Metadata: Identification_Information: Citation: Citation_Information: Originator: Ferdinand K. Oberle Originator: Cordell Johnson Originator: Joshua Logan Originator: Curt D. Storlazzi Publication_Date: 2025 Title: Nearshore Electrical Resistivity Tomography (ERT) profile data, Ofu, American Samoa, February 2020 Geospatial_Data_Presentation_Form: comma-delimited text Series_Information: Series_Name: data release Issue_Identification: doi:10.5066/P1QPSVMZ Publication_Information: Publication_Place: Pacific Coastal and Marine Science Center, Santa Cruz, California Publisher: U.S. Geological Survey 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. Online_Linkage: https://doi.org/10.5066/P1QPSVMZ Online_Linkage: https://www.sciencebase.gov/catalog/item/67cb2b30d34ed37377098966 Description: Abstract: Along-shore surface-based 2D electrical resistivity tomography (ERT) surveys were collected in the nearshore region of Ofu, American Samoa. Purpose: 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. 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. Time_Period_of_Content: Time_Period_Information: Range_of_Dates/Times: Beginning_Date: 20200130 Ending_Date: 20200205 Currentness_Reference: ground condition at time data were collected Status: Progress: Complete Maintenance_and_Update_Frequency: None planned Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -169.666836 East_Bounding_Coordinate: -169.657184 North_Bounding_Coordinate: -14.180402 South_Bounding_Coordinate: -14.184693 Keywords: Theme: Theme_Keyword_Thesaurus: ISO 19115 Topic Category Theme_Keyword: biota Theme_Keyword: geoscientificInformation Theme: Theme_Keyword_Thesaurus: Global Change Master Directory (GCMD) Theme_Keyword: THERMOCLINE Theme_Keyword: CORAL REEFS Theme: Theme_Keyword_Thesaurus: Data Categories for Marine Planning Theme_Keyword: Water Column Features Theme: Theme_Keyword_Thesaurus: USGS Thesaurus Theme_Keyword: time series datasets Theme_Keyword: electrical resistivity tomography Theme_Keyword: ERT surveying Theme_Keyword: resistivity Theme: Theme_Keyword_Thesaurus: Marine Realms Information Bank (MRIB) keywords Theme_Keyword: physical oceanography Theme: Theme_Keyword_Thesaurus: None Theme_Keyword: U.S. Geological Survey Theme_Keyword: USGS Theme_Keyword: Coastal and Marine Hazards and Resources Program Theme_Keyword: CMHRP Theme_Keyword: Pacific Coastal and Marine Science Center Theme_Keyword: PCMSC Theme: Theme_Keyword_Thesaurus: USGS Metadata Identifier Theme_Keyword: USGS:67cb2b30d34ed37377098966 Place: Place_Keyword_Thesaurus: Geographic Names Information System (GNIS) Place_Keyword: Ofu Place_Keyword: Papaloloa Point Place_Keyword: Fatuana Point Place_Keyword: South Pacific Ocean Place_Keyword: Territory of American Samoa Place: Place_Keyword_Thesaurus: None Place_Keyword: National Park of American Samoa Place_Keyword: American Samoa Place_Keyword: Polynesia region 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. Point_of_Contact: Contact_Information: Contact_Organization_Primary: Contact_Organization: U.S. Geological Survey, Pacific Coastal and Marine Science Center Contact_Person: PCMSC Science Data Coordinator Contact_Address: Address_Type: mailing and physical Address: 2885 Mission Street City: Santa Cruz State_or_Province: CA Postal_Code: 95060 Contact_Voice_Telephone: 831-460-4747 Contact_Electronic_Mail_Address: pcmsc_data@usgs.gov Native_Data_Set_Environment: Raw data from the resistivity array were processed using the manufacturers software, AGI Earth Imager, on a Dell Personal Computer running Windows 11 Operating System. Data_Quality_Information: Attribute_Accuracy: Attribute_Accuracy_Report: No formal attribute accuracy tests were conducted. Logical_Consistency_Report: Data fall within expected ranges. Completeness_Report: 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. Positional_Accuracy: Horizontal_Positional_Accuracy: Horizontal_Positional_Accuracy_Report: 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. Lineage: Process_Step: Process_Description: 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. Process_Date: 20240804 Process_Step: Process_Description: Resistivity data were processed using the manufacture’s software, AGI Earth Imager, and data exported to comma-delimited text files. Process_Date: 20241021 Spatial_Data_Organization_Information: Direct_Spatial_Reference_Method: Point Spatial_Reference_Information: Horizontal_Coordinate_System_Definition: Geographic: Latitude_Resolution: 0.00000001 Longitude_Resolution: 0.0000001 Geographic_Coordinate_Units: Decimal degrees Geodetic_Model: Horizontal_Datum_Name: D_WGS_1984 Ellipsoid_Name: WGS_1984 Semi-major_Axis: 6378137.0 Denominator_of_Flattening_Ratio: 298.257223563 Entity_and_Attribute_Information: Detailed_Description: Entity_Type: Entity_Type_Label: Table Entity_Type_Definition: Comma-delimited table of a vertical profile of the resistivity of soil to electrical conductance. The first row contains column headers. Entity_Type_Definition_Source: Producer defined Attribute: Attribute_Label: Distance_Along_Transect_(m) Attribute_Definition: Along-transect distance of vertical resistivity profiles measured from the beginning lat/lon. Attribute_Definition_Source: Electrode spacing Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: 0.0 Range_Domain_Maximum: 110.0 Attribute_Units_of_Measure: meters Attribute_Measurement_Resolution: 0.1 Attribute: Attribute_Label: Depth_from_surface_(m) Attribute_Definition: Depth below ground of resistivity measurement at each probe Attribute_Definition_Source: Producer defined Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: -22.81 Range_Domain_Maximum: 4.0 Attribute_Units_of_Measure: meters Attribute_Measurement_Resolution: 0.1 Attribute: Attribute_Label: Resistivity_(ohm m) Attribute_Definition: Resistivity of soil to electrical conductance Attribute_Definition_Source: Producer defined Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: 0.58 Range_Domain_Maximum: 4127.03 Attribute_Units_of_Measure: Ohm meters Attribute_Measurement_Resolution: 0.01 Attribute: Attribute_Label: Latitude_(WGS) Attribute_Definition: 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. Attribute_Definition_Source: Global Positioning System Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: -14.18469331 Range_Domain_Maximum: -14.18091509 Attribute_Units_of_Measure: decimal degrees Attribute_Measurement_Resolution: 0.00000001 Attribute: Attribute_Label: Longitude_(WGS) Attribute_Definition: 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. Attribute_Definition_Source: Global Positioning System Attribute_Domain_Values: Range_Domain: Range_Domain_Minimum: -169.6668360 Range_Domain_Maximum: -169.6580912 Attribute_Units_of_Measure: decimal degrees Attribute_Measurement_Resolution: 0.0000001 Overview_Description: 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 Distribution_Information: Distributor: Contact_Information: Contact_Organization_Primary: Contact_Organization: U.S. Geological Survey - ScienceBase Contact_Address: Address_Type: mailing and physical Address: Denver Federal Center, Building 810, Mail Stop 302 City: Denver State_or_Province: CO Postal_Code: 80225 Contact_Voice_Telephone: 1-888-275-8747 Contact_Electronic_Mail_Address: sciencebase@usgs.gov Resource_Description: 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. Distribution_Liability: 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. Standard_Order_Process: Digital_Form: Digital_Transfer_Information: Format_Name: comma-delimited text Format_Version_Date: 20180818 Format_Information_Content: Zip file contains the csv tables. File_Decompression_Technique: Windows users can use WinZIP to uncompress the files; Apple Macintosh users, Archive Utility; Linux and Unix users, gunzip. Transfer_Size: .03872 Digital_Transfer_Option: Online_Option: Computer_Contact_Information: Network_Address: Network_Resource_Name: https://www.sciencebase.gov/catalog/file/get/67cb2b30d34ed37377098966 Network_Resource_Name: https://doi.org/10.5066/P1QPSVMZ Access_Instructions: Data can be downloaded using the Network_Resource_Name links. The first link is a direct link to download a zipped file of data and metadata. The second link points to a landing page with metadata and data for the entire data release. Fees: None. Technical_Prerequisites: These data can be viewed with any text editor software. Metadata_Reference_Information: Metadata_Date: 20250429 Metadata_Contact: Contact_Information: Contact_Organization_Primary: Contact_Organization: U.S. Geological Survey, Pacific Coastal and Marine Science Center Contact_Person: PCMSC Science Data Coordinator Contact_Address: Address_Type: mailing and physical Address: 2885 Mission Street City: Santa Cruz State_or_Province: CA Postal_Code: 95060 Contact_Voice_Telephone: 831-460-4747 Contact_Electronic_Mail_Address: pcmsc_data@usgs.gov Metadata_Standard_Name: Content Standard for Digital Geospatial Metadata Metadata_Standard_Version: FGDC-STD-001-1998