Nyac magnetic airborne geophysical survey data compilation

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Frequently anticipated questions:


What does this data set describe?

Title: Nyac magnetic airborne geophysical survey data compilation
Abstract:
This geophysical survey is located in southwestern Alaska in the Nyac mining district near Bethel, about 520 kilometers west of Anchorage, Alaska. The data for this magnetic-only survey were collected from August to September 1993. A total of 1366 line kilometers were collected covering 502 square kilometers. Line spacing was 400 meters (m). Data were collected 30 m above the ground surface from a helicopter towed sensor platform ("bird") on a 30 m long line. The data, as well as additional metadata, are available from the DGGS website: <http://doi.org/10.14509/30169>.
Supplemental_Information:
ascii_data:    ASCII format line data, other ASCII data	
databases_geosoft:    Geosoft format database of line data, other Geosoft format databases	
documents:    Project and field reports, survey background information, gridded data explanations, other supporting documentation	
grids_ermapper:    Geographically registered gridded data, ER Mapper ERS format	
grids_geosoft:    Geosoft-format binary grids, these grids can be viewed in ESRI ArcMap using a free plugin from Geosoft	
images_registered:    GeoTiff format images of all gridded data	
kmz:    Keyhole markup language (kml) kmz archive files of project data. Viewable in Google Earth and other compatible programs	
maps_pdf_format:    Printable maps in pdf format	
maps_prn_format:    Printable maps in HPGL/2 printer file format with extension .prn	
profiles_stacked:    Distance-based profiles of the digitally recorded geophysical data are generated and plotted at an appropriate scale. The profiles display electromagnetic anomalies with their respective interpretive symbols	
vector_data:    Line path, data contours, and survey boundary in ESRI shapefile (SHP) format, ESRI Geodatabase format, and/or AutoCAD dxf format	
video_flightpath:    Survey flight path downward-facing video
  1. How should this data set be cited?

    Burns, L.E., Barefoot, J.D., Woods, Rebecca-Ellen, WGM Mining and Geological Consultants, Inc., and Dighem Surveys and Processing, 2019, Nyac magnetic airborne geophysical survey data compilation: Geophysical Report GPR 2019-4, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 3 p.

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -160.163260
    East_Bounding_Coordinate: -159.638530
    North_Bounding_Coordinate: 61.131602
    South_Bounding_Coordinate: 60.903286

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Calendar_Date: 1993
    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?

    2. What coordinate system is used to represent geographic features?

      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 4
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -159
      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 North American Datum of 1927.
      The ellipsoid used is Clarke 1866.
      The semi-major axis of the ellipsoid used is 6378206.40000000037.
      The flattening of the ellipsoid used is 1/294.978698199999997.

  7. How does the data set describe geographic features?

    ascii_data
    ASCII format line data, other ASCII data (Source: WGM Mining and Geological Consultants, Inc. and Dighem Surveys and Processing)

    databases_geosoft
    Geosoft format database of line data, other Geosoft format databases (Source: WGM Mining and Geological Consultants, Inc. and Dighem Surveys and Processing)

    documents
    Project and field reports, survey background information, gridded data explanations, other supporting documentation (Source: WGM Mining and Geological Consultants, Inc. and Dighem Surveys and Processing and Alaska Division of Geological & Geophysical Surveys (DGGS))

    grids_ermapper
    Geographically registered gridded data, ER Mapper ERS format (Source: WGM Mining and Geological Consultants, Inc. and Dighem Surveys and Processing and Alaska Division of Geological & Geophysical Surveys (DGGS))

    grids_geosoft
    Geosoft-format binary grids, these grids can be viewed in ESRI ArcMap using a free plugin from Geosoft (Source: WGM Mining and Geological Consultants, Inc. and Dighem Surveys and Processing and Alaska Division of Geological & Geophysical Surveys (DGGS))

    images_registered
    GeoTiff format images of all gridded data (Source: Alaska Division of Geological & Geophysical Surveys (DGGS))

    kmz
    Keyhole markup language (kml) kmz archive files of project data. Viewable in Google Earth and other compatible programs (Source: Alaska Division of Geological & Geophysical Surveys (DGGS))

    maps_pdf_format
    Printable maps in pdf format (Source: WGM Mining and Geological Consultants, Inc. and Dighem Surveys and Processing)

    maps_prn_format
    Printable maps in HPGL/2 printer file format with extension .prn (Source: WGM Mining and Geological Consultants, Inc. and Dighem Surveys and Processing)

    profiles_stacked
    Distance-based profiles of the digitally recorded geophysical data are generated and plotted at an appropriate scale. The profiles display electromagnetic anomalies with their respective interpretive symbols (Source: WGM Mining and Geological Consultants, Inc. and Dighem Surveys and Processing)

    vector_data
    Line path, data contours, and survey boundary in ESRI shapefile (SHP) format, ESRI Geodatabase format, and/or AutoCAD dxf format (Source: WGM Mining and Geological Consultants, Inc. and Dighem Surveys and Processing and Alaska Division of Geological & Geophysical Surveys (DGGS))

    video_flightpath
    Survey flight path downward-facing video (Source: WGM Mining and Geological Consultants, Inc. and Dighem Surveys and Processing)


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?

    Funding was provided by the Alaska State Legislature as part of the DGGS Airborne Geophysical/Geological Mineral Inventory (AGGMI) program.

  3. To whom should users address questions about the data?

    Alaska Division of Geological & Geophysical Surveys
    Metadata Manager
    3354 College Road
    Fairbanks, AK 99709-3707
    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


Why was the data set created?

This airborne geophysical survey is part of a program to acquire data on Alaska's most promising mineral belts and districts. The information acquired is aimed at catalyzing new private sector exploration, discovery, and ultimate development and production. The purpose of the survey was to map the magnetic properties of the survey area, which has been an important producer of placer gold since 1908. Other gold and base-metal anomalies, altered zones, favorable lithologies, and structural zones are known to exist throughout the survey area.


How was the data set created?

  1. From what previous works were the data drawn?

    Alaska Division of Geological & Geophysical Surveys and others, 1994 (source 1 of 9)
    Alaska Division of Geological & Geophysical Surveys, WGM, Inc., and Dighem, 1994, 7200 Hz resistivity contours of Circle mining district: Public Data File PDF 94-12, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:63,360
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 63360
    Source_Contribution: Data collection, processing, and delivery

    Alaska Division of Geological & Geophysical Surveys and others, 1994 (source 2 of 9)
    Alaska Division of Geological & Geophysical Surveys, WGM, Inc., and Dighem, 1994, Clear mylar version of RI 94-3: Total field magnetics of the Nyac mining district: Public Data File PDF 94-18, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:63,360
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 63360
    Source_Contribution: Data collection, processing, and delivery

    Alaska Division of Geological & Geophysical Surveys and others, 1994 (source 3 of 9)
    Alaska Division of Geological & Geophysical Surveys, WGM, Inc., and Dighem, 1994, Filtered total field VLF contours of Nyac mining district: Public Data File PDF 94-17, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:63,360
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 63360
    Source_Contribution: Data collection, processing, and delivery

    Alaska Division of Geological & Geophysical Surveys and others, 1994 (source 4 of 9)
    Alaska Division of Geological & Geophysical Surveys, WGM, Inc., and Dighem, 1994, Flight lines of Nyac mining district: Public Data File PDF 94-16, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:63,360
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 63360
    Source_Contribution: Data collection, processing, and delivery

    Burns, L.E. and others, 2004 (source 5 of 9)
    Burns, L.E., Fugro Airborne Surveys Corp., and Stevens Exploration Management Corp., 2004, Line, gridded, and vector data, and selected plot files from the aeromagnetic survey of the Nyac mining district, central Alaska: Geophysical Report GPR 2004-4, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 DVD
    Type_of_Source_Media: paper
    Source_Contribution: Data collection, processing, and delivery

    DGGS Staff and others, 1994 (source 6 of 9)
    Staff, DGGS, Dighem, and WGM, Inc., 1994, CD-ROM digital archive files of 1993 survey data for Nome, Circle, Nyac, and Valdez Creek mining districts: Public Data File PDF 94-15, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 22 p., 1 DVD
    Type_of_Source_Media: paper
    Source_Contribution: Data collection, processing, and delivery

    DGGS Staff and others, 1994 (source 7 of 9)
    Staff, DGGS, WGM, Inc., and Dighem, 1994, Digital gridded data of total field magnetics for entire survey of Nyac mining district: Public Data File PDF 94-34, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 DVD
    Type_of_Source_Media: paper
    Source_Contribution: Data collection, processing, and delivery

    DGGS Staff and others, 1994 (source 8 of 9)
    Staff, DGGS, WGM, Inc., and Dighem, 1994, Total field magnetics of the Nyac mining district: Report of Investigation RI 94-3, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:63,360
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 63360
    Source_Contribution: Data collection, processing, and delivery

    McConnell, D.L., 1994 (source 9 of 9)
    McConnell, D.L., 1994, Final summary of 1993 airborne geophysical surveys of the Nome, Circle, Nyac, and Valdez Creek areas: Public Data File PDF 94-36, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 327 p., 4 sheets, scale 1:63,360
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 63360
    Source_Contribution: Data collection, processing, and delivery

  2. How were the data generated, processed, and modified?

    Date: 1993 (process 1 of 9)
    Data collection, processing, and delivery - The airborne geophysical data were acquired under contract with WGM Mining and Geological Consultants, Inc. and Dighem Surveys and Processing. The contractor's project report and other supporting documents are in the 'documents' digital data package. They provide detailed documentation of the system specifications, data collection, processing, and delivery.

    Data sources used in this process:

    • Alaska Division of Geological & Geophysical Surveys and others, 1994
    • Alaska Division of Geological & Geophysical Surveys and others, 1994
    • Alaska Division of Geological & Geophysical Surveys and others, 1994
    • Alaska Division of Geological & Geophysical Surveys and others, 1994
    • Burns, L.E. and others, 2004
    • DGGS Staff and others, 1994
    • DGGS Staff and others, 1994
    • DGGS Staff and others, 1994
    • McConnell, D.L., 1994

    Date: 2004 (process 2 of 9)
    Reformatting - Digital data collected in 1993 were reformatted for ease of use with modern processing tools, vector files were added, and new color maps were produced. No reprocessing was done.

    Date: 2019 (process 3 of 9)
    Grid development - The analytic signal grid was generated by using the analytic signal function in Geosoft Oasis Montaj v9 on 100m upward continued simulated total magnetic field grid. The calculated first vertical derivative grid was created during the analytic signal process. The derivatives in the analytic signal calculation were computed using a fast Fourier transform (FFT) based 2D filter.

    Date: 2019 (process 4 of 9)
    RGB GeoTiff creation - RGB GeoTIFF raster files of gridded data were exported using Geosoft v9 by loading each Geosoft grid onto a map and using the map export tool.

    Date: 2019 (process 5 of 9)
    DXF conversion and geographic referencing - Contractor provided AutoCAD DXF files were converted to an ESRI Geodatabase in ArcMap v10 using the CAD to Geodatabase tool.

    Date: 2019 (process 6 of 9)
    Standard Boundary Polygon - The final boundary polygon was generated by loading the line data in Geosoft Oasis Montaj v9. The channel MAG was gridded using the Minimum Curvature option with the following settings: grid cell size = 25, blanking distance = 800, cells to extend beyond data = 2. The polygon file was created using Grid Outline tool with edge resolution = 1. The polygon file was exported to ESRI shapefile.

    Date: 2019 (process 7 of 9)
    Keyhole markup language (kml) KMZ archive creation - Data were exported from Geosoft and ESRI ArcMap to kml format files and/or KMZ archives. These files were then combined and modified in Google Earth Pro to create the final KMZ file.

    Date: 2019 (process 8 of 9)
    Simulated Magnetic Total Field - In this publication's older products and documentation the magnetic data products have been referred to as Total Field Magnetics on the maps and the MAG channel in the line data and 'mag' as a filename abbreviation. The new term 'sim_magtf' has been created to rename and clarify that the data are not representative of the true total magnetic field as the IGRF values have been removed with a single average value added back to the entire dataset, resulting in the IGRF gradient being removed. The term simulated magnetic total field and the filename abbreviation 'sim_magtf' is now used to identify these magnetic data.

    Date: 2019 (process 9 of 9)
    Data cataloged for archival and publication - All files were renamed and placed in a standardized set of folders according to the DGGS Geophysics Data Management Manual. Where applicable and as needed data were converted to newer file formats and new files were created. Supporting documentation including but not limited to readme text files, maps, figures, survey overview report, missing data type explanations, and metadata were created.

  3. What similar or related data should the user be aware of?

    Staff, DGGS, 2014, Airborne GeophysWeb: A compilation of geophysical data from DGGS and cooperating agencies: Digital Data Series DDS 2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Geoterrex-Dighem, Surveys, Fugro Airborne, Stevens Exploration Management Corp., Pritchard, R.A., Burns, L.E., Emond, A.M., and Staff, DGGS, 2016, Sub-regional, merged, gridded airborne geophysical data: Digital Data Series DDS 12, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 DVD


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 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?

    These data are positioned with post-processed differential GPS.

  3. How accurate are the heights or depths?

    These data are positioned with post-processed differential GPS.

  4. Where are the gaps in the data? What is missing?

    This data set includes files that contain processed aeromagnetic measurements, electromagnetic 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 the same contract specifications for all data. 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 99709-3707
    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
  2. What's the catalog number I need to order this data set?

    GPR 2019-4

  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: 01-Apr-2019
Metadata author:
Alaska Division of Geological & Geophysical Surveys
Attn: Simone Montayne
Metadata Manager
3354 College Road
Fairbanks, AK 99709-3707
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:


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