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

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Frequently anticipated questions:


What does this data set describe?

Title:
Petersville mining district electromagnetic and magnetic airborne geophysical survey, data compilation
Abstract:
This publication, GPR 2015-3, contains geophysical data produced from airborne surveys conducted in 1996 and released in 1997 for 415 sq miles of the Petersville mining district, Alaska by the Alaska Division of Geological & Geophysical Surveys (DGGS). Aeromagnetic and electromagnetic data were acquired during the helicopter-based surveys. During 2004, the same digital data were reformatted for ease of use with modern processing tools, vector files and the 56,000 Hz resistivity grid, were added, and new color maps were produced. Except for leveling of the 56,000 Hz coplanar resistivity grid, no reprocessing of the geophysical data was done. The files represent the end part of the 2004 process. A few maps produced in 1997, such as flight line maps and resistivity maps produced as bluelines, are not reproduced; however, color versions of these data and the data enabling production of these maps are included in this archive. Data provided in GPR 2015-3 include processed (1) linedata ASCII databases, (2) gridded files of magnetic and resistivity data, (3) vector files of data contours, interpreted electromagnetic anomalies, and flight lines, and (4) plot files of selected full-color maps, and (5) an Adobe Acrobat file showing the 56,000 Hz gridded data. A vector file of the interpretation overlay produced by the Contractor for the Petersville data (released previously on paper as DGGS Public Data File 97-8) is also included. All maps produced during 2004 are at a scale of 1:63,360 and are included in HPGL2 (*.prn), Adobe Acrobat (.pdf), and postscript (*.ps) format.
Supplemental_Information:
Project Name:  Petersville
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:   WGM, Mining and Geological Consultants, Inc.
Survey Flown By:       DIGHEM, a division of CGG Canada LTD.
CGG Project Number:    631 (two area job - Petersville and Chulitna)
DGGS Contract Manager: Laurel E. Burns
Data Acquisition:      Digitally acquired
Line miles (km):       3490 miles (5616 km)
Data Acquisition:
Start Date (YYYY-MM-DD):       1996-10-01
End Date   (YYYY-MM-DD):       1996-10-08
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:        90 degrees / 270 degrees
Traverse: Line Spacing:        1/4 mile (400 m)
Tie: Line Azimuth:     0 degrees / 180 degrees
Tie: Line Spacing:     approximately 3 miles (approximately 4800 m)
Magnetics: Magnetometer:       Picodas3340 optically pumped cesium sensor, towed in bird 20 M below helicopter
Electromagnetics: Sensor Model:     DIGHEM-V
Navigation System: Sensor:     Sercel NR106 Real-Time Differential Global Positioning System
Navigation System: Method:     Post-flight differential positioning
Additional equipment: magnetic base station, analog recorder, radar altimeter, digital data acquisition system, video camera, Dighem field workstation, and 50/60 Hz monitors

Operating frequencies used for the Dighem-V system.

September 24 - October 1, Flights 60 to 67
Cx900     898 Hz   separation = 8 m
Cp900    1010 Hz   separation = 8 m
Cx5500   6491 Hz   separation = 8 m
Cp7200   7216 Hz   separation = 8 m
Cp56k   56598 Hz   separation = 6.3 m

October 2 to October 10, Flights 68 to 87
Cx900    1042 Hz   separation = 8 m
Cp900     868 Hz   separation = 8 m
Cx5500   6491 Hz   separation = 8 m
Cp7200   7216 Hz   separation = 8 m
Cp56k   56598 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., Fugro Airborne Surveys Corp., Stevens Exploration Management Corp., and Graham, G.R.C., 2015, Petersville mining district electromagnetic and magnetic airborne geophysical survey, data compilation: Geophysical Report GPR 2015-3, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -151.66
    East_Bounding_Coordinate: -150.61
    North_Bounding_Coordinate: 62.64
    South_Bounding_Coordinate: 62.31

  3. What does it look like?

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

    Beginning_Date: 1996
    Ending_Date: 2015
    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: 5
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -153
      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 (Source: Fugro Airborne Surveys Corp. 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: Fugro Airborne Surveys Corp. and Stevens Exploration Management Corp.)

    documents
    Project report, portfolio summary report authored by DGGS, EM anomalies in ascii CSV format (Source: Alaska Division of Geological & Geophysical Surveys (DGGS), Fugro Airborne Surveys Corp. and Stevens Exploration Management Corp.)

    grids_ermapper
    Geographically registered gridded data, ErMapper ERS format (Source: Alaska Division of Geological & Geophysical Surveys (DGGS), Fugro Airborne Surveys Corp. 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), Fugro Airborne Surveys Corp. 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), Fugro Airborne Surveys Corp. and Stevens Exploration Management Corp.)

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

    maps_pdf_format
    Print format maps in pdf format (Source: Alaska Division of Geological & Geophysical Surveys (DGGS), Fugro Airborne Surveys Corp. and Stevens Exploration Management Corp.)

    maps_prn_format
    Print format maps in HPGL/2 printer file format with extension .prn. (Source: Alaska Division of Geological & Geophysical Surveys (DGGS), Fugro Airborne Surveys Corp. and Stevens Exploration Management Corp.)

    maps_ps_format
    Print format maps in ps (postscript) format (Source: Alaska Division of Geological & Geophysical Surveys (DGGS), Fugro Airborne Surveys Corp. and Stevens Exploration Management Corp.)

    vector_data
    line path, data contours, and survey boundary in ESRI shape file (SHP) and Autocad (2000) DXF formats (Source: Alaska Division of Geological & Geophysical Surveys (DGGS), Fugro Airborne Surveys Corp. 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 for this survey was provided by the Alaska Division of Geological & Geophysical Surveys' (DGGS) Airborne Geophysical/Geological Mineral Inventory (AGGMI) and Strategic and Critical Minerals Assessment Capital Improvement programs and managed by State of Alaska, Department of Natural Resources (DNR), Division of Geological & Geophysical Surveys (DGGS). The survey data was collected and processed by CGG.

  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 1996 Petersville survey and this current project 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. The project delineates 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 Alaska; and (3) will provide economic diversification to help offset the loss of Prudhoe Bay oil revenue. The purpose of the 2004 project was to upgrade the digital data formats and improve the map formats for the early detailed airborne geophysical surveys produced by DGGS as part of the Alaska Airborne Geophysical/Geological Mineral Inventory project and to provide these improved products to the public. Various items, such as color geophysical maps produced with raster topography, were not technically possible at time of the original data release. Various other digital files of use to the customer were also not accessible to the public for the older surveys.


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., 1997 (source 3 of 24)
    Burns, L.E., 1997, Portfolio of aeromagnetic and resistivity maps of the Petersville mining district, Alaska: Public Data File PDF 97-15, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 13 p
    Type_of_Source_Media: paper
    Source_Contribution: legacy data compilation

    Burns, L.E. and others, 2005, 0 p. (source 4 of 24)
    Burns, L.E., Fugro Airborne Surveys Corp., and Stevens Exploration Management Corp., 2005, 7200 Hz coplanar apparent resistivity of the Petersville mining district, Alaska: Geophysical Report GPR 2004-9-2A, 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: legacy data compilation

    Burns, L.E. and others, 2005, 0 p. (source 5 of 24)
    Burns, L.E., Fugro Airborne Surveys Corp., and Stevens Exploration Management Corp., 2005, 7200 Hz coplanar apparent resistivity of the Petersville mining district, Alaska: Geophysical Report GPR 2004-9-2B, 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: legacy data compilation

    Burns, L.E. and others, 2005, 0 p. (source 6 of 24)
    Burns, L.E., Fugro Airborne Surveys Corp., and Stevens Exploration Management Corp., 2005, 900 Hz coplanar apparent resistivity of the Petersville mining district, Alaska: Geophysical Report GPR 2004-9-3A, 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: legacy data compilation

    Burns, L.E. and others, 2005, 0 p. (source 7 of 24)
    Burns, L.E., Fugro Airborne Surveys Corp., and Stevens Exploration Management Corp., 2005, 900 Hz coplanar apparent resistivity of the Petersville mining district, Alaska: Geophysical Report GPR 2004-9-3B, 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: legacy data compilation

    Burns, L.E. and others, 2005 (source 8 of 24)
    Burns, L.E., Fugro Airborne Surveys Corp., and Stevens Exploration Management Corp., 2005, Line, gridded, and vector data, and selected plot files of the Petersville mining district, Alaska: Geophysical Report GPR 2004-9, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 DVD
    Type_of_Source_Media: paper
    Source_Contribution: legacy data compilation

    Burns, L.E. and others, 2005, 0 p. (source 9 of 24)
    Burns, L.E., Fugro Airborne Surveys Corp., and Stevens Exploration Management Corp., 2005, Total magnetic field of the Petersville mining district, Alaska: Geophysical Report GPR 2004-9-1A, 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: legacy data compilation

    Burns, L.E. and others, 2005, 0 p. (source 10 of 24)
    Burns, L.E., Fugro Airborne Surveys Corp., and Stevens Exploration Management Corp., 2005, Total magnetic field of the Petersville mining district: Geophysical Report GPR 2004-9-1B, 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: legacy data compilation

    DGGS Staff and others, 1997 (source 11 of 24)
    Staff, DGGS, Dighem, and WGM, Inc., 1997, 7200 Hz resistivity contours of the Petersville mining district, Alaska: Public Data File PDF 97-12, 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: legacy data compilation

    DGGS Staff and others, 1997 (source 12 of 24)
    Staff, DGGS, Dighem, and WGM, Inc., 1997, 7200 Hz resistivity contours of the Petersville mining district, Alaska: Report of Investigation RI 97-8, 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: legacy data compilation

    DGGS Staff and others, 1997 (source 13 of 24)
    Staff, DGGS, Dighem, and WGM, Inc., 1997, 900 Hz resistivity contours of the Petersville mining district, Alaska: Public Data File PDF 97-11, 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: legacy data compilation

    DGGS Staff and others, 1997 (source 14 of 24)
    Staff, DGGS, Dighem, and WGM, Inc., 1997, 900 Hz resistivity contours of the Petersville mining district, Alaska: Report of Investigation RI 97-7, 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: legacy data compilation

    DGGS Staff and others, 1997 (source 15 of 24)
    Staff, DGGS, Dighem, and WGM, Inc., 1997, CD-ROM digital archive files of 1996 survey data for Chulitna and Petersville mining districts, Alaska: Public Data File PDF 97-5, 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, 1997 (source 16 of 24)
    Staff, DGGS, Dighem, and WGM, Inc., 1997, Diazo film version of RI 97-5: Total field magnetics and electromagnetic anomalies of the Petersville mining district, Alaska: Public Data File PDF 97-10, 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: legacy data compilation

    DGGS Staff and others, 1997 (source 17 of 24)
    Staff, DGGS, Dighem, and WGM, Inc., 1997, Disk containing gridded files and section lines of the 1996 geophysical survey data for Petersville mining district: Public Data File PDF 97-14, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 DVD
    Type_of_Source_Media: paper
    Source_Contribution: legacy data compilation

    DGGS Staff and others, 1997 (source 18 of 24)
    Staff, DGGS, Dighem, and WGM, Inc., 1997, Flight line maps of the Petersville mining district, Alaska: Public Data File PDF 97-9, 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: legacy data compilation

    DGGS Staff and others, 1997 (source 19 of 24)
    Staff, DGGS, Dighem, and WGM, Inc., 1997, Total field magnetics and detailed electromagnetic anomalies of the northeast Petersville mining district, Alaska: Public Data File PDF 97-13B, 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, 1997 (source 20 of 24)
    Staff, DGGS, Dighem, and WGM, Inc., 1997, Total field magnetics and detailed electromagnetic anomalies of the southeast Petersville mining district, Alaska: Public Data File PDF 97-13C, 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, 1997 (source 21 of 24)
    Staff, DGGS, Dighem, and WGM, Inc., 1997, Total field magnetics and detailed electromagnetic anomalies of the southwest Petersville mining district, Alaska: Public Data File PDF 97-13A, 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, 1997 (source 22 of 24)
    Staff, DGGS, Dighem, and WGM, Inc., 1997, Total field magnetics and electromagnetic anomalies of the Petersville mining district, Alaska: Report of Investigation RI 97-5, 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: legacy data compilation

    DGGS Staff and others, 1997 (source 23 of 24)
    Staff, DGGS, Dighem, and WGM, Inc., 1997, Total field magnetics of the Petersville mining district, Alaska: Report of Investigation RI 97-6, 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: legacy data compilation

    Pritchard, R.A. and Dighem, 1997 (source 24 of 24)
    Pritchard, R.A., and Dighem, 1997, Project report of the airborne geophysical survey for the Chulitna and Petersville mining districts: Public Data File PDF 97-8, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 293 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: 1996 (process 1 of 11)
    Geophysical data - Geophysical data - The airborne geophysical data was acquired with a DIGHEM-V Electromagnetic (EM) system and a Scintrex cesium magnetometer towed at nominal survey altitudes of 30 meters (~100 ft) and 20 meters (~65 ft) respectively. The survey also recorded data from a radar altimeter, GPS navigation system, 50/60 Hz monitors and video camera. Flights were performed with an AS350B-1 Squirrel helicopter at a mean terrain clearance of 200 feet and an average airspeed for the Petersville survey of 68 mph (109 km/h). The flight direction was E-W for the Petersville survey. All survey flight lines were spaced at one-quarter mile. Tie lines were flown perpendicular to the flight lines at intervals of approximately 3 miles. A Sercel NR106 NAVSTAR (RT-DGPS) Global Positioning System was used for both navigation and flight path recovery. The helicopter position was derived every 0.5 seconds using post-flight differential positioning to a relative accuracy of better than 5 m. (Maps produced during 2004 incorrectly state 10 m, and is considered to be a minor error.) Flight path positions were projected onto the Clarke 1866 (UTM zone 5) spheroid, 1927 North American datum using a central meridian (CM) of 153 degrees, a north constant of 0 and an east constant of 500,000. Positional accuracy of the presented data is better than 10 m with respect to the UTM grid.

    Date: 1996 (process 2 of 11)
    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 gradient, 1985, updated to October, 1996) was removed from the leveled magnetic data for the Petersville survey. The aeromagnetic data were interpolated onto a regular 100 m grid using a modified Akima (1970) technique. The magnetic base station was a GSM-19T digital recording proton precession machine with a sensitivity of 0.20 nT and was sampled once every 3 seconds.

    Data sources used in this process:

    • Akima, H., 1970

    Date: 1996 (process 3 of 11)
    Inphase and quadrature components - The DIGHEM-V EM system measured inphase and quadrature components at five frequencies. Two vertical coaxial-coil pairs operated at 898 (900) and 6491 (5,500) Hz while three horizontal coplanar-coil pairs operated at 1049 for flights 30-58 and 1010 for flights 60-67 (900), 7216 (7200), and 56,598 (56 000) Hz. 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 resistivity data were then interpolated onto a regular 100 m grid using a modified Akima (1970) technique. The resulting grids are subjected to a 3x3 hanning filter before contouring and map production. 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.

    Date: 2004 (process 4 of 11)
    Geographically registered gridded data - The binary databases originally created for the 1994 project have been taken from the Fugro Airborne Surveys Archive and converted to Geosoft ASCII format. All data channels are now represented in real world units without the presence of multipliers. No reprocessing of data has been carried out. The data are presented in a modern, updated format. Gridded data of the total magnetic field, and 900 Hz and 7200 Hz coplanar resistivities were converted from 100 m cells as originally provided to 25 m cells and are provided in ER Mapper and Geosoft binary grid formats. Various vector files were either remade or converted from other formats to Autocad dxf format, version 13. The data contour vector files were recreated for the new grids. The original files containing the flight lines, interpretation overlays (associated with DGGS Public-data File 97-8), and the electromagnetic anomaly symbols [included on DGGS PDF 97-13A, PDF 97-13B, and PDF 97-13C] were converted to the Autocad format as part of this project.

    Date: 2005 (process 5 of 11)
    Print files - Plot files of the maps were produced by Fugro in HPGL2, postscript, and Adobe Acrobat formats. The HPGL2 files were produced by Hewlett Packard DesignJet 5500 HPGL/2 driver version 5.32 and will not work with all plotters, but do plot on the DGGS HP DesignJet 5000. The postscript files were produced by Hewlett Packard DesignJet 5000 Postscript 3 V4.28 and should work with all HP plotters that can read Postscript 3. The HPGL2 files have brighter colors and sharper topography than the postscript files.

    Date: 2015 (process 6 of 11)
    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., 1997
    • Burns, L.E. and others, 2005, 0 p.
    • Burns, L.E. and others, 2005, 0 p.
    • Burns, L.E. and others, 2005, 0 p.
    • Burns, L.E. and others, 2005, 0 p.
    • Burns, L.E. and others, 2005
    • Burns, L.E. and others, 2005, 0 p.
    • Burns, L.E. and others, 2005, 0 p.
    • DGGS Staff and others, 1997
    • DGGS Staff and others, 1997
    • DGGS Staff and others, 1997
    • DGGS Staff and others, 1997
    • DGGS Staff and others, 1997
    • DGGS Staff and others, 1997
    • DGGS Staff and others, 1997
    • DGGS Staff and others, 1997
    • DGGS Staff and others, 1997
    • DGGS Staff and others, 1997
    • DGGS Staff and others, 1997
    • DGGS Staff and others, 1997
    • DGGS Staff and others, 1997
    • Pritchard, R.A. and Dighem, 1997

    Date: 2015 (process 7 of 11)
    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 8 of 11)
    Geographically registered gridded data in Geosoft GRD format - Geographically registered gridded data in Geosft GRD format - These data were created by DGGS using the final ascii data. Geosft Oasis montaj v8.2 was used to create the grid files. 80 meter grid cell size and the minimum curvature operate were used in the production of these grids. The analytic signal and first vertical derivative grids are smoothed using a 9x9 convolution filter.

    Date: 2015 (process 9 of 11)
    Geographically registered gridded data in GeoTiff format - These data were created by DGGS using Geosft Oasis montaj v8.2. Geosoft grd files were displayed in Geosft and exported to GeoTiff. A matching colorbar for each grid was displayed in Geosoft and export as a GeoTiff.

    Date: 2015 (process 10 of 11)
    Google Earth KMZ files - Created Google Earth KMZ files from the GeoTiff format gridded data using ESRI ArcMap 10.2.2.

    Date: 2015 (process 11 of 11)
    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 ESRI shapefile.

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

    Pinney, D.S., Szumigala, D.J., Mayer, J.L., Liss, S.A., Clautice, K.H., McCarthy, A.M., LePain, D.L., Combellick, R.A., and Strandberg, N.M., 1998, Geochemical trace-element data from rocks collected in the Petersville (Yentna) mining district, 1998: Public Data File PDF 98-32A, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 19 p., 1 sheet, scale 1:63,360
    Pinney, D.S., Szumigala, D.J., Mayer, J.L., Liss, S.A., and Clautice, K.H., 1998, Geochemical major-oxide and trace-element data from rocks collected in the Petersville (Yentna) mining district, 1998: Public Data File PDF 98-32B, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 6 p., 1 sheet, scale 1:63,360
    Reger, R.D., Combellick, R.A., and Pinney, D.S., 1999, Reconnaissance map of glacial limits in the Petersville (Yentna) mining district, Alaska: Report of Investigation RI 99-7, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:63,360
    Reger, R.D., Combellick, R.A., and Pinney, D.S., 1999, Reconnaissance surficial-geologic map of the Petersville (Yentna) mining district, Alaska: Report of Investigation RI 99-9, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:63,360
    Szumigala, D.J., Pinney, D.S., LePain, D.L., Liss, S.A., Burns, L.E., Clautice, K.H., Mayer, J.L., and McCarthy, A.M., 2000, Interpretive bedrock-geologic map of the Petersville (Yentna) mining district, Alaska: Report of Investigation RI 2000-3, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:63,360


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

  1. How well have the observations been checked?

    Geophysical data were acquired during an airborne survey. The magnetometer used had a sensitivity of 0.01 nT. Resistivity sensitivity varies among the different frequencies from 0.06 ppm to 0.30 ppm.

  2. How accurate are the geographic locations?

    The helicopter position was derived every 0.5 seconds using post-flight differential positioning to a relative accuracy of better than 5 m. Positional accuracy of the presented data is better than 10 m with respect to the UTM grid. Further inaccuracies may be introduced by the interpolation and gridding process.

  3. How accurate are the heights or depths?

    Manufacturer's accuracy on the radar altimeter used during data acquisition is 3.0 meters. The accuracy of the elevation calculation used for the digital terrain model is directly dependent on the accuracy of the two input parameters, ALTR and HMSL. The ALTR value may be erroneous in areas of heavy tree cover, where the altimeter reflects the distance to the tree canopy rather than the ground. The HMSL value is primarily dependent on the number of available satellites. Although post-processing of GPS data will yield X and Y accuracies in the order of 5 meters, the accuracy of the Z value is usually much less, sometimes in the +/-20 meter range.

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

    This dataset includes files that contain processed aeromagnetic measurements, electromagnetic measurements, altimetry measurements, and locational data for the Petersville 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.


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 2015-3

  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: 22-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 Mon Jun 22 09:23:14 2015