Fortymile mining district electromagnetic and magnetic airborne geophysical survey, data compilation

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Frequently anticipated questions:


What does this data set describe?

Title:
Fortymile mining district electromagnetic and magnetic airborne geophysical survey, data compilation
Abstract:
The Fortymile electromagnetic and magnetic airborne geophysical survey data were acquired with a DIGHEM-V Electromagnetic (EM) system and a cesium magnetometer. The EM and magnetic sensors were flown at a height of 30 meters (m). In addition the survey recorded data from radar and laser altimeters, a GPS navigation system, 50/60 Hz monitors and a video camera. Flights were performed with an AS-350-B2 Squirrel helicopter at a mean terrain clearance of 60 m along N-S survey flight lines with a spacing of 400 m. Tie lines were flown perpendicular to the flight lines at intervals of approximately 4,800 m
Supplemental_Information:

Project Name:	Fortymile
Contracting Agency:	State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS)
DGGS Section:	Mineral Resources section
Program:	Alaska Airborne Geophysical/Geological Mineral Inventory Program
Funding Source:	Alaska State Legislature
Contractor:	Stevens Exploration Management Corp.
Survey Flown By:	CGG Geoterrex-Dighem now CGG (year 2015)
CGG Project Number:	659
DGGS Contract Manager:	Laurel E. Burns
Data Acquisition:	Digitally acquired
Line miles (km):	4753 miles (7648 km)
Data Acquisition:
Start Date (YYYY-MM-DD):	1998-08-18
End Date   (YYYY-MM-DD):	1998-09-10
Platform:	Helicopter
Platform: Model:	AS-350-B2 Squirrel
Survey Altitude Model:	Mean terrain clearance (height above ground)
Nominal Helicopter Height:	60 metres
Nominal Bird Height:	30 metres
Traverse: Line Azimuth:    	0 degrees / 180 degrees
Traverse: Line Spacing:	1/4 mile (400 m)
Tie: Line Azimuth:	90 degrees / 270 degrees
Tie: Line Spacing:	approximately 3 miles (approximately 4800 m)
Border lines:	present around all non-parallel and non-perpendicular edges
Magnetics: Magnetometer:   	Scintrex cesium sensor, mounted in bird
Electromagnetics: Sensor Model:	Dighem(V)
Navigation System: Sensor:	Global Positioning System
Navigation System: Sensor:	Ashtech/Racal Real-Time Differential Global Positioning System
Navigation System: Method:	Post-flight differential positioning
Additional equipment: 	Radar and laser altimeters, video camera, and 50/60 Hz monitors

Operating frequencies used for the Dighem (V) system.

August 18 to September 3, Flights 1 to 31
Cx900    1104 Hz   separation = 8 m
Cp900     877 Hz   separation = 8 m
Cx5500   5935 Hz   separation = 8 m
Cp7200   7180 Hz   separation = 8 m
Cp56k   56406 Hz   separation = 6.3 m

September 4 to September 10, Flights 32 to 49
Cx900    1104 Hz   separation = 8 m
Cp900     877 Hz   separation = 8 m
Cx5500   5946 Hz   separation = 8 m
Cp7200   7180 Hz   separation = 8 m
Cp56k   56406 Hz   separation = 6.3 m

FLIGHT AND LINE NAMING

Example: L11020:29082

L = L for transverse(production) T for tie(cross)
1 = Area
1 = Line number digit 1
0 = Line number digit 2
2 = Line number digit 3
0 = Reflight number
:
2 = System number digit 1
9 = System number digit 2
0 = Flight number digit 1
8 = Flight number digit 2
2 = Flight number digit 3

Example: T15021:3089

T = T for tie(cross) L for transverse(production)
1 = Area
5 = Line number digit 1
0 = Line number digit 2
2 = Line number digit 3
1 = Reflight number
:
3 = System number digit 1
0 = Flight number digit 1
8 = Flight number digit 2
9 = Flight number digit 3

  1. How should this data set be cited?

    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:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -148.699814
    East_Bounding_Coordinate: -148.238327
    North_Bounding_Coordinate: 65.642426
    South_Bounding_Coordinate: 65.361259

  3. What does it look like?

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

    Calendar_Date: 1998
    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: 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 .01
      Ordinates (y-coordinates) are specified to the nearest .01
      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?

    ascii_data
    ascii format final and raw data with readme files, ascii format gridded data, ascii EM anomalies (Source: Geoterrex-Dighem and Stevens Exploration Management Corp.)

    databases_geosoft
    Geosoft format database file with extension .gdb, Geosoft format import template with extension .iO for final ascii data (Source: Geoterrex-Dighem and Stevens Exploration Management Corp.)

    documents
    project report, portfolio summary report authored by DGGS (Source: Alaska Division of Geological & Geophysical Surveys (DGGS), Geoterrex-Dighem, and Stevens Exploration Management Corp.)

    grids_ermapper
    geographically registered gridded data, ErMapper ERS format (Source: Alaska Division of Geological & Geophysical Surveys (DGGS), Geoterrex-Dighem, and Stevens Exploration Management Corp.)

    grids_geosoft
    Geosoft-format binary grids, these grids can be viewed in ESRI ArcMap using a free plugin from Geosoft. Additional explanatory information is included with the download files (Source: Alaska Division of Geological & Geophysical Surveys (DGGS), Geoterrex-Dighem, and Stevens Exploration Management Corp.)

    images_registered
    GeoTiff format images of all gridded data. Additional explanatory information is included with the download files (Source: Alaska Division of Geological & Geophysical Surveys (DGGS), Geoterrex-Dighem, and Stevens Exploration Management Corp.)

    kmz
    Google Earth kmz files of of all gridded data (Source: Alaska Division of Geological & Geophysical Surveys (DGGS), Geoterrex-Dighem, and Stevens Exploration Management Corp.)

    maps_pdf_format
    print format maps in pdf format (Source: Alaska Division of Geological & Geophysical Surveys (DGGS), Geoterrex-Dighem, and Stevens Exploration Management Corp.)

    maps_prn_format
    print format maps in prn (printer file) format; 2015-05-15 version note: some maps no longer display the same as the original printed maps, additional explanatory information is included with the download files (Source: Alaska Division of Geological & Geophysical Surveys (DGGS), Geoterrex-Dighem, and Stevens Exploration Management Corp.)

    vector_data
    boundary polygon in vector format; line path, interpretation, data contours, EM anomalies, map surrounds, in ESRI file geodatabase, DXF and PLT format (Source: Alaska Division of Geological & Geophysical Surveys (DGGS), Geoterrex-Dighem, and Stevens Exploration Management Corp.)


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 for 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
    GIS Manager
    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?

The 1998 Fortymile airborne electromagnetic and magnetic geophysical survey and this compilation are part of the Alaska Airborne Geophysical/Geological Mineral Inventory project funded by the Alaska State Legislature and managed by State of Alaska, Department of Natural Resources (DNR), Division of Geological & Geophysical Surveys (DGGS). The project seeks to catalyze private-sector mineral development investment. Alaska State lands that: 1) have major economic value; 2) can be developed in the short term to provide high quality jobs for Alaska; and 3) will provide economic diversification to help offset the loss of Prudhoe Bay oil revenue. This purpose for this publication is to compile and upgrade key digital data into a single publication for online data distribution.


How was the data set created?

  1. From what previous works were the data drawn?

    Akima, H., 1970 (source 1 of 24)
    Akima, H., 1970, A new method of interpolation and smooth curve fitting based on local procedures: Journal of the Association of Computing Machinery v. 7, no. 4, Association for Computing Machinery, New York, NY, USA.

    Type_of_Source_Media: paper
    Source_Contribution: total magnetic field data

    Fraser, D.C., 1978 (source 2 of 24)
    Fraser, D.C., 1978, Resistivity mapping with an airborne multicoil electromagnetic system: Geophysics v. 43, Society of Exploration Geophysicists, Tulsa, OK, United States.

    Type_of_Source_Media: paper
    Source_Contribution: raw and processed point data along flight lines

    Burns, L.E., 1999 (source 3 of 24)
    Burns, L.E., 1999, Color scheme variations of the total field magnetics for part of the Fortymile mining district: Miscellaneous Publication MP 35, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:250,000
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 250000
    Source_Contribution: legacy data compilation

    Burns, L.E., 1999 (source 4 of 24)
    Burns, L.E., 1999, Different coplanar resistivities and color schemes for part of the Fortymile mining district: Miscellaneous Publication MP 36, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:250,000
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 250000
    Source_Contribution: legacy data compilation

    Burns, L.E. and others, 2015 (source 5 of 24)
    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: paper
    Source_Contribution: legacy data compilation

    Burns, L.E. and Liss, S.A., 1999 (source 6 of 24)
    Burns, L.E., and Liss, S.A., 1999, Portfolio of aeromagnetic and resistivity maps of part of the Fortymile mining district, Alaska, southern Eagle and northern Tanacross quadrangles: Public Data File PDF 99-6, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 20 p., 1 sheet
    Type_of_Source_Media: paper
    Source_Contribution: legacy data compilation

    DGGS Staff and others, 1999 (source 7 of 24)
    Staff, DGGS, Geoterrex-Dighem, and Stevens Exploration Management Corp., 1999, 1 CD-ROM containing gridded files and section line of 1998 geophysical survey data for part of the Fortymile and Livengood mining districts, Alaska, southern Eagle, northern Tanacross, and central Livengood quadrangles: Public Data File PDF 99-8, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 DVD
    Type_of_Source_Media: CD-ROM
    Source_Contribution: legacy data compilation

    DGGS Staff and others, 1999 (source 8 of 24)
    Staff, DGGS, Geoterrex-Dighem, and Stevens Exploration Management Corp., 1999, 7200 Hz coplanar resistivity of part of the Fortymile mining district, Alaska, southern Eagle and northern Tanacross quadrangles: Public Data File PDF 99-5, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 2 sheets, scale 1:63,360
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 63360
    Source_Contribution: legacy data compilation

    DGGS Staff and others, 1999 (source 9 of 24)
    Staff, DGGS, Geoterrex-Dighem, and Stevens Exploration Management Corp., 1999, 7200 Hz coplanar resistivity of part of the Fortymile mining district, Alaska, southern Eagle and northern Tanacross quadrangles: Report of Investigation RI 99-3, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 2 sheets, scale 1:63,360
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 63360
    Source_Contribution: legacy data compilation

    DGGS Staff and others, 1999 (source 10 of 24)
    Staff, DGGS, Geoterrex-Dighem, and Stevens Exploration Management Corp., 1999, 900 Hz coplanar resistivity of part of the Fortymile mining district, Alaska, southern Eagle and northern Tanacross quadrangles: Public Data File PDF 99-4, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 2 sheets, scale 1:63,360
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 63360
    Source_Contribution: legacy data compilation

    DGGS Staff and others, 1999 (source 11 of 24)
    Staff, DGGS, Geoterrex-Dighem, and Stevens Exploration Management Corp., 1999, 900 Hz coplanar resistivity of part of the Fortymile mining district, Alaska, southern Eagle and northern Tanacross quadrangles: Report of Investigation RI 99-2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 2 sheets, scale 1:63,360
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 63360
    Source_Contribution: legacy data compilation

    DGGS Staff and others, 1999 (source 12 of 24)
    Staff, DGGS, Geoterrex-Dighem, and Stevens Exploration Management Corp., 1999, CD-ROM containing profile and gridded data and section lines of the 1998 geophysical survey data for part of the Fortymile mining district, Alaska, southern Eagle and northern Tanacross quadrangles: Public Data File PDF 99-9, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 DVD
    Type_of_Source_Media: CD-ROM
    Source_Contribution: legacy data compilation

    DGGS Staff and others, 1999 (source 13 of 24)
    Staff, DGGS, Geoterrex-Dighem, and Stevens Exploration Management Corp., 1999, Flight lines of part of the Fortymile mining district, Alaska, southern Eagle and northern Tanacross quadrangles: Public Data File PDF 99-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 2 sheets, scale 1:63,360
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 63360
    Source_Contribution: legacy data compilation

    DGGS Staff and others, 1999 (source 14 of 24)
    Staff, DGGS, Geoterrex-Dighem, and Stevens Exploration Management Corp., 1999, Total field magnetics and detailed electromagnetic anomalies of part of the Fortymile mining district, Alaska, southern Eagle and northern Tanacross quadrangles (Eagle A-1): Public Data File PDF 99-10E, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:31,680
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 31680
    Source_Contribution: legacy data compilation

    DGGS Staff and others, 1999 (source 15 of 24)
    Staff, DGGS, Geoterrex-Dighem, and Stevens Exploration Management Corp., 1999, Total field magnetics and detailed electromagnetic anomalies of part of the Fortymile mining district, Alaska, southern Eagle and northern Tanacross quadrangles (Eagle A-2): Public Data File PDF 99-10D, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:31,680
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 31680
    Source_Contribution: legacy data compilation

    DGGS Staff and others, 1999 (source 16 of 24)
    Staff, DGGS, Geoterrex-Dighem, and Stevens Exploration Management Corp., 1999, Total field magnetics and detailed electromagnetic anomalies of part of the Fortymile mining district, Alaska, southern Eagle and northern Tanacross quadrangles (eastern Eagle A-3): Public Data File PDF 99-10C, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:31,680
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 31680
    Source_Contribution: legacy data compilation

    DGGS Staff and others, 1999 (source 17 of 24)
    Staff, DGGS, Geoterrex-Dighem, and Stevens Exploration Management Corp., 1999, Total field magnetics and detailed electromagnetic anomalies of part of the Fortymile mining district, Alaska, southern Eagle and northern Tanacross quadrangles (northern Tanacross D-1): Public Data File PDF 99-10G, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:31,680
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 31680
    Source_Contribution: legacy data compilation

    DGGS Staff and others, 1999 (source 18 of 24)
    Staff, DGGS, Geoterrex-Dighem, and Stevens Exploration Management Corp., 1999, Total field magnetics and detailed electromagnetic anomalies of part of the Fortymile mining district, Alaska, southern Eagle and northern Tanacross quadrangles (northern Tanacross D-2): Public Data File PDF 99-10F, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:31,680
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 31680
    Source_Contribution: legacy data compilation

    DGGS Staff and others, 1999 (source 19 of 24)
    Staff, DGGS, Geoterrex-Dighem, and Stevens Exploration Management Corp., 1999, Total field magnetics and detailed electromagnetic anomalies of part of the Fortymile mining district, Alaska, southern Eagle and northern Tanacross quadrangles (northwestern Eagle A-3, part of A-4): Public Data File PDF 99-10B, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:31,680
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 31680
    Source_Contribution: legacy data compilation

    DGGS Staff and others, 1999 (source 20 of 24)
    Staff, DGGS, Geoterrex-Dighem, and Stevens Exploration Management Corp., 1999, Total field magnetics and detailed electromagnetic anomalies of part of the Fortymile mining district, Alaska, southern Eagle and northern Tanacross quadrangles (western part of Eagle B-3): Public Data File PDF 99-10A, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:31,680
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 31680
    Source_Contribution: legacy data compilation

    DGGS Staff and others, 1999 (source 21 of 24)
    Staff, DGGS, Geoterrex-Dighem, and Stevens Exploration Management Corp., 1999, Total field magnetics and electromagnetic anomalies of part of the Fortymile mining district, Alaska, southern Eagle and northern Tanacross quadrangles (clear diazo film version): Public Data File PDF 99-3, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 2 sheets, scale 1:63,360
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 63360
    Source_Contribution: legacy data compilation

    DGGS Staff and others, 1999 (source 22 of 24)
    Staff, DGGS, Geoterrex-Dighem, and Stevens Exploration Management Corp., 1999, Total field magnetics and electromagnetic anomalies of part of the Fortymile mining district, Alaska, southern Eagle and northern Tanacross quadrangles: Public Data File PDF 99-2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 2 sheets, scale 1:63,360
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 63360
    Source_Contribution: legacy data compilation

    DGGS Staff and others, 1999 (source 23 of 24)
    Staff, DGGS, Geoterrex-Dighem, and Stevens Exploration Management Corp., 1999, Total field magnetics of part of the Fortymile mining district, Alaska, southern Eagle and northern Tanacross quadrangles: Report of Investigation RI 99-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 2 sheets, scale 1:63,360
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 63360
    Source_Contribution: legacy data compilation

    Pritchard, R.A. and Geoterrex-Dighem, 1999 (source 24 of 24)
    Pritchard, R.A., and Geoterrex-Dighem, 1999, Project report of the 1998 geophysical survey data of part of the Fortymile mining district, Alaska, southern Eagle and northern Tanacross quadrangles: Public Data File PDF 99-7, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 162 p., 2 sheets, scale 1:63,360
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 63360
    Source_Contribution: legacy data compilation

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

    Date: 1998 (process 1 of 12)
    Raw and processed point data along flight lines - These data are directly provided by the contractor. Raw data are a direct export from field collection instruments. Final data are processed by method according to the contractor provided reports and process steps in this document.

    Data sources used in this process:

    • Fraser, D.C., 1978

    Date: 1998 (process 2 of 12)
    Geophysical data - The geophysical data were acquired with a DIGHEM-V Electromagnetic (EM) system, a cesium magnetometer, and a Herz VLF system installed in on AS350B-2 Squirrel helicopter. In addition, the survey recorded data from a radar altimeter, GPS navigation system, 50/60 Hz monitors and video camera.

    Date: 1998 (process 3 of 12)
    Total magnetic field data - The total magnetic field data were acquired with a sampling interval of 0.1 seconds, and were (1) corrected for diurnal variations by subtraction of the digitally recorded base station magnetic data, (2) leveled to the tie line data, and (3) interpolated onto a regular 100 m grid using a modified Akima (1970) technique. The regional variation (or IGRF values, 1995, updated to September, 1998) was removed, then the average IGRF value was added back to the leveled magnetic data creating the final simulated total magnetic field data. The aeromagnetic data were interpolated onto a regular 100 m grid using a modified Akima (1970) technique.

    Data sources used in this process:

    • Akima, H., 1970

    Date: 1998 (process 4 of 12)
    Inphase and quadrature components - The DIGHEM-V EM system measured inphase and quadrature components at five frequencies. EM data were sampled at 0.1 second intervals. The EM inphase and quadrature data were drift corrected using base level data collected at high altitude (areas of no signal). Along-line filters were applied to the data to remove spheric spikes. The data were inspected for variations in phase, and a phase correction was applied to the data if necessary. Resistivities were then calculated from the inphase and quadrature data for all frequencies based on a pseudo-layer half-space model. Manual leveling of the inphase and quadrature of each coil pair, based on the resistivity data and comparisons to the data from the other frequencies, was performed. Automated micro-leveling was carried out in areas of low signal. The EM system responds to bedrock conductors, conductive overburden, and cultural sources. The power line monitors and the flight track video were examined to locate cultural sources. The EM anomalies that are indicated are classified by conductance. These anomalies are described in files '*_emanomalies.csv' and '*_projectreport.pdf.'

    Date: 1998 (process 5 of 12)
    Vector data in dxf, dwg, plt, and att file formats - vector data (examples: line path, data contours) were created by exporting data and interpretations to vector format.

    Date: 1998 (process 6 of 12)
    Project report, portfolio report, and other important documents - The project report, portfolio report, and other important documents were generated by the contractor, DGGS staff, or a combination.

    Date: 2015 (process 7 of 12)
    Legacy data compilation - DGGS staff compiled and organized previously published data and the originating data from the contractor. DGGS staff converted select hpp files into PDFs to complete the PDF map collection. Original vector data were compiled into an ESRI ArcMap File Geodatabase using ArcMap 10.2.2's CAD to Geodatabase tool in batch mode. 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 MAGIGRF channel in the line data and 'tfm' 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 IGRF value added back to the data, resulting in the IGRF gradient being removed. The term simulated magnetic total field and the filename abbreviation 'sim_magtf' is now used to identify the final magnetic data.

    Data sources used in this process:

    • Burns, L.E., 1999
    • Burns, L.E., 1999
    • Burns, L.E. and others, 2015
    • Burns, L.E. and Liss, S.A., 1999
    • DGGS Staff and others, 1999
    • DGGS Staff and others, 1999
    • DGGS Staff and others, 1999
    • DGGS Staff and others, 1999
    • DGGS Staff and others, 1999
    • DGGS Staff and others, 1999
    • DGGS Staff and others, 1999
    • DGGS Staff and others, 1999
    • DGGS Staff and others, 1999
    • DGGS Staff and others, 1999
    • DGGS Staff and others, 1999
    • DGGS Staff and others, 1999
    • DGGS Staff and others, 1999
    • DGGS Staff and others, 1999
    • DGGS Staff and others, 1999
    • DGGS Staff and others, 1999
    • DGGS Staff and others, 1999
    • Pritchard, R.A. and Geoterrex-Dighem, 1999

    Date: 2015 (process 8 of 12)
    Data in Geosoft GDB format - These data were created by importing the final ascii data into Geosoft Oasis Montaj v8.3 using the provided *.iO import file.

    Date: 2015 (process 9 of 12)
    Geographically registered gridded data in Geosoft GRD format - DGGS assigned missing projection info to grids as needed using Geosoft Oasis montaj v8.3. Geosoft Oaisis montaj MAGMAP extension was used to create analytic signal and calculated first vertical derivative grids.

    Date: 2015 (process 10 of 12)
    Geographically registered gridded data in GeoTiff format - These data were created by DGGS using Geosft Oasis montaj v8.3. Geosoft grd files were displayed in Geosoft and exported to GeoTiff. A matching colorbar for each grid was displayed in Geosoft and export as a GeoTiff. ER Mapper ERS files were created using Geosoft Oasis montaj v8.3 grid copy/convert function from the Geosoft format grids.

    Date: 2015 (process 11 of 12)
    Google Earth KMZ files - Created Google Earth KMZ files from the GeoTiff format gridded data using ESRI ArcMap 10.2.2.

    Date: 2015 (process 12 of 12)
    Boundary polygon - The boundary polygon was generated by loading the final line data in Geosoft Oasis montaj v8.3. The final magnetic data was gridded using the Minimum Curvature option with the following settings: grid cell size = 1/5 of line spacing, blanking distance = double the line spacing, cells to extend beyond data = 0. The polygon file was created using Grid Outline tool with edge resolution = 1. The polygon file was exported to ERSI shapefile.

  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?

    
    Apparent resistivity cutoffs:
    900 Hz coplanar apparent resistivity cutoff 1008 Ohm-m
    7200 Hz coplanar apparent resistivity cutoff 8250 Ohm-m
    
    Electromagnetic system sensitivity:
    Frequency; Coil Orientation; Sensitivity (ppm)
     900 Hz      horizontal coplanar    0.06
     1000 Hz     vertical coaxial       0.06
     5500 Hz     vertical coaxial       0.10
     7200 Hz     horizontal coplanar    0.10
     56,000 Hz   horizontal coplanar    0.30
    
    Magnetic system sensitivity: 0.01 nT
    
    
    

  2. How accurate are the geographic locations?

    Positional accuracy of the presented data is better than 10 m with respect to the UTM grid.

  3. How accurate are the heights or depths?

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

    Missing magnetic values occur in the databases for the survey area because of the lagging process at the beginning of some lines and due to despiking. Slow airspeed over steep terrain can cause rapid bird swing and magnetic data spikes that require removal from final data. Missing values in the calculated 'depth' occur where altimeter limits for resistivity calculation are exceeded or where magnetite causes inphase to be negative. Missing apparent resistivity values are generally caused by altitude exceeding the tolerance for meaningful resistivity calculation.

  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 except the KMZ files, which utilize WGS84 geographic coordinates. In some cases we provide values in both UTM NAD27 and geographic WGS84 projections.


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?

    GPR 2015-4

  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?

  5. What hardware or software do I need in order to use the data set?

    Requisite software varies according to the file format. Possible software requirements include, but are not limited to: Geosoft Oasis montaj (full version and viewer), INTREPID geophysical software, ESRI Arc GIS products, MapInfo, Global Mapper, UltraEdit, NotePad ++, Microsoft Office or open source office software, Adobe Reader, Lerup PrintFile, Google Earth, ER Mapper


Who wrote the metadata?

Dates:
Last modified: 05-Jun-2015
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:


Generated by mp version 2.9.21 on Fri Jun 5 13:41:56 2015