Nearshore Electrical Resistivity Tomography (ERT) profile data, Ofu, American Samoa, February 2020

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Frequently anticipated questions:

What does this data set describe?

Title:
Nearshore Electrical Resistivity Tomography (ERT) profile data, Ofu, American Samoa, February 2020
Abstract:
Along-shore surface-based 2D electrical resistivity tomography (ERT) surveys were collected in the nearshore region of Ofu, American Samoa.
Supplemental_Information:
Additional information about the field activity from which these data were derived is available online at: https://cmgds.marine.usgs.gov/fan_info.php?fan=2020-620-FA Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
  1. How might this data set be cited?
    Oberle, Ferdinand K., Johnson, Cordell, Logan, Joshua, and Storlazzi, Curt D., 2025, Nearshore Electrical Resistivity Tomography (ERT) profile data, Ofu, American Samoa, February 2020: data release doi:10.5066/P1QPSVMZ, U.S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, California.

    Online Links:

    Other_Citation_Details:
    Suggested Citation: Oberle, F.K., Johnson, C., Logan, J.B., Storlazzi, C.D., 2025, USGS Nearshore Electrical Resistivity Tomography (ERT) profile data, Ofu, American Samoa: U.S. Geological Survey data release, https://doi.org/10.5066/P1QPSVMZ.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -169.666836
    East_Bounding_Coordinate: -169.657184
    North_Bounding_Coordinate: -14.180402
    South_Bounding_Coordinate: -14.184693
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 30-Jan-2020
    Ending_Date: 05-Feb-2020
    Currentness_Reference:
    ground condition at time data were collected
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: comma-delimited text
  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 0.00000001. Longitudes are given to the nearest 0.0000001. Latitude and longitude values are specified in Decimal degrees. 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?
    Table
    Comma-delimited table of a vertical profile of the resistivity of soil to electrical conductance. The first row contains column headers. (Source: Producer defined)
    Distance_Along_Transect_(m)
    Along-transect distance of vertical resistivity profiles measured from the beginning lat/lon. (Source: Electrode spacing)
    Range of values
    Minimum:0.0
    Maximum:110.0
    Units:meters
    Resolution:0.1
    Depth_from_surface_(m)
    Depth below ground of resistivity measurement at each probe (Source: Producer defined)
    Range of values
    Minimum:-22.81
    Maximum:4.0
    Units:meters
    Resolution:0.1
    Resistivity_(ohm m)
    Resistivity of soil to electrical conductance (Source: Producer defined)
    Range of values
    Minimum:0.58
    Maximum:4127.03
    Units:Ohm meters
    Resolution:0.01
    Latitude_(WGS)
    Latitude in decimal degrees of the beginning and ending of the survey transect line. Empty cells indicate the middle of the survey transect line where no positional data were collected. (Source: Global Positioning System)
    Range of values
    Minimum:-14.18469331
    Maximum:-14.18091509
    Units:decimal degrees
    Resolution:0.00000001
    Longitude_(WGS)
    Longitude in decimal degrees of the beginning and ending of the survey transect line. Empty cells indicate the middle of the survey transect line where no positional data were collected. (Source: Global Positioning System)
    Range of values
    Minimum:-169.6668360
    Maximum:-169.6580912
    Units:decimal degrees
    Resolution:0.0000001
    Entity_and_Attribute_Overview:
    The first line of the csv file is a header line. Latitude and longitude were only measured at the beginning and ending of the ERT transect, and as such, horizontal coordinates are not available at each transect point. However, the transect is a straight line, and the distance of each point along the transect was measured by tape measure.
    Entity_and_Attribute_Detail_Citation: U.S. Geological Survey

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Ferdinand K. Oberle
    • Cordell Johnson
    • Joshua Logan
    • Curt D. Storlazzi
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    U.S. Geological Survey, Pacific Coastal and Marine Science Center
    Attn: PCMSC Science Data Coordinator
    2885 Mission Street
    Santa Cruz, CA

    831-460-4747 (voice)
    pcmsc_data@usgs.gov

Why was the data set created?

Profiles of resistivity on the shoreline will be used to assess the potential for terrestrial groundwater intrusion on the reef and the sources and fate of these water masses.

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: 04-Aug-2024 (process 1 of 2)
    Surface-based 2D Electrical Resistivity Tomography (ERT) surveys were conducted alongshore at the shoreline for one week in late January and early February of 2020 using a SuperSting R8 (AGI, Austin, Texas, USA) and cable with 56 electrodes at 2-m spacing. A dipole-dipole (DD) array was used with a max n-spacing of 7.
    Date: 21-Oct-2024 (process 2 of 2)
    Resistivity data were processed using the manufacture’s software, AGI Earth Imager, and data exported to comma-delimited text files.
  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?
    A formal accuracy assessment of the horizontal positional information in the data set has not been conducted. Latitude and longitude were only measured at the beginning and ending of the ERT transect, and as such, horizontal coordinates are not available at each transect point. However, the transect is a straight line, and the distance of each point along the transect was measured by tape measure. The stated accuracy of the GPS unit used to determine the beginning and ending of the ERT transect is +/- 5m.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    Dataset is considered complete for the information presented, as described in the abstract. Users are advised to read the metadata for each part of this data release carefully for additional details.
  5. How consistent are the relationships among the observations, including topology?
    Data fall within expected ranges.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints No restrictions or legal prerequisites for accessing the dataset.
Use_Constraints USGS-authored or produced data and information are in the public domain from the U.S. Government and are freely redistributable with proper metadata and source attribution. Please recognize and acknowledge the U.S. Geological Survey as the originator(s) of the dataset and in products derived from these data.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey - ScienceBase
    Denver Federal Center, Building 810, Mail Stop 302
    Denver, CO

    1-888-275-8747 (voice)
    sciencebase@usgs.gov
  2. What's the catalog number I need to order this data set? Two transect lines of resistivity data are available in comma-delimited csv format contained in a single zip file (Ofu20_ERT_Data.zip) accompanied by CSDGM FGDC-compliant metadata.
  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 on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty.
  4. How can I download or order the data?
  5. What hardware or software do I need in order to use the data set?
    These data can be viewed with any text editor software.

Who wrote the metadata?

Dates:
Last modified: 29-Apr-2025
Metadata author:
U.S. Geological Survey, Pacific Coastal and Marine Science Center
Attn: PCMSC Science Data Coordinator
2885 Mission Street
Santa Cruz, CA

831-460-4747 (voice)
pcmsc_data@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/pcmsc/DataReleases/ScienceBase/DR_P1QPSVMZ/Ofu20_ERT_metadata.faq.html>
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