Archive of Chirp Sub-Bottom Profile, Imagery, and Navigational Data Collected in June and August 2023 from the Chandeleur Islands, Louisiana

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Frequently anticipated questions:

What does this data set describe?

Title:
Archive of Chirp Sub-Bottom Profile, Imagery, and Navigational Data Collected in June and August 2023 from the Chandeleur Islands, Louisiana
Abstract:
As part of the 2022 Disaster Supplemental project, scientists from the U.S. Geological Survey (USGS) St. Petersburg Coastal and Marine Science Center (SPCMSC) conducted a nearshore geophysical survey to map the shoreface and inner shelf, as well as characterize stratigraphy near the Chandeleur Islands, Louisiana (LA) in June and August 2023. The purpose of this study was to conduct a morphologic and geologic assessment of the impacts of the 2020 and 2021 hurricane seasons within part of the Breton National Wildlife Refuge (specifically around Hewes Point and Monkey Bayou). These geophysical data will be used to quantify sediment redistribution resulting from storms. The data release associated with this metadata record serves as an archive of high-resolution chirp sub-bottom trace data and navigation files. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y revision 1 format (Norris and Faichney, 2002). Processed sub-bottom profile images, survey trackline map, geographic information system (GIS) data, and formal Federal Geographic Data Committee (FGDC) Content Standard for Digital Geospatial Metadata (CSDGM) are also provided.
Supplemental_Information:
Chirp systems use a signal of continuously varying frequency; the system used during this survey produces high-resolution, shallow-penetration (typically less than 75-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, energy is reflected toward the transducer, received, and recorded by a PC-based seismic acquisition system. This process is repeated at regular 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 (2D) image of the shallow geologic structure beneath the towfish is produced.
  1. How might this data set be cited?
    Forde, Arnell S., 20240515, Archive of Chirp Sub-Bottom Profile, Imagery, and Navigational Data Collected in June and August 2023 from the Chandeleur Islands, Louisiana:.

    This is part of the following larger work.

    Forde, Arnell S., Miselis, Jennifer L., Stalk, Chelsea A., and Buster, Noreen A., 20240515, Chirp Sub-Bottom Profile Geophysical Data Collected in 2023 From the Chandeleur Islands, Louisiana: U.S. Geological Survey data release doi:10.5066/P1HOLGKM, U.S. Geological Survey - St. Petersburg Coastal and Marine Science Center, St. Petersburg, Florida.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -88.89780
    East_Bounding_Coordinate: -88.83650
    North_Bounding_Coordinate: 30.07260
    South_Bounding_Coordinate: 29.73750
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 17-Jun-2023
    Ending_Date: 08-Aug-2023
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: SEG-Y, tabular, and 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 Point data set.
    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 0.0197889864. Longitudes are given to the nearest 0.0227019979. Latitude and longitude values are specified in Decimal Degrees. The horizontal datum used is WGS_1984.
      The ellipsoid used is WGS_84.
      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?
    Entity_and_Attribute_Overview:
    Navigation files (2023-325-FA_nav.zip): Navigation files are available as ASCII delimited text files in comma-separated values file format. The survey's shotpoint navigation file, 2023-325-FA_nav.csv (78,038 data records), represents the reprojected survey shotpoint navigation; 2023-325-FA_1000sht.csv (369 data records) provides 1,000-shot-interval locations; and 2023-325-FA_sol.csv (40 data records) contains start of line information. The shapefile version of these data is available in 2023-325-FA_gis.zip. For more information about these geospatial files, refer to the 2023-325-FA_geospatial_metadata files included in the data release. The navigation and geospatial files share the same attribute labels and definitions, aside from "FID" and "Shape", which are specific to the .shp files. The detailed attribute descriptions for the navigation files are provided in the data dictionary (DataDictionary_SBP.docx), the metadata are not complete without this file.
    Entity_and_Attribute_Overview:
    Binary data files (2023-325-FA_segy.zip): Seismic trace data are available as binary files in SEG-Y format (40 files). These files have a .sgy extension and range in size from 10.3 to 254.5 megabytes. The SEG-Y rev. 1 format (Norris and Faichney, 2002) data 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.
    Entity_and_Attribute_Overview:
    Graphic image files (2023-325-FA_seisimag.zip): Printable versions of the processed sub-bottom profiles are available as GIF images (40 files).
    Entity_and_Attribute_Detail_Citation:
    The entity and attribute information were generated by the individual or agency identified as the originator of the dataset. Please review the rest of the metadata record for additional details and information.

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
  2. Who also contributed to the data set?
    Funding and (or) support for this study were provided by the Department of Interior Supplemental Appropriations for Disaster Recovery Activities Task 1, part of the Extending Government Funding and Delivering Emergency Assistance Act (Public Law 117-43) and the USGS Coastal and Marine Hazards and Resources Program. The authors thank Andrew Farmer of SPCMSC for his assistance with data collection and piloting the Research Vessel (R/V) Sallenger. Field activity planning was performed by Noreen Buster and Jennifer Miselis; data collection conducted by Chelsea Stalk and Jennifer Miselis; and data processing performed by Arnell Forde. This document was improved by scientific/editorial and metadata reviews from Nancy DeWitt and Breanna Williams of the SPCMSC.
  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) 502-8000 (voice)
    aforde@usgs.gov

Why was the data set created?

The purpose of the data release described herein is to archive and disseminate digital chirp sub-bottom profile data and associated files collected during USGS Field Activity Number (FAN) 2023-325-FA (subFANs 23BIM05 and 23BIM10). Additional survey and data details are available from the USGS Coastal and Marine Geoscience Data System (CMGDS) at, https://cmgds.marine.usgs.gov/fan_info.php?fan=2023-325-FA.

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: 08-Aug-2023 (process 1 of 3)
    Chirp acquisition - Sub-bottom data were acquired from one survey platform that utilized two, different EdgeTech portable sub-bottom profiling (SBP) systems. EdgeTech's 3100-P (aka chirp SB-424; frequency range from 4-24 kilohertz (kHz)) and 3400 (aka chirp SB-216; dual frequency 2-16 kHz transducers) SBPs were towed on the port side of the 26-foot research vessel, the R/V Sallenger. In total, 40 lines, equivalent to a total of 135.1 line-kilometers, were surveyed. The seismic source utilized during 2023-325-FA consisted of an EdgeTech 424 or 216 towfish running DISCOVER version 4.09 acquisition software and towed on the port side of the vessel, 3.56 m across-track from the IANS reference point. The data were acquired in J-STAR standard format (JSF) and SEG-Y format at 5 hertz (Hz), which equates to one ping per 0.20 seconds. The frequency sweep was 4-20 kHz (DOY 217); 3-12 kHz (DOY 219 and 220); or 3-16 kHz (DOY 168), pulse lengths ranged between 5 ms and 20 ms, and recording lengths were 35.5 ms (DOY 219 and 220), 59.18 ms (DOY 168), and 60.47 ms (DOY 217). Based on survey speeds of 3.5-4.5 knots, the shot spacing was roughly 0.450 m. During acquisition, positions from the POS MV IANS were recorded and written to the seismic trace headers in arcseconds every 0.20 s. The binary portion of the seismic data provided in the data release is stored in SEG-Y rev. 1, IBM 32-bit float [big-endian byte order] 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 Extended Binary Coded Decimal Interchange Code (EBCDIC) format. The SEG-Y formatted envelope trace files have a .sgy extension and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU) (Cohen and Stockwell, 2010). The printable profiles (provided in .gif format) are chirp sub-bottom profile images that were processed using SU software. Survey Field Activity Collection System (FACS) logs and acquisition geometry figure are also provided as supplemental information in the download file, 2023-325-FA_logs.zip. Person who carried out this activity:
    Jennifer Miselis
    U.S. Geological Survey
    Research Geologist
    600 4th Street South
    St. Petersburg, FL

    (727) 502-8000 (voice)
    jmiselis@usgs.gov
    Date: 23-Jan-2024 (process 2 of 3)
    Chirp processing and image creation - The EdgeTech 3100 and 3400 chirp systems recorded the sub-bottom data in JSF and SEG-Y rev. 1 formats. Enveloped SEG-Y trace data were processed with custom scripts and SU Release 44 (Cohen and Stockwell, 2010) software to produce gained Graphics Interchange Format (GIF) images of the sub-bottom profiles included in the data release. A representative chirp data processing sequence consisted of (1) removing raw [vessel] navigation data for each shot and converting the SEG-Y file to SU format, (2) applying automatic gain control, (3) trimming the trace data TWT to 30 ms (no observable features, aside from multiples, were encountered below that point in the profiles), (4) generating a PostScript image of the traces, and (5) converting the PostScript image to a GIF image. The sub-bottom profile images have tic marks every 200 shots, with labels, larger tic marks, and dashed grid lines every 1,000 shots. Person who carried out this activity:
    Arnell S. Forde
    U.S. Geological Survey
    Geologist
    600 4th Street South
    St. Petersburg, FL

    (727) 502-8000 (voice)
    aforde@usgs.gov
    Data sources used in this process:
    • *.sgy
    Data sources produced in this process:
    • *.gif
    Date: 23-Jan-2024 (process 3 of 3)
    Navigation acquisition and processing - A Teledyne Reson T50P dual head MBES system and Applanix POS MV Wavemaster II IANS with two Trimble GA830 GNSS antennas (positioned forward-aft near the aft-starboard of the vessel) were used for positioning onboard the R/V Sallenger. Real-time positions from the Applanix system were recorded and written to the seismic trace headers via a RS232 cable running from the antenna to the topside unit of the chirp system every 0.20 seconds, with unique navigation fixes being recorded every second. During sub-bottom processing, location data were extracted from the SEG-Y headers of the processed chirp profiles, using bespoke scripts and SU (Cohen and Stockwell, 2010) software and output as ASCII text files; PROJ.5.1.0 (https://proj.org/) software was used to project WGS84 latitude and longitude coordinates to Universal Transverse Mercator (UTM) northings and eastings (WGS84, Zone 16 North (N), meters). Navigation files for each sub-bottom line, saved by line number, were concatenated into comma-separated values (.csv) files so they could be represented geospatially using GIS software. The final output files are as follows: (1) 2023-325-FA_nav.csv contains unique shotpoint positions (along each line) for the entire survey – roughly every 5 shots, (2) 2023-325-FA_1000sht.csv includes the 1,000-shot-interval locations that were generated to correlate shot locations along the tracklines with evenly spaced 1,000-shot index markers along the top of the printable profile images, and (3) 2023-325-FA_sol.csv has the start-of-line locations for each trackline. The concatenated, comma-delimited text files were later imported into ArcMap and saved as either a point or polyline file (in Esri's shapefile format, .shp) for subsequent use in GIS software packages. For more information about these geospatial files, refer to the 2023-325-FA_geospatial_metadata files included in the data release. Person who carried out this activity:
    Arnell S. Forde
    U.S. Geological Survey
    Geologist
    600 4th Street South
    St. Petersburg, FL

    (727) 502-8000 (voice)
    aforde@usgs.gov
    Data sources used in this process:
    • *.txt
    Data sources produced in this process:
    • 2023-325-FA_nav.csv
    • 2023-325-FA_1000sht.csv
    • 2023-325-FA_sol.csv
  3. What similar or related data should the user be aware of?
    Norris, M.W., and Faichney, A.K., 2002, SEG-Y rev 1 Data Exchange format: Society of Exploration Geophysicists, SEG Technical Standards Committee Release 1.0, May 2002.

    Online Links:

    Cohen, J.K., and Stockwell, J.W., Jr., 2010, Seismic Un*x Release No. 44: An open source software package for seismic research and processing: Center for Wave Phenomena, Colorado School of Mines, Golden, Colorado.

    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 sub-bottom profiles is highly qualitative and dependent on equipment and operating condition variables.
  2. How accurate are the geographic locations?
    As the sub-bottom profile data were acquired, the position of the vessel was continuously determined by an Applanix POS MV Wavemaster II inertial aided navigation system (IANS), which is accurate to within 0.5-2 meters (m). To ensure consistent spacing between survey lines acquired aboard the R/V Sallenger, pre-determined trackline locations were imported into HYPACK 2022.3.5 navigation software and followed during seismic data collection. During acquisition, positions from the POS MV IANS were recorded and written to the seismic trace headers in arcseconds every 0.20 s (with unique navigation fixes being recorded every second) and were subsequently converted to decimal degrees latitude and longitude coordinates (World Geodetic System of 1984, WGS84, realization G1150). The approximate 3-m offset between the chirp shot position and the vessel's IANS reference point were not accounted for during acquisition, nor have the American Standard Code for Information Interchange (ASCII) navigation files and trackline map been corrected to reflect the offset.
  3. How accurate are the heights or depths?
    These data are not to be used for bathymetry or navigation. Two-way travel times (TWT) shown on the printable profile images are relative to the chirp towfish position (below the sea surface), not to the sea surface.
  4. Where are the gaps in the data? What is missing?
    A total of 40 seismic lines were collected during this field activity.
  5. How consistent are the relationships among the observations, including topology?
    These datasets are from one field activity with consistent instrument calibrations. Seismic data were collected during two surveys, which occurred on June 17 (Leg 1; subFAN 23BIM05) and August 5–8, 2023 (Leg 2; subFAN 23BIM10).

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 Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. 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)
    SPCMSC Data Management Group
    U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center
    600 4th Street South
    St. Petersburg, FL
    USA

    (727) 502-8000 (voice)
    gs-g-spcmsc_data_inquiries@usgs.gov
  2. What's the catalog number I need to order this data set? 2023-325-FA_nav.csv, 2023-325-FA_1000sht.csv, 2023-325-FA_sol.csv, *.sgy, *.gif, DataDictionary_SBP.docx
  3. What legal disclaimers am I supposed to read?
    This 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?
  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 (https://github.com/JohnWStockwellJr/SeisUnix).

Who wrote the metadata?

Dates:
Last modified: 15-May-2024
Metadata author:
SPCMSC Data Management Group
U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center
600 4th Street South
St. Petersburg, FL
USA

(727) 502-8000 (voice)
gs-g-spcmsc_data_inquiries@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/spcmsc/2023-325-FA_metadata.faq.html>
Generated by mp version 2.9.51 on Thu May 16 10:13:55 2024