Ground Penetrating Radar (GPR) Trackline Locations Collected from Dauphin Island, Alabama in April 2013

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Frequently anticipated questions:


What does this data set describe?

Title:
Ground Penetrating Radar (GPR) Trackline Locations Collected from Dauphin Island, Alabama in April 2013
Abstract:
From April 13-20, 2013, scientists from the U.S. Geological Survey St. Petersburg Coastal and Marine Science Center (USGS-SPCMSC) conducted geophysical surveys and collected sediment samples from Dauphin Island, Alabama. This dataset, Ground Penetrating Radar (GPR) Trackline Locations Collected from Dauphin Island, Alabama, in April 2013, contains geospatial data and raster images of the GPR data. The GPR trackline locations are presented as Geographic Information System (GIS) files and the subsurface profile data are provided as images in Joint Photographic Experts Group (JPEG) format.
Supplemental_Information:
Data were collected during USGS field activity number 13BIM01, additional survey details are available at http://cmgds.marine.usgs.gov/fan_info.php?fan=13BIM01. Funding for this survey was provided by the USGS Coastal and Marine Geology Program’s Barrier Island Evolution Research (BIER) project (http://coastal.er.usgs.gov/bier/). The GIS data for this survey are provided in Environmental Systems Research Institute (Esri) polyline shapefile (.shp) and Keyhole Markup Language (KML) formats; these files can be opened using the free ArcGIS Explorer or Google Earth GIS viewers. The .kml files, profile images, map document, and shapefile used to create the hyperlinked GPR trackline map can be found at pubs.usgs.gov/ds/0982/ds_data_downloads.html. Included in the GIS .zip file is a folder called “images,” which stores the .jpg images of each trackline's subsurface profile. To access these images using ArcMap 10.2, open the map document and then click on the hyperlink button (the symbol is a lightning bolt) located on the toolbar. Once this button is activated, the tracklines will all change to blue, indicating they have hyperlinks. Selecting a trackline will open the associated profile image.
  1. How might this data set be cited?
    Forde, Arnell S., 2016, Ground Penetrating Radar (GPR) Trackline Locations Collected from Dauphin Island, Alabama in April 2013:.

    Online Links:

    This is part of the following larger work.

    Forde, Arnell S., Smith, Christopher G., and Reynolds, Billy J., 2016, Archive of Ground Penetrating Radar Data Collected During USGS Field Activity 13BIM01: Dauphin Island, Alabama, April 2013: U.S. Geological Survey Data Series 982, U.S. Geological Survey, St. Petersburg, FL.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -88.195013
    East_Bounding_Coordinate: -88.074726
    North_Bounding_Coordinate: 30.258131
    South_Bounding_Coordinate: 30.243289
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 15-Apr-2013
    Ending_Date: 17-Apr-2013
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: Vector Digital Data Set (Polyline)
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Vector data set. It contains the following vector data types (SDTS terminology):
      • String (60)
    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 0.0197877137. Longitudes are given to the nearest 0.0227813369. Latitude and longitude values are specified in Decimal seconds. The horizontal datum used is D_WGS_1984.
      The ellipsoid used is WGS_1984.
      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?
    13BIM01_trklns2.shp
    Geospatial data representation showing the locations of all the GPR trickling collected during FAN 13BIM01. (Source: Producer defined)
    Id
    Short form of the sequential line numbers (063-0128) assigned by the GPR acquisition system, during data collection. (Source: USGS)
    Range of values
    Minimum:63
    Maximum:128
    Image
    Joint Photographic Experts Group (JPEG) Image Name (Source: USGS) This field lists the name of the subsurface profile image, in .jpg format, which was created from the post-processed GPR trace data. Each image is associated with the relevant GPR trackline using the hyperlink feature in ArcMap. Some lines were missing post-processed GPS and (or) elevation data so no elevation corrections were applied to these lines; consequently, these lines have "_noelev" appended after the line number.
    Entity_and_Attribute_Overview:
    The entity and attribute information provided here describes the tabular data associated with the dataset. Please review the detailed descriptions that are provided (the individual attribute descriptions) for information on the values that appear as fields/table entries of the dataset.
    Entity_and_Attribute_Detail_Citation:
    The entity and attribute information was 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
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    U.S. Geological Survey, Southeast Region
    Attn: Arnell S Forde
    Geologist
    600 4th Street South
    St. Petersburg, FL

    727-502-8111 (voice)
    727-502-8001 (FAX)
    aforde@usgs.gov

Why was the data set created?

The objectives of this study were to quantify inorganic and organic accretion rates in back-barrier and mainland marsh and estuarine environments. Various field and laboratory methods were used to achieve these objectives, including, subsurface imaging using GPR, sediment sampling, lithologic and microfossil analyses, and geochronology techniques to produce barrier island stratigraphic cross sections to help interpret the recent (last 2000 years) geologic evolution of the island.

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: 01-Aug-2013 (process 1 of 2)
    GPR processing: The GPR data were processed using Sandmeier Scientific Software’s Reflexw Version 7.2.2 geophysical near surface processing and interpretation software (http://www.sandmeier-geo.de/reflexw.html). Each GPR data file was imported into Reflexw, where it was converted from Radan’s DZT (.dzt) format to a .dat file. Processing steps utilized during post processing included applying static correction, subtracting mean (dewow), removing header gain, and applying manual Automatic Gain Control (AGC) gain. After these initial processing steps, the position (either post-processed DGPS or lidar-derived coordinates) and elevation data were integrated into the trace headers. Lastly, all profiles were inspected for data quality to ensure no navigation or trace data gaps were present before being output in American Standard Code for Information Interchange (ASCII) format for the trace data and JPEG format for the profile images. If any issues were discovered during the QA/QC process, this information was noted for each affected line and recorded in this metadata file. A velocity of 0.06 m/ns was used to display depths on the elevation-corrected profiles.
    Date: 22-Apr-2014 (process 2 of 2)
    Navigation processing: During acquisition, uncorrected real-time rover positions were output as a NMEA GGA string at a 9600 baud rate to an external GPS Acumen data logger [puck] and saved as a .plt file. A Matlab script written by Christopher G. Smith was used to extract the line name, time, latitude, and longitude from each GPR line's .plt file and this information was then saved as a comma separated value (CSV) file. Each .csv file was subsequently imported into ArcGIS 10.2 and saved as an individual point shapefile. Once a point shape file had been created for all the GPR lines, the PointsToLine script (located in the ArcToolbox) was used to create individual polyline files for each trackline. The last step involved combining each polyline file into a single shapefile, called 13BIM01_trklns2.shp, using the Arc Toolbox Append tool. In order to use ArcMap’s hyperlink feature to display each line's associated profile image, a field called "Image" was added to the final shapefile’s attribute table. Please note that the “images” folder and map document, included in pubs.usgs.gov/ds/0982/downloads/13BIM01_gis_data.zip, must both be located in the same directory or the hyperlink function will not work.
  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?
    No formal attribute accuracy tests were conducted.
  2. How accurate are the geographic locations?
    Location information associated with each GPR line was determined by post-processed differential correction using a base/rover setup. The field setup consisted of two (rover and base station) Ashtech ProFlex Global Navigation Satellite System (GNSS) receivers and antennas. The GNSS base and rover receivers recorded the raw full-carrier-phase positioning signals (L1/L2) from satellites, via Ashtech GNSS antenna, concurrently at 0.2 seconds (s) (5 Hertz [Hz]) intervals throughout the survey. The base station receiver was positioned on the National Geodetic Survey (NGS) published reference point NGS PID# BH1755 (Station ID: 8735180), located on the east side of the island, at the entrance to Fort Gaines. The vertical offset between the GNSS antenna and the NGS benchmark was 2.476 m. The rover GPS was mounted on a fixed frame above the GPR unit. The offset between the rover GNSS antenna (located on the GPR unit) and the ground was 1.915 meters (m). Raw, uncorrected position data were output from the rover GPS to the GPR as a National Marine Electronics Association (NMEA) GGA string.
  3. How accurate are the heights or depths?
    During acquisition of lines 66-116, the signal between the GPS rover unit and multiple satellites was interrupted or lost, most likely due to dense tree canopy within the survey area. This lack of communication with the satellites caused either incorrect values, missing, or incomplete GPS data to be collected and recorded. For lines missing post-processed GPS and (or) elevation data, elevation and location data were extracted from a topographic lidar survey, which was contracted by the USGS in July 2013 (Guy and Plant, 2013), and this data used instead. In cases where the DGPS data were incomplete or corrupted and lidar data were unavailable, non-elevation corrected profiles have been provided. Lines 65, 120, 121 and 122 were all processed using lidar-extracted location and elevation information. Lines 66-70, 74-82, 88, 92-94, 98, 100, 102, 109-116 and 124 have non-elevation corrected profile images associated with each line.
  4. Where are the gaps in the data? What is missing?
    A total of 65 GPR lines, representing a linear distance of approximately 40 kilometers (km), were acquired during field activity 13BIM01. Due to acquisition errors encountered during the collection of lines 87 (missing GPS information) and 101 (incomplete data file), those files were not processed. No data were collected for lines 112, 113 and 114.
  5. How consistent are the relationships among the observations, including topology?
    No formal logical accuracy tests were conducted.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: None. Please see “Distribution Information” for details.
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 originators of the data in future products or derivative research. 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)
    U.S. Geological Survey, Southeast Region
    Attn: Arnell S Forde
    Geologist
    600 4th Street South
    St. Petersburg, FL

    727-502-8111 (voice)
    727-502-8001 (FAX)
    aforde@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: This zip archive includes the geographic trackline locations in .shp and .kml formats for GPR data collected from Dauphin Island, Alabama in 2013. in format Compressed (zip) archive Vector digital data, tabular digital data, raster data Size: 10.3
      Network links: https://pubs.usgs.gov/ds/0982/downloads/13BIM01_gis_data.zip
    • Cost to order the data: None. No fees are applicable for obtaining the dataset.


Who wrote the metadata?

Dates:
Last modified: 18-Mar-2019
Metadata author:
Arnell S Forde
U.S. Geological Survey, Southeast Region
Geologist
600 4th Street South
St. Petersburg, FL

727-502-8111 (voice)
727-502-8001 (FAX)
aforde@usgs.gov
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

This page is <https://cmgds.marine.usgs.gov/catalog/spcmsc/13BIM01_gis_metadata.faq.html>
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