Ground Penetrating Radar (GPR) Profile Trace Data Collected from Dauphin Island, Alabama in April 2013
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) Profile Trace Data Collected from Dauphin Island, Alabama in April 2013, contains the unprocessed, raw profile trace data obtained during this survey.
Data were collected during USGS field activity 13BIM01. Additional survey details are available at https://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 (https://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.
Forde, Arnell S., Smith, Christopher G., and Reynolds, Billy J., 20160318, 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.
The entity and attribute information provided here describes the tabular data associated with the dataset. The trace data files, included in 13BIM01_gpr_trace_data.zip, were exported from Reflex using the "ASCII-4COLUMS" option, which contains the x-coordinate, y-coordinate, time, and amplitude (saved in ASCII format) for each GPR line collected during the survey.
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.
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.
GPR Acquisition: A total of 65 GPR lines, representing a linear distance of approximately 40.23 km, were acquired during field activity 13BIM01. Data were collected, over various terrains, either on foot or towed at slow speeds (>10 mph) behind a vehicle. The GPR data were collected with a Geophysical Survey Systems, Inc. (GSSI) TerraSIRch SIR System-3000. This system collects single channel GPR and contains a Digital Control Unit (model DC-3000), 10.8 V Lithium-Ion rechargeable battery (which allows up to 3 hours of survey time), a 200 MHz antenna and cables, and a 16-inch survey wheel (model 620) that acquired 417 ticks/meter. Additional equipment used in conjunction with the GSSI included: an external [puck] GPS Acumen data logger, support poles and hardware (for the GPS system), and harness and tow strap. The GPR system's internal memory capacity is roughly 1 GB of data; however, to ensure there would be no data loss, files were recorded to both the internal memory and a SanDisk CompactFlash (CF) memory card. Acquisition settings for the subsurface profiles were set to 64 scans/s, 20 scans/unit (m), 1024 samples/sec 16 bits/sample, dielectric constant = 15, range = 200 ns, and auto gain. Due to the homogeneous nature of Dauphin Island's near surface deposits, the preceding settings were applicable for most lines; however, adjustments were made when changes to the terrain or subsurface geology warranted such modifications. An Infinite Impulse Response (IIR) filter was used (Lowpass = 600 MHz and Highpass = 50 MHz) to downplay external interference, thus cleaning up the signal. Each day, prior to collecting any data, the distance setting was used to manually calibrate the survey wheel for the terrain by laying out a 10 m long measured line on the survey surface, which varied between sandy dune slopes, asphalt and grass. Calibration steps consisted of (1) entering the calibration distance, (2) positioning the antenna at the start of the calibration line, ensuring that the same part of the antenna positioned at line start also ended at the terminus of survey line and, (3) lastly pulling the wheel the pre-determined distance. These steps were repeated until a satisfactory average value was obtained, at which time it was saved into the system. Data was acquired using RADAN 7 proprietary software [in TerraSIRch mode] and saved in .dzt format.
Date: 22-Apr-2014 (process 2 of 4)
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 Reflex, where it was converted from Radan's DZT (.dzt) format to a .dat file. Next, a variety of processing steps were used including applying static correction, subtracting mean (dewow), removing header gain, and applying manual AGC gain. After these initial processing steps, the GPS (either post-processed DGPS or Lidar-derived GPS) 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 Joint Photographic Experts Group (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 the metadata included in this report. A velocity of 0.06 m/ns was used to calculate and display depth on the elevation-corrected profiles. Lines with post-processed GPS and elevation data issues are noted in this metadata file.
Date: 26-Mar-2018 (process 3 of 4)
Keywords section of metadata optimized by adding theme keyword thesauri and associated keywords.
Person who carried out this activity:
U.S. Geological Survey
Attn: Arnell S. Forde
600 4th Street South
St. Petersburg, FL
Date: 13-Oct-2020 (process 4 of 4)
Added keywords section with USGS persistent identifier as theme keyword.
Person who carried out this activity:
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.
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.
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.
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.
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.