Archive of Chirp Sub-Bottom Profile, Imagery, and Navigational Data Collected During USGS Field Activity Number 2024-310-FA in 2024 from Wallops and Assawoman Islands, Virginia

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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 Number 2024-310-FA in 2024 from Wallops and Assawoman Islands, Virginia
Abstract:
In June 2024, the U.S. Geological Survey (USGS) conducted a nearshore geologic assessment, including bathymetric mapping, near Wallops and Assawoman Islands, Virginia (VA). This work was performed to collect bathymetry to initialize hydrodynamic models and acquire new sub-bottom profile data to connect with existing USGS offshore lines collected along the Delmarva Peninsula, Maryland and VA, in 2015 (Sweeney and others, 2015). These newly acquired datasets will be used to help evaluate impacts of shoreface engineering activities on system ecogeomorphology. Geophysical data were collected as part of the USGS Interconnected Coastal Environments at Decadal Timescales and Coastal Sediment Availability and Flux (CSAF) projects; more information about the CSAF project can be found at https://usgs.gov/csaf. 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, every 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., 20250318, Archive of Chirp Sub-Bottom Profile, Imagery, and Navigational Data Collected During USGS Field Activity Number 2024-310-FA in 2024 from Wallops and Assawoman Islands, Virginia:.

    This is part of the following larger work.

    Forde, Arnell S., Stalk, Chelsea A., Ciarletta, Daniel J., and Miselis, Jennifer L., 20250318, Chirp Sub-Bottom Profile Geophysical Data Collected in 2024 From Wallops Island and Assawoman Island, Virginia: U.S. Geological Survey data release doi:10.5066/P1NZ6CC2, 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: -75.531739
    East_Bounding_Coordinate: -75.400892
    North_Bounding_Coordinate: 37.864244
    South_Bounding_Coordinate: 37.755383
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 01-Jun-2024
    Ending_Date: 12-Jun-2024
    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 0.0197577306. Longitudes are given to the nearest 0.0248912658. 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 (2024-310-FA_nav.zip): Navigation files are available as ASCII delimited text files in comma-separated values file format. The survey shotpoint navigation files, 2024-310-FA_nav.csv (269,386 data records), represent the reprojected survey shotpoint navigation; 2024-310-FA_1000sht.csv (1270 data records) provides 1,000-shot-interval locations; and 2024-310-FA_sol.csv (149 data records) contains start of line information. The shapefile version of these data is available in 2024-310-FA_gis.zip. For more information about these geospatial files, refer to the 2024-310-FA_geospatial_metadata file 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 (2024-310-FA_segy.zip): Seismic trace data are available as binary files in SEG-Y format (149 files). These files have a .sgy extension and range in size from 6.2 to 230 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 (2024-310-FA_seisimag.zip): Printable versions of the processed sub-bottom profiles are available as GIF images (149 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 was provided by the USGS Coastal and Marine Hazards and Resources Program and National Aeronautics and Space Administration. The authors thank Captain Andrew Farmer of the USGS St. Petersburg Coastal and Marine Science Center (SPCMSC) for his assistance in data collection and piloting the Research Vessel (R/V) Sallenger. Field activity planning was performed by Daniel Ciarletta and Jennifer Miselis; data collection conducted by Chelsea Stalk, Jennifer Miselis, and Daniel Ciarletta; and data processing performed by Arnell Forde. This document was improved by scientific/editorial and metadata reviews from Noreen Buster and Tess Rivenbark-Terrano 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) 2024-310-FA. Additional survey and data details are available from the USGS Coastal and Marine Geoscience Data System (CMGDS) at https://cmgds.marine.usgs.gov/services/activity.php?fan=2024-310-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: 12-Jun-2024 (process 1 of 3)
    Chirp acquisition - Sub-bottom data were acquired using an Edgetech 3400 Portable Sub-Bottom Profiler (SBP), which was towed by the 26-foot research vessel, the R/V Sallenger. A total of 149 lines were surveyed. The seismic source utilized during 2024-310-FA consisted of an EdgeTech 3400 towfish running DISCOVER version 42.0.1.115 acquisition software and towed on the port side of the vessel, approximately 4 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 1-26 kilohertz (kHz) and 3-8 kHz, pulse lengths of 5 ms and 20 ms, and the recording length was 78.08 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 FACS logs and acquisition geometry figure are also provided as supplemental information in the download file, 2024-310-FA_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: 24-Jun-2024 (process 2 of 3)
    Chirp processing and image creation - The EdgeTech 3400 dual frequency SBP system recorded the sub-bottom data in JSF and SEG-Y rev. 1 formats. SEG-Y data were saved (with alternating pings supplied by each transducer) as separate files for the 1-26 kHz and 3-8 kHz frequencies. 3-8 kHz data have “A” appended to the end of the file name, for example, 153_0033_1257A.sgy. The raw JSF and SEG-Y data are not provided in the data release but are available by request. Using the jsf2segy software package (https://github.com/Geosvy/jsf2segy), JSF files were converted to analytic and envelope SEG-Y traces. The envelope SEG-Y files are comprised of the combined frequency data. This step was performed to make the data more accessible for users and reduce the quantity and total size of files being provided in this publication. 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) creating the envelope seismic data file from the analytic data (envelope converted files included in this publication have "_env" appended to the line name), (2) removing raw [vessel] navigation data for each shot and converting the SEG-Y file to SU format, (3) 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, (4) trimming the trace data TWT to 30 ms (no observable features, aside from multiples, were encountered below that point in the profiles), (5) generating a PostScript image of the traces, and (6) 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. 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: 24-Jun-2024 (process 3 of 3)
    Navigation acquisition and processing - A Teledyne T50-P multibeam system with an integrated Applanix Pos MV Wavemaster II V5 IANS with two Trimble GA830 global navigation satellite system antennas (positioned amidships) and an associated IMU was 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 Applanix receiver 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) 2024-310-FA_nav.csv contains unique shotpoint positions (along each line) for the entire survey – roughly every 5 shots, (2) 2024-310-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) 2024-310-FA_sol.csv has 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 2024-310-FA_geospatial_metadata file 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:
    • 2024-310-FA_nav.csv
    • 2024-310-FA_1000sht.csv
    • 2024-310-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:

    Sweeney, E.M., Pendleton, E.A., Ackerman, S.D., Andrews, B.D., Baldwin, W.E., Danforth, W.W., Foster, D.S., Thieler, E.R., and Brothers, L.L., 2015, High-resolution geophysical data collected along the Delmarva Peninsula 2015, U.S. Geological Survey Field Activity 2015-001-FA (ver. 3.0, May 2016): U.S. Geological Survey data release doi:10.5066/F7P55KK3, U.S. Geological Survey - Woods Hole Coastal and Marine Science Center, Woods Hole, Massachusetts.

    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® 2023 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 and were subsequently converted to decimal degrees latitude and longitude coordinates (World Geodetic System of 1984, WGS84, realization G1150). The approximate 4-m offset between the chirp shot position and the vessel's IANS reference point of the Applanix system, the Inertial Measurement Unit (IMU), 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 149 seismic lines were collected during this field activity. 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, 2024-310-FA_logs.zip.
  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 acquired during a single survey, 2024-310-FA, which occurred between June 1 and 12, 2024.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints No access constraints. Please see 'Distribution Information' for details.
Use_Constraints These data are marked with a Creative Common CC0 1.0 Universal License. These data are in the public domain and do not have any use constraints. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations.
  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? 2024-310-FA_nav.csv, 2024-310-FA_1000sht.csv, 2024-310-FA_sol.csv, *.sgy, *.gif, DataDictionary_SBP.docx
  3. What legal disclaimers am I supposed to read?
    Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. Any use of trade, firm, or product 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?
    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: 18-Mar-2025
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/2024-310-FA_seismic_metadata.faq.html>
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