Archive of Chirp Subbottom Profile Data Collected in 2019 from Cedar Island, Virginia

Frequently anticipated questions:

• What does this data set describe?
  1. How might this data set be cited?
  2. What geographic area does the data set cover?
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
  5. What is the general form of this data set?
  6. How does the data set represent geographic features?
  7. How does the data set describe geographic features?
• Who produced the data set?
  1. Who are the originators of the data set?
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
• Why was the data set created?
• How was the data set created?
  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
  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?
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
  5. How consistent are the relationships among the data, including topology?
• How can someone get a copy of the data set?
  1. Are there legal restrictions on access or use of the data?
  2. Who distributes the data?
  3. What's the catalog number I need to order this data set?
  4. What legal disclaimers am I supposed to read?
  5. How can I download or order the data?
• Who wrote the metadata?

What does this data set describe?

1. How might this data set be cited?
   Forde, Arnell S., Stalk, Chelsea A., and Miselis, Jennifer L., 20201015, Archive of Chirp Subbottom Profile Data Collected in 2019 from Cedar Island, Virginia: U.S. Geological Survey Data Release doi:10.5066/P9S75Q0U, U.S. Geological Survey - St. Petersburg Coastal and Marine Science Center, St. Petersburg, Florida.

   Online Links:

   • https://doi.org/10.5066/P9S75Q0U

2. What geographic area does the data set cover?

   West_Bounding_Coordinate: -75.614853
   East_Bounding_Coordinate: -75.539711
   North_Bounding_Coordinate: 37.695744
   South_Bounding_Coordinate: 37.570942
   

3. What does it look like?
4. Does the data set describe conditions during a particular time period?

   Beginning_Date: 09-Aug-2019

   Ending_Date: 14-Aug-2019

   Currentness_Reference:

   ground condition

5. What is the general form of this data set?

   Geospatial_Data_Presentation_Form: Multimedia presentation
   

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. It contains the following vector data types (SDTS terminology):
      • Point (551935)
   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 0.0197584720. Longitudes are given to the nearest 0.0248328387. 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?

   2019-332-FA.txt, s2019-332-FA.txt, 2019-332-FA_s.txt

   These files, which are located in 2019-332-FA_nav.zip, represent the August 2019 seismic navigation data. The attributes described below are for the survey's shotpoint navigation file, 2019-332-FA.txt. For detailed information specific to the ArcGIS data, please see the associated shapefile metadata. (Source: SEG Y headers, https://seg.org/Publications/tech-stand.)

   UTMX

   UTM-X coordinate (Zone 18) (Source: Universal Transverse Mercator Coordinate System)

   Range of values
   Minimum:	445722.143
   Maximum:	452416.263
   Units:	meters

   UTMY

   UTM-Y coordinate (Zone 18) (Source: Universal Transverse Mercator Coordinate System)

   Range of values
   Minimum:	4158363.231
   Maximum:	4172213.632
   Units:	meters

   Line

   Trackline name (Source: U.S. Geological Survey) The naming convention used for each subbottom profile line is as follows: FAN_Line#_env_bp or FAN_Line#_env_bp_mod, where 'FAN' is the USGS field activity number assigned to the survey (without the "-FA" suffix, for example, 2019-332), 'Line#' is a number representing a specific trackline, and '_env_bp' denotes that the seismic data were bandpass filtered then output as envelope data files. Files with "_env_bp_mod" appended to the filename used post-processed DGPS coordinates for navigation, all other files used real-time kinematic positions recorded during acquisition.

   Shot

   Shotpoint number (Source: U.S. Geological Survey)

   Range of values
   Minimum:	1
   Maximum:	24511

   Lon

   Longitude (decimal degrees) (Source: World Geodetic System 1984 Geographic Coordinate System)

   Range of values
   Minimum:	-75.614853
   Maximum:	-75.539711
   Units:	decimal degrees

   Lat

   Latitude (decimal degrees) (Source: World Geodetic System 1984 Geographic Coordinate System)

   Range of values
   Minimum:	37.570942
   Maximum:	37.695744
   Units:	decimal degrees

   YEAR

   Year of data acquisition (Source: U.S. Geological Survey)

   Range of values
   Minimum:	2019
   Maximum:	2019

   DOY:HR:MIN:SEC

   Day of year:hour:minute:second (Source: U.S. Geological Survey) Day of year, hour, minute and second of data acquisition.

   Entity_and_Attribute_Overview:

   Binary data file: Seismic trace data are available as binary files in SEG Y format. These files have a .sgy extension and range in size from 4 to 480 MB. These data are included in the download file, 2019-332-FA_segy.zip, and can also be found by going to https://cmgds.marine.usgs.gov. The SEG Y rev. 0 format (Barry and others, 1975) 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 file: Printable versions of the processed subbottom profiles are available as GIF images and are included in the download file, 2019-332-FA_seisimag.zip.

   Entity_and_Attribute_Overview:

   Navigation file: Navigation files are available as ASCII text files. Provided are reprojected survey shotpoint navigation, 1,000-shot-interval locations, and start of line files. The final navigation files are provided in 2019-332-FA_nav.zip.

   Entity_and_Attribute_Overview:

   GIS file: The GIS data associated with this survey are provided as a compressed zip file, 2019-332-FA_gis.zip, which is composed of an Esri map document, shapefiles, individual shapefile metadata, a Google Earth KMZ file, a folder of processed profile images, and a readme file. The shapefiles provided may also be viewed using other versions of Esri desktop software including their free software Explorer for ArcGIS, which is available at https://www.esri.com/en-us/arcgis/products/explorer-for-arcgis.

   Entity_and_Attribute_Detail_Citation:

   The entity and attribute information were generated by the individual and/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
   • Chelsea A. Stalk
   • Jennifer L. Miselis
2. Who also contributed to the data set?

   Funding and (or) support for this study were provided by the USGS Coastal and Marine Hazards and Resources Program. The authors thank Andrew Farmer of the USGS for his assistance in data collection and piloting the R/V Sallenger. This document was improved by scientific/editorial and metadata reviews from Daniel Ciarletta and Breanna Williams of the USGS - St. Petersburg, Florida.

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 this data release is to facilitate the archive of digital chirp subbottom profile data and associated files collected during USGS Field Activity Number 2019-332-FA. Additional survey and data details are available from the USGS CMGDS at, https://cmgds.marine.usgs.gov/fan_info.php?fan=2019-332-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: 25-Feb-2020 (process 1 of 4)

   Chirp acquisition and processing - USGS scientists created a purpose-built, towed sled system to mount the 512i chirp subbottom profiler (just below the water's surface) and enable launching and recovery from the beach. The seismic sled was also configured to help ensure the quality of data collected in exceedingly shallow water depths, such as those observed near the shoreline, over shallow nearshore bars, and within the surf zone. Subbottom data were acquired from one survey platform, the seismic sled, which was towed by the 26-foot R/V Sallenger. 64 lines, equivalent to a total of 299.075 line-kilometers, were surveyed. The SEG Y data were processed with Seismic Unix (Release 44) software to produce gained Graphics Interchange Format (GIF) images of the subbottom profiles included in this data release. A representative chirp data processing sequence consisted of (1) applying a 3000-4000-10,000-12,000 bandpass filter to the analytic data to remove noise from the raw data, prior to creating the envelope seismic data file; corrected files included in this publication have "_env_bp" appended to the line name (2) removing raw navigation data for each shot and converting the SEG Y file to SU format, (3) inserting post-processed DGPS coordinates into the headers, these files have "_env_bp_mod" appended to file name (4) applying automatic gain control, (5) generating a PostScript image of the traces, and (6) converting the PostScript image to a GIF image. 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:

   • SEG Y

   Data sources produced in this process:

   • SEG Y.gif

   Date: 29-Jul-2020 (process 2 of 4)

   Navigation acquisition and processing: An Ashtech Proflex 800 unit with a global navigation satellite system antenna (positioned amidships) was used for positioning onboard the R/V Sallenger. Real-time positions from the Proflex were recorded and written to the seismic trace headers via a RS232 cable running from the Proflex receiver to the topside unit of the chirp system. Supplementary acquisition and processing information for the navigation data associated with the seismic sled and GPS are included in Cedar_Island_2019_SBES_metadata.txt (Stalk and others, 2020). Location data were extracted from the SEG Y headers of the processed subbottom profiles, using Seismic Unix software and output as ASCII text files; PROJ.5.1.0 (https://proj4.org/) software was used to project WGS84 latitude and longitude coordinates to Universal Transverse Mercator (UTM) northings and eastings (WGS84, Zone 18, meters). Navigation files for each seismic line, saved by line number, were concatenated into comma-delimited text files for use with Esri ArcGIS software. The final output files are as follows: (1) 2019-332-FA.txt contains unique shotpoint positions (along each line) for the entire survey, (2) s2019-332-FA.txt includes the 1,000-shot-interval locations that were generated to correlate shot locations on the trackline map with evenly spaced 1,000-shot index markers along the top of the printable profile images, and (3) 2019-332-FA_s has the start-of-line locations for each trackline. The concatenated, comma-delimited text files were later imported into ArcGIS and saved as either a point or polyline file (in Esri's shapefile format) for use in the map document (.mxd) included in this archive. 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:

   • *_env_bp.txt, *_env_bp_mod.txt

   Data sources produced in this process:

   • 2019-332-FA.txt
   • s2019-332-FA.txt
   • 2019-332-FA_s.txt

   Date: 29-Jul-2020 (process 3 of 4)

   Trackline map creation: 2019-332-FA_location.mxd and associated shapefiles (.shp) were created with Esri ArcGIS 10.6 software. The survey navigation file, 2019-332-FA.txt, was imported into ArcMap 10.6.0.8321 and processed using the ArcScript "Points to Lines" to create a polyline shapefile of the cruise tracklines called 2019-332-FA_trkln. The 1,000-shot-interval and start-of-line files, s2019-332-FA.txt and 2019-332-FA_s.txt, were imported into ArcMap and saved as point shapefiles. A non-proprietary version of the location map was created by utilizing the ArcToolbox "Map to KML" tool, which converted each layer included in the .mxd document to keyhole markup language (.kml) format prior to them being compressed and saved as a .kmz file. The ArcGIS and Google Earth geospatial files provided in this data release are unprojected (geographic coordinates, WGS84). For detailed information about the ArcGIS files provided in this data release, please refer to the individual metadata records (*_metadata.txt and *.shp.xml) accompanying each shapefile and the readme file included in 2019-332-FA_gis.zip. 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:

   • 2019-332-FA.txt
   • s2019-332-FA.txt
   • 2019-332-FA_s.txt

   Data sources produced in this process:

   • 2019-332-FA_trkln.shp
   • 2019-332-FA_shots.shp
   • 2019-332-FA_sol.shp
   • 2019-332-FA.kmz

   Date: 10-Nov-2020 (process 4 of 4)

   Added keywords section with USGS persistent identifier as theme keyword. Person who carried out this activity:
   

   U.S. Geological Survey

   Attn: Arnell S. Forde

   Geologist

   600 4th Street South

   St. Petersburg, FL
   

   (727) 502-8000 (voice)

   aforde@usgs.gov

3. What similar or related data should the user be aware of?
   Barry, K.M., Cavers, D.A., and Kneale, C.W., 1975, Recommended standards for digital tape formats: Geophysics v. 40, no. 2.

   Online Links:

   • https://doi.org/10.1190/1.1440530

   Other_Citation_Details: pages 344-352
   

   Cohen, J.K., and Stockwell, J.W., Jr., CWP/SU, 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:

   • https://github.com/JohnWStockwellJr/SeisUnix

   Stalk, C.A., Farmer, A.S., and Miselis, J.L., 20201005, Coastal Single-beam Bathymetry Data Collected in September 2019 from Cedar Island, Virginia: U.S. Geological Survey Data Release doi:10.5066/P927Q8M1, U.S. Geological Survey - St. Petersburg Coastal and Marine Science Center, St. Petersburg, Florida.

   Online Links:

   • https://doi.org/10.5066/P927Q8M1

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 subbottom profiles is highly qualitative and dependent on equipment and operating condition variables. Due to a problem with the acquisition computer's clock, the wrong day of year (DOY) was recorded to the SEG Y files acquired in the field; however, the correct DOY was recorded to the [proprietary] JSTAR Standard Format (JSF) files (.jsf) that were saved concurrently along with the SEG Y files. To correct this issue, the .jsf files were converted to .sgy format and subsequently used during subbottom processing. During preliminary chirp data processing, visual inspection of the images rendered from the subbottom data showed the presence of an anomaly at approximately 10 ms (two-way travel time [TWT]) on some profiles. This issue was resolved during post-processing and the data were re-checked for quality assurance/quality control compliance. Various equipment issues (for example, GPS or battery) were encountered during data collection; consequently, if post-processed navigation were unavailable for a line, real-time kinematic (RTK) navigation was used instead. Chirp lines with "_env_bp_mod" appended to the file name used post-processed differential global positioning system (DGPS) coordinates for navigation, all other lines used RTK positions recorded during acquisition.
2. How accurate are the geographic locations?
   Both subbottom and bathymetry data were collected aboard a towed seismic sled, which was outfitted with a GPS receiver and single-beam echosounder. An Ashtech Proflex 800 GPS receiver was used to collect position information on the sled. Differential positioning was obtained through post-processing the base station (established on National Geodetic Survey benchmark AJ4587) data to the rover located on the sled. Manufacture stated accuracy for positioning utilizing a DGPS is 0.5-2 m. To ensure consistent spacing between survey lines (for example, 5 m in the nearshore and 10 m for offshore lines), a similar GPS set up was established aboard the R/V Sallenger, where pre-determined trackline locations were imported into HYPACK 2018 navigation software and followed during seismic data collection. Positions from the Proflex receiver located on the R/V Sallenger were recorded and written to seismic trace headers in arcseconds every 1 second (s) and were subsequently converted to latitude and longitude coordinates (World Geodetic System of 1984, WGS84, realization G1762). The approximate 18-m offset between the chirp shot/sled position and ship's GPS antenna reference point were not accounted for during acquisition. For additional positional accuracy and navigation details specific to the GPS and bathymetry data, please refer to the metadata included in Stalk and others (2020).
3. How accurate are the heights or depths?
   These data are not to be used for bathymetry. TWT times shown on the printable profile images are relative to the chirp towfish position, not to the sea surface.
4. Where are the gaps in the data? What is missing?
   A total of 64 seismic lines were collected during this field activity. 11 tracklines had none or partial post-processed navigation. On DOY 222, only the JSF file for line 0002_1416 was recorded in the field, the .sgy file provided in this data release was created during seismic post-processing. The last line collected on DOY 223, 0016_1939, ended prematurely because of battery failure. Due to poor weather conditions, no data were collected on DOY 225 of this survey. Please see the "Corrections" tab of 2019_332_CHIRP_SBES_OpsLog.xlsx for detailed descriptions of changes made during seismic processing.
5. How consistent are the relationships among the observations, including topology?
   These datasets are from one field activity 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:

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)
   
   Arnell S. Forde

   U.S. Geological Survey

   Geologist

   600 4th Street South

   St. Petersburg, FL
   

   USA

   (727) 502-8000 (voice)

   aforde@usgs.gov

   Contact_Instructions:

   The SEG Y files included in this data release are also downloadable from the Coastal and Marine Geoscience Data System https://cmgds.marine.usgs.gov.

2. What's the catalog number I need to order this data set?
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?
   • Availability in digital form:

     Data format:	SEG Y (version Revision 0) Size: 7930
     Network links:	https://coastal.er.usgs.gov/data-release/doi-P9S75Q0U/data/2019-332-FA_segy.zip

     Data format:	ASCII Size: 6.5
     Network links:	https://coastal.er.usgs.gov/data-release/doi-P9S75Q0U/data/2019-332-FA_nav.zip

     Data format:	Shapefile, KMZ Size: 62.3
     Network links:	https://coastal.er.usgs.gov/data-release/doi-P9S75Q0U/data/2019-332-FA_gis.zip

     Data format:	GIF Size: 57.3
     Network links:	https://coastal.er.usgs.gov/data-release/doi-P9S75Q0U/data/2019-332-FA_seisimag.zip

   • Cost to order the data: None

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: 10-Nov-2020

Metadata author:

Arnell S. Forde

U.S. Geological Survey

Geologist

600 4th Street South

St. Petersburg, FL

USA

(727) 502-8000 (voice)

aforde@usgs.gov

Metadata standard:

Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)