Ground Penetrating Radar (GPR) Navigation Data 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) Navigation Data 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 and sediment sampling surveys on Dauphin Island, Alabama as part of field activity number 13BIM01. This dataset, Ground Penetrating Radar (GPR) Navigation Data Collected from Dauphin Island, Alabama, in April 2013, contains the processed, differentially corrected position data obtained during this survey.
Supplemental_Information:
Data were collected during USGS field activity 13BIM0. 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 post-processed Global Positioning System (GPS) data for this survey are provided in American Standard Code for Information Interchange (ASCII) format.
  1. How might this data set be cited?
    Forde, Arnell S., 2016, Ground Penetrating Radar (GPR) Navigation Data 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: 13-Apr-2013
    Ending_Date: 20-Apr-2013
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: Tabular Digital Data
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
    2. What coordinate system is used to represent geographic features?
  7. How does the data set describe geographic features?
    Entity_and_Attribute_Overview:
    The entity and attribute information provided here describes the tabular data associated with 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 Ground Penetrating Radar (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: 13-Apr-2013 (process 1 of 2)
    Navigation Acquisition: 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 m. Uncorrected positions were output from the rover GPS to the GPR as a National Marine Electronics Association (NMEA) GGA string at a 9600 baud rate.
    Date: 22-Apr-2014 (process 2 of 2)
    Navigation processing: The coordinate values for the GNSS base station were checked using the time-weighted average of values obtained from the NGS On-Line Positioning User Service (OPUS). The average of the coordinates from all the occupations collected at the base during the survey did not differ significantly from the NGS published coordinates; therefore, the published coordinates were used for post-processing. The kinematic GNSS data from the GPR were post-processed using the concurrent GNSS data from the base station. The raw base station and rover data were imported into NovAtel GrafNav version 8.4 software and were post-processed by differential correction. During processing, steps were taken to ensure that the trajectories between the base and rover were clean, resulting in fixed positions. By analyzing the graphs, trajectory maps, and processing logs that GrafNav produces for each GNSS session, data from satellites flagged by the program as having poor health or satellite time segments that had cycle slips could be excluded, or the satellite elevation mask angle could be adjusted to improve the position solutions. The final, differentially corrected, precise DGPS positions were computed at 1-s intervals for each roving GNSS session and exported in American Standard Code for Information Interchange (ASCII) text format (as a GGA string), which replaced the uncorrected real-time rover positions recorded during acquisition. The GPS data were acquired, processed, and exported in the World Geodetic System of 1984 (WGS84) (G1150) geodetic datum. 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 to be recorded or missing/incomplete GPS data to be collected. For lines missing post-processed GPS and (or) elevation data, elevation and location data were extracted from a topographic light detection and ranging (lidar) survey, which was contracted by the USGS in July 2013 and 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 with post-processed GPS and elevation data issues are noted in this metadata file.
  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 m. Uncorrected positions were output from the rover GPS to the GPR as a National Marine Electronics Association (NMEA) GGA string at a 9600 baud rate.
  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 to be recorded or missing/incomplete GPS data to be collected. 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 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 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 Info” 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?

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_gps_metadata.faq.html>
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