Archive of Chirp Sub-Bottom Profile, Imagery, and Navigational Data Collected During USGS Field Activity Numbers 2021-326-FA and 2022-326-FA in 2021 and 2022 from Duck, North Carolina

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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 During USGS Field Activity Numbers 2021-326-FA and 2022-326-FA in 2021 and 2022 from Duck, North Carolina
Abstract:
In June/December 2021 and July 2022, the U.S. Geological Survey (USGS) and U.S. Army Corps of Engineers, Engineer Research and Development Center (USACE-ERDC) conducted repeat, nearshore geologic assessments, including bathymetric mapping, near Duck, North Carolina (NC). This work was performed in support of efforts to map the shoreface, characterize stratigraphy, and investigate changes in seafloor elevations near the USACE Field Research Facility and to measure the co-evolution of the morphology and geology of the shoreface before/after a storm and during recovery. Geophysical data were collected as part of the USGS Coastal Sediment Availability and Flux and DUring Nearshore Event eXperiment (DUNEX) projects. 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., 20240708, Archive of Chirp Sub-Bottom Profile, Imagery, and Navigational Data Collected During USGS Field Activity Numbers 2021-326-FA and 2022-326-FA in 2021 and 2022 from Duck, North Carolina:.

    This is part of the following larger work.

    Forde, Arnell S., Miselis, Jennifer L., Conery, Ian, DeWitt, Nancy T., and Buster, Noreen A., 20240708, Chirp Sub-Bottom Profile Geophysical Data Collected in 2021 and 2022 From Duck, North Carolina: U.S. Geological Survey data release doi:10.5066/P1346BEP, 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: -75.753303
    East_Bounding_Coordinate: -75.728878
    North_Bounding_Coordinate: 36.195403
    South_Bounding_Coordinate: 36.182639
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 17-Jun-2021
    Ending_Date: 13-Jul-2022
    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 0.0197644711. Longitudes are given to the nearest 0.0243727771. 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 (DUNEX_nav.zip): Navigation files are available as ASCII delimited text files in comma-separated values file format, organized into individual sub-folders per FAN. The survey shotpoint navigation files, 2021-326-FA_nav.csv (168,858 data records) and 2022-326-FA_nav.csv (72,218 data records), represent the reprojected survey shotpoint navigation; 2021-326-FA_1000sht.csv (151 data records) and 2022-326-FA_1000sht.csv (65 data records) provide 1,000-shot-interval locations; and 2021-326-FA_sol.csv (44 data records) and 2022-326-FA_sol.csv (16 data records) contain start of line information. The shapefile version of these data is available in DUNEX_gis.zip. For more information about these geospatial files, refer to the DUNEX_geospatial_metadata files included in this data release. The navigation and geospatial files mainly share the same attribute labels and definitions, aside from "FID" and "Shape", which are specific to the .shp files. Due to ArcGIS Pro character restrictions, the point shapefile attribute labels (for date and time) were changed to “DOY_HR_MIN” within the attribute tables. 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 (DUNEX_segy.zip): Seismic trace data are available as binary files in SEG-Y format (60 files), organized into individual sub-folders per FAN. These files have a .sgy extension and range in size from 1.3 to 31 megabytes. The SEG-Y rev. 1 format (Norris and Faichney, 2002) data presented here consist 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 (DUNEX_seisimag.zip): Printable versions of the processed sub-bottom profiles are available as GIF images (60 files), organized into individual sub-folders per FAN.
    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 was provided by the USGS Coastal and Marine Hazards and Resources Program and the USACE-ERDC, who provided the Lighter Amphibious Resupply Cargo (LARC) amphibious vehicle/survey vessel, personnel to pilot the vessel, geophysical and bathymetry equipment to conduct this survey, and personnel to operate the survey equipment. Field activity planning was performed by Jennifer Miselis and Noreen Buster (USGS) in collaboration with Ian Conery (USACE-ERDC); data collection conducted by Andrew Farmer, Nancy DeWitt, John (Rob) Mitchell (USACE-ERDC), and Jason Pipes (USACE-ERDC); and data processing performed by Arnell Forde. This document was improved by scientific/editorial and metadata reviews from Wayne Baldwin (WHCMSC) 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 Numbers (FANs) 2021-326-FA and 2022-326-FA. 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=2021-326-FA and https://cmgds.marine.usgs.gov/fan_info.php?fan=2022-326-FA. More information about the DUNEX project can be found at, https://www.usgs.gov/centers/whcmsc/science/usgs-dunex-operations-outer-banks.

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: 13-Jul-2022 (process 1 of 3)
    Chirp acquisition - Sub-bottom data were acquired from one survey platform that utilized an EdgeTech 512i portable sub-bottom profiling (SBP) system. The seismic system was towed on the starboard side of the 35-foot research vessel, the USACE LARC, in a catamaran sled so the transducers were 0.91 m below the water’s surface. The vessel and towing configuration allowed seismic data to be collected in < 0.5 m water depth and up the lower beach face (Locker and others, 2017). In total, 60 lines were surveyed. The seismic source utilized during the DUNEX surveys consisted of an EdgeTech 512i towfish running Chesapeake Technology SonarWiz version 5.05 acquisition software and towed on the starboard side and aft of the RTK-GPS antenna (acquisition_gps.tif; fig. 4, Locker and others (2017). The data were acquired in SEG-Y format at 5 hertz (Hz), which equates to one ping per 0.20 seconds. The frequency sweep was 0.7-12 kHz, pulse length 20 ms, and recording length was 46.5 ms. Based on survey speeds of 3.5-4.5 knots, the shot spacing was roughly 0.450 m. During acquisition, positions from the antenna 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, IEEE 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, DUNEX_logs.zip. Person who carried out this activity:
    Jennifer L. Miselis
    U.S. Geological Survey
    Research Geologist
    600 4th Street South
    St. Petersburg, FL

    (727) 502-8000 (voice)
    jmiselis@usgs.gov
    Date: 18-Mar-2024 (process 2 of 3)
    Chirp processing and image creation - The EdgeTech 512i system recorded the sub-bottom data in SEG-Y rev. 1 format. 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) setting the initial FFID value (trace header bytes 9-12) to one before incrementally increasing it by 1 and then applying automatic gain control to the profile, (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 1000 shots. Shot numbers shown on the sub-bottom profile images correspond to the trace sequence number within the line (trace header bytes 1-4) or trace sequence number within the reel (bytes 5-8) included in the SEG-Y headers for each profile. 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: 13-Jul-2022 (process 3 of 3)
    Navigation acquisition and processing - A RTK-GPS utilizing a base/rover setup was used for positioning onboard the USACE LARC. Real-time positions from the RTK-GPS were recorded and written to the seismic trace headers 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 Seismic Unix (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 18 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 in GIS software. The final output files are as follows: (1) 2021-326-FA_nav.csv and 2022-326-FA_nav.csv contain unique shotpoint positions (along each line) for the entire survey – roughly every 5 shots, (2) 2021-326-FA_1000sht.csv and 2022-326-FA_1000sht.csv include 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) 2021-326-FA_sol.csv and 2022-326-FA_sol.csv have the start-of-line locations for each trackline. The concatenated, comma-delimited text files were later imported into ArcGIS Pro 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 DUNEX_geospatial_metadata files included in this 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:
    • 2021-326-FA_nav.csv
    • 2021-326-FA_1000sht.csv
    • 2021-326-FA_sol.csv
    • 2022-326-FA_nav.csv
    • 2022-326-FA_1000sht.csv
    • 2022-326-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:

    Locker, S.D., Miselis, J.L., Buster, N.A., Hapke, C.J., Wadman, H.M., McNinch, J.E., Forde, A.S., and Stalk, C.A., 2017, Nearshore sediment thickness, Fire Island, New York: U.S. Geological Survey Open-File Report 2017–1024, U.S. Geological Survey, Reston, Virginia.

    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 a Real-Time Kinematic Global Positioning System (RTK-GPS) utilizing a base/rover setup, which is accurate to within 2 centimeters. To ensure consistent spacing between survey lines acquired aboard the USACE's LARC, pre-determined trackline locations were imported into HYPACK® 20.0.8.0 navigation software and followed during seismic data collection. During acquisition, positions from the RTK-GPS were recorded and written to the seismic trace headers in arcseconds every 0.20 s and were subsequently converted to decimal degrees latitude and longitude coordinates (World Geodetic System of 1984, WGS84, realization G1150). The approximate 1-m offset between the chirp shot position and the vessel's RTK-GPS antenna was 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 60 seismic lines were collected during these field activities. Additional survey and data details are available from the Field Activity Collection System (FACS) logs and acquisition geometry figure, which are included as supplemental information in the download file, DUNEX_logs.zip.
  5. How consistent are the relationships among the observations, including topology?
    These datasets are from three field activities with consistent instrument calibrations. Seismic data were collected during two FANs, which occurred on June 17-18 and December 3-10 of 2021 (2021-326-FA) and July 12-13, 2022 (2022-326-FA).

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? 2021-326-FA_nav.csv, 2021-326-FA_1000sht.csv, 2021-326-FA_sol.csv, 2022-326-FA_nav.csv, 2022-326-FA_1000sht.csv, 2022-326-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: 17-Jun-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/DUNEX_seismic_metadata.faq.html>
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