Sub-regional, merged, gridded airborne geophysical data

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Frequently anticipated questions:


What does this data set describe?

Title: Sub-regional, merged, gridded airborne geophysical data
Abstract:
Merged grids of residual magnetic intensity, digital terrain model, and apparent resistivity compiled from the Tok, Ladue, Slate Creek - Slana River, Alaska Highway Corridor, and Fortymile geophysical surveys.
Supplemental_Information:
tok_lad_scsr_ahc_40mi:    Geosoft-format binary grids, GeoTiff format gridded data images, KMZ/KML files, Geosoft ASCII polygon files (PLY), Geosoft ASCII zone files, ESRI Shapefiles; note: these data are provided in both UTM NAD27 and Geographic WGS84 projections. The data files were compiled from the Tok, Ladue, Slate Creek - Slana River, Alaska Highway Corridor, and Fortymile geophysical surveys.
  1. How should this data set be cited?

    Pritchard, R.A., CGG, 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:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -145.59524
    East_Bounding_Coordinate: -140.84782
    North_Bounding_Coordinate: 64.47524
    South_Bounding_Coordinate: 62.39953

  3. What does it look like?

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

    Beginning_Date: 1998
    Ending_Date: 2014
    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 North American Datum of 1927.
      The ellipsoid used is Clarke 1866.
      The semi-major axis of the ellipsoid used is 6378206.4.
      The flattening of the ellipsoid used is 1/294.9786982.

  7. How does the data set describe geographic features?

    tok_lad_scsr_ahc_40mi
    Geosoft-format binary grids, GeoTiff format gridded data images, KMZ/KML files, Geosoft ASCII polygon files (PLY), Geosoft ASCII zone files, ESRI Shapefiles; note: these data are provided in both UTM NAD27 and Geographic WGS84 projections. The data files were compiled from the Tok, Ladue, Slate Creek - Slana River, Alaska Highway Corridor, and Fortymile geophysical surveys. (Source: Alaska Division of Geological & Geophysical Surveys (DGGS) and contractor.)


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 for the originating geophysical surveys was provided by the Alaska Division of Geological & Geophysical Surveys' (DGGS) Airborne Geophysical/Geological Mineral Inventory (AGGMI) program and Strategic and Critical Minerals Assessment Capital Improvement Project. The geophysical surveys were managed by State of Alaska, Department of Natural Resources (DNR), Division of Geological & Geophysical Surveys (DGGS). The survey data were collected and processed by CGG, Fugro Airborne Surveys Corp., and Geoterrex-Dighem.

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

    Alaska Division of Geological & Geophysical Surveys
    Geophysics Staff
    3354 College Road
    Fairbanks, AK 99709-3707
    USA

    (907)451-5020 (voice)
    dggsgis@alaska.gov

    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays


Why was the data set created?

This electromagnetic and magnetic airborne geophysical survey data compilation is a product of the Alaska Division of Geological & Geophysical Surveys' (DGGS) Airborne Geophysical/Geological Mineral Inventory (AGGMI) program and the Alaska Strategic and Critical Minerals Assessment Capital Improvement Project. The goal of the Alaska Division of Geological & Geophysical Surveys' (DGGS) Airborne Geophysical/Geological Mineral Inventory (AGGMI) program is to enhance the understanding of Alaska's mineral resources and stimulate private-sector mineral development. The program seeks to delineate mineral zones on Alaska State lands that: (1) have major economic value; (2) can be developed in the short term to provide high-quality jobs for Alaskans; and (3) will provide economic diversification to help offset the loss of Prudhoe Bay oil revenue. Candidate lands for this program are identified on the basis of existing geologic knowledge, land ownership, and nominations from Alaska's geologic community. The AGGMI program and resulting new geologic knowledge are recognized worldwide and have encouraged millions of dollars of venture capital expenditures in the local economies of the surveyed mining districts. These venture capital expenditures have led to discovery and delineation of new mineral resources. The multi-year Strategic and Critical Minerals Assessment Capital Improvement Project (SCMA) was established to determine Alaska's geologic potential for rare-earth elements and other minerals that are essential for our modern, technology-based society. This program began in FY2012 with a data survey and compilation of existing information on rare-earth-element occurrences in Alaska, and expanded significantly in FY2013 to include additional critical minerals, re-analyses of existing samples, and obtaining new field and analytical data, including airborne geophysics.


How was the data set created?

  1. From what previous works were the data drawn?

    Burns, L.E. and others, 2006 (source 1 of 5)
    Burns, L.E., Fugro Airborne Surveys Corp., and Stevens Exploration Management Corp., 2006, Line, grid, and vector data, and plot files for the airborne geophysical survey of the Alaska Highway corridor, east-central Alaska: Geophysical Report GPR 2006-6, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 DVD
    Type_of_Source_Media: digital data
    Source_Contribution: gridded data

    Burns, L.E. and others, 2009 (source 2 of 5)
    Burns, L.E., Fugro Airborne Surveys Corp., and Stevens Exploration Management Corp., 2009, Line, grid, and vector data, and maps for the airborne geophysical survey of the Slate Creek-Slana River Survey, Chistochina mining district, south-central Alaska: Geophysical Report GPR 2009-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 18 sheets, 1 DVD, scale 1:63,360
    Type_of_Source_Media: digital data
    Source_Scale_Denominator: 63360
    Source_Contribution: gridded data

    Burns, L.E. and others, 2015 (source 3 of 5)
    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:

    Type_of_Source_Media: digital data
    Source_Contribution: gridded data

    Emond, A.M. and others, 2015 (source 4 of 5)
    Emond, A.M., CGG, Burns, L.E., Graham, G.R.C., and (US), CGG Land Inc., 2015, Tok electromagnetic and magnetic airborne geophysical survey data compilation: Geophysical Report GPR 2015-2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Type_of_Source_Media: digital data
    Source_Contribution: gridded data

    Burns, L.E. and others, 2011 (source 5 of 5)
    Burns, L.E., Fugro Airborne Surveys Corp., and Fugro GeoServices, Inc., 2011, Ladue survey area: Magnetic and electromagnetic line, grid, and vector data and Maps, Fortymile mining district, Tanacross Quadrangle, eastern Alaska: Geophysical Report GPR 2011-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 26 sheets, 1 DVD, scale 1:63,360
    Type_of_Source_Media: digital data
    Source_Scale_Denominator: 63360
    Source_Contribution: gridded data

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

    Date: 2011 (process 1 of 3)
    Gridded data - The gridded data from the Tok survey area (flown in 2014) were merged with data from previous surveys, the Fortymile survey block, flown in 1998, the Alaska Highway corridor survey, flown in 2005 and 2006, the Slana survey area, flown in 2008, and the Ladue Area, flown in 2010. The merges were completed using proprietary CGG ATLAS software techniques. ATLAS has the capability to merge or stitch numerous grids together. The process requires overlap between adjacent grid areas. There is also the option of selecting different grid stitch techniques. For this project the RMI and DTM grids were levelled to each other prior to merging. All parameters were merged together using a systematic technique. This method uses polynomial correction up to order 4 to the input grids and the base (preferred or primary grid). The coefficients are calculated using the overlapping area of all grids. Each of the grids is adjusted systematically for a fit with the preferred (base) grid and also for a fit with respect to each other. The process requires selecting a "master" grid or the grid that all other grids will be levelled to. The grid from the most recent survey was selected as the primary grid. Because the RMI and DTM grids were levelled to each other prior to merging, the simplest option of no datum shift of the grids was used. The nature of the resistivity parameter requires no levelling of the grids to each other before using the no datum shift option for final merging. The gridded data for the 2008 Slana survey were originally displayed in NAD27 Alaska, UTM Zone 6N. The data were re-projected into NAD27 Alaska, UTM Zone 7N using Oasis Montaj software before merging with the rest of the survey areas. A merge of the residual magnetic data was possible for all areas. DTM data were not available for the Fortymile survey block, therefore the DTM data were only merged with the Alaska Highway corridor, Slana and Ladue survey data. Because the electromagnetic data were collected using the DIGHEM system for Ladue, and the RESOLVE system for the Alaska Highway corridor survey, only one 'common' frequency existed between the two datasets. A merged grid of the 7200 Hz resistivity data from the Ladue block, and the 8200 resistivity data from the corridor survey was produced. When the Ladue data was merged in 2011 with the Fortymile survey data, although both the Ladue and Fortymile surveys were flown with the DIGHEM system, the resistivity data for the two surveys were not merged. In the time since the Fortymile survey was flown in 1998, acquisition and processing methods have changed and improved to the point where the Fortymile resistivity data would have had to undergo some re-processing in order to merge with the resistivity parameters from the Ladue survey. This was not within the scope of the Ladue contract, and no attempt was made to merge the Fortymile resistivity data. The merged resistivity data, therefore, consists of the previously merged Ladue/Alaska Highway corridor 7200/8200 Hz resistivity grid merged with the re-projected Slana 7200 Hz resistivity data and the present Tok 7200 Hz resistivity data. The resistivity for the Slana area was recalculated with higher upper limits of apparent resistivity, which are now used in processing more recent datasets.

    Data sources used in this process:

    • Burns, L.E. and others, 2006
    • Burns, L.E. and others, 2009
    • Burns, L.E. and others, 2015
    • Emond, A.M. and others, 2015
    • Burns, L.E. and others, 2011

    Date: 2015 (process 2 of 3)
    Boundary - DGGS staff constructed a boundary of the merged grid file. The gid boundary was constructed using Geosoft Oaisis montaj grid outline and map export functions. The boundary file is available in Geosft PLY ASCII format and ESRI Shapefile format.

    Date: 2016 (process 3 of 3)
    Google Earth KMZ files - DGGS staff created Google Earth KMZ/KML files from the grid files data using ESRI ArcGIS software.

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

    Geological Survey of Canada, and U.S. Geological Survey, 2015, Yukon - Eastern Alaska magnetic grid: Natural Resources Canada, Canada.

    Online Links:


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

  1. How well have the observations been checked?

    All originating data met contract specifications with a few exceptions due to difficult operational conditions. These exceptions did not noticeably impact data quality. Additional detail about contract specifications and operational issues can be found in the metadata of the originating surveys.

  2. How accurate are the geographic locations?

    All originating data were positioned by DGPS with an accuracy of 5 meters or better.

  3. How accurate are the heights or depths?

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

    Helicopter and fixed wing geophysical surveys often have small data gaps that do not negatively impact the overall quality of the final products. Reference the metadata for each originating survey for specific details.

  5. How consistent are the relationships among the observations, including topology?

    These data originate from multiple similar geophysical surveys with different specifications. Reference the metadata of each originating survey for exact specifications.


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
    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
    Contact_Instructions:
    Please view our website (<http://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?

    DDS 12

  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: 24-Feb-2016
Metadata author:
Alaska Division of Geological & Geophysical Surveys
Metadata Manager
3354 College Road
Fairbanks, AK 99709-3707
USA

(907)451-5020 (voice)

Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:


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