Eagle airborne magnetic and radiometric geophysical survey

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Frequently anticipated questions:


What does this data set describe?

Title: Eagle airborne magnetic and radiometric geophysical survey
Abstract:
Eagle airborne magnetic and radiometric geophysical survey, Geophysical Report 2021-2 v. 2, covers parts of the Nulato Quadrangle west of Fairbanks, Alaska. Magnetic and radiometric data were collected with a helicopter between June 4 and 17, 2024, by EON Geosciences Inc. The survey contains a single block covering 1,975 km², which includes an infill block with tighter line spacing located in the northcentral portion of the block. A total of 6,459 line-kilometers were collected. The magnetometer was installed inside the stinger attached to the helicopter nose, and the airborne gamma-ray spectrometer was mounted on the interior floor of the helicopter cabin. The block was flown with a line spacing of 400 m, and the northcentral infill block was flown with 200 m spacing. Tie-lines for magnetic leveling were flown at 1,600 m spacing. We updated this dataset in 2025 to refine processing, removing artifacts and excess noise present in the final products provided by the original contractor. The raw data were reprocessed by Baigent Geosciences. The International Geomagnetic Reference Field correction was recalculated accounting for aircraft height, and the data were relevelled using Baigent Geosciences software. A complete and detailed report on the reprocessing steps undertaken is included in the publication documents. The result of the reprocessing is that leveling artifacts have been removed and the data now display finer features, including well-defined lineaments and other anomalies which were not present in the original contractor grids. The data, as well as additional metadata, are available from the DGGS website: http://doi.org/10.14509/31694.
Supplemental_Information:
ascii_data:    ASCII format line data, other ASCII data	
databases_geosoft:    Geosoft format database of final line data, other Geosoft format databases	
documents:    Project report, calibration reports	
grids_geosoft:    Oasis montaj Geosoft GRD format gridded data	
grids_tif:    Geographically registered data value rasters of gridded data, GeoTiff format	
maps_pdf_format:    Printable and geographically registered maps in pdf format. Compatible with mobile device navigation and desktop mapping applications.	
video_flightpath:    Survey flight path downward facing video	
vector_data:    Line path and survey boundary in Esri shapefile (shp) format
  1. How might this data set be cited?
    Emond, A.M., LTD, MPX Geophysics, Baigent, Mark, Fusso, L.A., and Petersen, E.I., 2025, Eagle airborne magnetic and radiometric geophysical survey: Geophysical Report GPR 2021-2 v. 2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 4 p.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -143.582148
    East_Bounding_Coordinate: -140.944196
    North_Bounding_Coordinate: 65.221429
    South_Bounding_Coordinate: 63.978089
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 2021
    Ending_Date: 2024
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: digital, data
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a raster data set.
    2. What coordinate system is used to represent geographic features?
      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 7
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -141
      Latitude_of_Projection_Origin: 0
      False_Easting: 500000.000000
      False_Northing: 0
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest .00000001
      Ordinates (y-coordinates) are specified to the nearest .00000001
      Planar coordinates are specified in Meters
      The horizontal datum used is WGS84.
      The ellipsoid used is WGS 84.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257223563.
  7. How does the data set describe geographic features?
    ascii_data
    ASCII format line data, other ASCII data (Source: MPX Geophysics LTD)
    databases_geosoft
    Geosoft format database of final line data, other Geosoft format databases (Source: MPX Geophysics LTD)
    documents
    Project report, calibration reports (Source: MPX Geophysics LTD and Alaska Division of Geological & Geophysical Surveys (DGGS))
    grids_geosoft
    Oasis montaj Geosoft GRD format gridded data (Source: MPX Geophysics LTD and Alaska Division of Geological & Geophysical Surveys (DGGS))
    grids_tif
    Geographically registered data value rasters of gridded data, GeoTiff format (Source: Alaska Division of Geological & Geophysical Surveys (DGGS))
    maps_pdf_format
    Printable and geographically registered maps in pdf format. Compatible with mobile device navigation and desktop mapping applications. (Source: MPX Geophysics LTD)
    video_flightpath
    Survey flight path downward facing video (Source: MPX Geophysics LTD)
    vector_data
    Line path and survey boundary in Esri shapefile (shp) format (Source: Alaska Division of Geological & Geophysical Surveys (DGGS))

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
  2. Who also contributed to the data set?
    This work was supported by the Bureau of Land Management grant L18AC00019 and the U.S. Geological Survey's Earth MRI program grant G20AC00160. Reprocessing efforts were supported by the State of Alaska, capital improvement project funds. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government.
  3. To whom should users address questions about the data?
    Alaska Division of Geological & Geophysical Surveys
    Metadata Manager
    3354 College Road
    Fairbanks, AK
    USA

    (907)451-5020 (voice)
    (907)451-5050 (FAX)
    dggspubs@alaska.gov
    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
    Contact_Instructions:
    Please view our website (https://www.dggs.alaska.gov) for the latest information on available data. Please contact us using the e-mail address provided above when possible.

Why was the data set created?

The data from the Eagle airborne magnetic and radiometric geophysical survey will improve the understanding of the geology and mineral potential of the area, promote resource exploration, and be a part of the continuous regional magnetic data coverage of the Yukon Tanana Uplands.

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: 2021 (process 1 of 3)
    Data acquisition - The Eagle airborne magnetic and radiometric geophysical survey covers parts of the Charley River, Eagle, and Tanacross quadrangles near Eagle, Alaska. Magnetic and radiometric data were collected with a fixed-wing aircraft May 24 to June 27, 2021 by MPX Geophysics LTD. A total of 26,926 line kilometers were collected covering 9,731 square kilometers. The magnetometer was mounted to a rear-facing fixed boom ('tail stinger'), and the radiometric crystals were located in the cabin of the aircraft. The Eagle survey was flown with a line spacing of 400 meters and a mean ground clearance of 330 meters.
    Date: 2025 (process 2 of 3)
    Data refinement and reprocessing - In 2025, the dataset was updated to refine processing and remove artifacts and excess noise present in the final products provided by the original contractor. The raw data were reprocessed by Baigent Geosciences. The International Geomagnetic Reference Field correction was recalculated accounting for aircraft height, and the data were relevelled using Baigent Geosciences software. A complete and detailed report on the reprocessing steps undertaken is included in the publication documents. The result of the reprocessing is that leveling artifacts have been removed and the data now display finer features, including well-defined lineaments and other anomalies which were not present in the original contractor grids.
    Date: 2025 (process 3 of 3)
    Data cataloged for archival and publication - Final data were published and archived by DGGS.
  3. What similar or related data should the user be aware of?
    Emond, A.M., and LTD, MPX Geophysics, 2022, Tanana River and Big Delta airborne magnetic and radiometric survey: Geophysical Report GPR 2022-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 4 p
    Emond, A.M., Minsley, B.J., Daanen, R.P., Graham, G.R.C., and CGG, 2018, Airborne electromagnetic and magnetic survey, western Yukon Flats, interior Alaska: Geophysical Report GPR 2016-2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 3 p
    Burns, L.E., Geoterrex-Dighem, Stevens Exploration Management Corp., Emond, A.M., and Graham, G.R.C., 2015, Fortymile mining district electromagnetic and magnetic airborne geophysical survey data compilation: Geophysical Report GPR 2015-4, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 12 p

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
    Geophysical data were acquired according to the contractor, contract, and request-for-proposals specifications. For additional detail about survey parameters, see the accompanying project report available in the documents directory of this data distribution package.
  2. How accurate are the geographic locations?
    Station coordinates were positioned using a real-time or post-processed corrected differential GPS.
  3. How accurate are the heights or depths?
    Not applicable
  4. Where are the gaps in the data? What is missing?
    This data set includes files that contain processed aeromagnetic measurements, radiometric measurements, magnetic measurements, altimetry measurements, and locational data for the entire survey area.
  5. How consistent are the relationships among the observations, including topology?
    Data originate from one company using DGGS contract specifications for all data (see accompanying project report). The originating coordinate system was retained for all publication products.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints:
This report, map, and/or dataset is available directly from the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (see contact information below).
Use_Constraints:
Any hard copies or published datasets utilizing these datasets shall clearly indicate their source. If the user has modified the data in any way, the user is obligated to describe the types of modifications the user has made. The user specifically agrees not to misrepresent these datasets, nor to imply that changes made by the user were approved by the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys. The State of Alaska makes no express or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.
  1. Who distributes the data set? (Distributor 1 of 1)
    Alaska Division of Geological & Geophysical Surveys
    Metadata Manager
    3354 College Road
    Fairbanks, AK
    USA

    (907)451-5020 (voice)
    (907)451-5050 (FAX)
    dggspubs@alaska.gov
    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
    Contact_Instructions:
    Please view our website (https://www.dggs.alaska.gov) for the latest information on available data. Please contact us using the e-mail address provided above when possible.
  2. What's the catalog number I need to order this data set? GPR 2021-2 v. 2
  3. What legal disclaimers am I supposed to read?
    The State of Alaska makes no expressed or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 26-Sep-2025
Metadata author:
Alaska Division of Geological & Geophysical Surveys
Attn: Simone Montayne
Metadata Manager
3354 College Road
Fairbanks, AK
USA

(907)451-5020 (voice)
(907)451-5050 (FAX)
dggspubs@alaska.gov
Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:

Generated by mp version 2.9.50 on Mon Sep 29 11:58:44 2025