-0512i subbottom profiler was mounted on a catamaran sled and towed at the sea surface approximately 40 m astern of the M/V Scarlett Isabella. The transducer depth below water line was 0.5 meters below catamaran floats. Navigation data for the 512i were collected using a Wide Area Augmentation System (WAAS) enabled Garmin Differential GPS (DGPS) receiver, which was located on the catamaran sled and connected to the acquisition computer via a serial cable. Positioning data were recorded in SonarWiz (version 6.05.0011) acquisition software, which logged positioning coordinates to individual trace headers SEG-Y format. WAAS enabled GPS horizontal positional accuracy is assumed to be within 2 m; however, horizontal position uncertainty increases with sonar and sled motion, which was not compensated for at the sonar transducer.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    Sections of tracklines where navigation was recorded but no seismic data were logged are not included such as during testing, some turns, and very short files. There are no Line-0001, Line-0004, Line-0016 or Line-0017.
  5. How consistent are the relationships among the observations, including topology?
    Processed seismic data were converted to PNG format for ease of seismic trace display. Quality control was conducted during processing.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: None
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)
    U.S. Geological Survey - ScienceBase
    Federal Center
    Denver, CO

    1-888-275-8747 (voice)
  2. What's the catalog number I need to order this data set? USGS data release 2017-003-FA 512i PNG imagery from the Mississippi River Delta front area: includes the zip archive containing 55 PNG images named according to line convention with an '_s' appended to note swell-filter processing, the browse graphic 2017-003-FA_512i_Images_browse.jpg, and the Federal Geographic Data Committee (FGDC) Content Standards for Digital Geospatial Metadata (CSDGM) metadata file 2017-003-FA_512i_Images_meta.xml.
  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 can be viewed with any PNG image viewing software. The zip files must be uncompressed in order to view the images.

Who wrote the metadata?

Last modified: 07-Aug-2020
Metadata author:
U.S. Geological Survey
Attn: Wayne E. Baldwin
384 Woods Hole Rd.
Woods Hole, MA

(508) 548-8700 x2226 (voice)
(508) 457-2310 (FAX)
Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)

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