East Styx survey area: Airborne magnetic, electromagnetic and radiometric data in line (point), grid, vector, and map formats, Talkeetna, Tyonek, McGrath, and Lime Hills quadrangles, south-central Alaska

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Frequently anticipated questions:

What does this data set describe?

Title:
East Styx survey area: Airborne magnetic, electromagnetic and radiometric data in line (point), grid, vector, and map formats, Talkeetna, Tyonek, McGrath, and Lime Hills quadrangles, south-central Alaska
Abstract:
This digital publication, GPR 2014-5, contains data produced from airborne geophysical surveys conducted in 2012 and 2013 for the East Styx survey area in the McGrath and Yentna mining districts, Talkeetna, Tyonek, McGrath, and Lime Hills quadrangles, south-central Alaska. Aeromagnetic, electromagnetic (EM), and radiometric data were acquired by helicopter for about 1060 sq miles. CGG's frequency-domain DIGHEM V system was used for the EM data. GPR 2014-5 includes (1) raw and processed linedata; (2) gridded, Google Earth, and Geotiff formats of the calculated linedata; (3) maps of the data and flight lines; and (4) vector files of data contours and flight lines.
Supplemental_Information:
The airborne data were acquired and processed under contract between the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), and Fugro GeoServices, Inc. CGG, the subcontractor, acquired and processed the data in 2013 and 2014. This publication will be appended in the future to include the technical project report, interpretation map, and EM anomalies, as well as other files.
This metadata file lists file names and definitions in the 'Entity_and_Attribute_Information' section. This information is also provided in the file 'gpr2014-005_readme', included in .txt and PDF formats. Besides file names and definitions, the readme file contains map numbers and grid correlations, projection information, and much general information. Some detailed information about the data is given in the 'Entity_and_Attribute_Information' section of this metadata file. 'EStyx_linedata.txt' gives information on the linedata in an easy-to-read format. All data are provided in NAD27, UTM zone 5N, except for Google Earth KMZ files, which are in Geographic Coordinate System (Simple Cylindrical projection) with a WGS84 datum. Besides NAD27, UTM zone 5N easting and northing coordinates, the linedata files also include latitude and longitude (Geographic Coordinate System with a WGS84 datum).
  1. How should this data set be cited?

    Burns, L.E., CGG, and Fugro GeoServices, Inc., 2014, East Styx survey area: Airborne magnetic, electromagnetic and radiometric data in line (point), grid, vector, and map formats, Talkeetna, Tyonek, McGrath, and Lime Hills quadrangles, south-central Alaska: Geophysical Report GPR 2014-5, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), Fairbanks, AK, USA.

    Online Links:

    Other_Citation_Details: 1 DVD, scale 1:63,360.

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -153.11
    East_Bounding_Coordinate: -151.73
    North_Bounding_Coordinate: 62.30
    South_Bounding_Coordinate: 61.64

  3. What does it look like?

    gpr2014-5_browsegraphic.pdf (PDF)
    The browse graphic file contains three location maps showing 1) East Styx survey area and adjacent published surveys within Alaska 2) a view of the survey area and adjacent published surveys in the McGrath, Talkeetna, Tyonek, and Lime Hills quardangles, and 3) location of map sheets in the survey area. Four images of the East Styx survey data are included as figures 4) the residual magnetic field (RMI), 5) first vertical derivative of the RMI, and 6) analytic signal of the magnetic data, and 7) 7200 Hz coplanar apparent resistivity.

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

    Beginning_Date: Jul-2013
    Ending_Date: Nov-2014
    Currentness_Reference: publication date

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form:
    raster digital data, tabular digital data, and vector 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: 0.9996
      Longitude_of_Central_Meridian: -153
      Latitude_of_Projection_Origin: 0
      False_Easting: 500000
      False_Northing: 0

      Planar coordinates are encoded using row and column
      Abscissae (x-coordinates) are specified to the nearest 25
      Ordinates (y-coordinates) are specified to the nearest 25
      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 1/294.978698.

  7. How does the data set describe geographic features?

    EStyx_EM.GDB, EStyx_EM_part1.XYZ, EStyx_EM_part2.XYZ, and EStyx_EM_part3.XYZ
    The file 'EStyx_EM' contains raw and processed linedata and related calculated fields for locational, magnetic, and electromagnetic data. The file is provided in Geosoft binary grid (GDB) and Geosoft ASCII (XYZ) formats; formatting varies slightly between these two formats. Except for the 'LINE' attribute, all attributes, including 'DATE' and 'FLIGHT', are represented by one of the 50 data columns on each record. The 'LINE' and 'FLIGHT' attributes are discussed further in the attribute 'ID Cell'. (Source: L.E. Burns & Fugro Airborne Surveys)

    ID_CELL
    The 'ID CELL' occurs in the GDB file only; the contents of the 'ID CELL' are also present in the XYZ file. In the 'ID CELL' for this project, the 'LINE' attribute is followed by a colon followed by the 'FLIGHT' attribute (e.g., 'L10010:24145' and 'T19420:24176'). More than one line is typically flown on a particular date and flight; more than one flight may be flown on a particular date. Each ID-cell value will have an associated spreadsheet view consisting of a column for each of the 50 attributes. In the XYZ file, the 'LINE' and 'FLIGHT' attributes and the 'DATE' are present as header lines, one attribute per line, before each set of associated data, for example: 
      //Flight 24145
  //Date 7/28/2013
  Line 10010 (or Tie instead of Line when appropriate)
  Followed by all records for points sampled along Line 10010.
     (Pattern is repeated for each line number).
    The 'ID CELL' content, particularly combined with the definitions below for this particular survey, provides information about the flight line layout. (Source: L.E. Burns & Fugro Airborne Surveys)

    Definitions of the 'LINE' and 'FLIGHT' attributes are listed below. 

     LINE TYPES and SYMBOLS:
 Traverse lines - flown at a heading of 70 degrees (NE-SW)
 Tie lines      - flown at a heading of 340 degrees (NW-SE)
 Border lines   - present inside and parallel to the survey
                  tract border where traverse or tie lines
                  are not parallel to the border
 Traverse lines - 'L' (GDB file); 'LINE' (XYZ file)
 Tie and border lines - 'T' (GDB file); 'TIE' (XYZ file)
------------------------------------------------------------
 LINE NUMBERS
 Planned flight lines increase by 10 in a consistent fashion. For this project, traverse line numbers increase from north to south; tie line numbers increase from southwest to northeast; and border line numbers increase in a clockwise direction.

 When more than one uninterrupted flight traverse was needed to complete a planned flight line, the fifth digit of the line number is increased by '1' for each new flight segment/version.
------------------------------------------------------------
 'FLIGHT' DESIGNATORS
 Four different HeliDAS (data acquisition systems) units were used, and are designated '4', '20', '24', and '29'. The first digit ('4') of the 4 digit flight designators and the first two numbers ('20', '24', and '29') of the 5 digits flight designators identify the HeliDAS (data acquisition system). The remaining three digits are the flight identification number, e.g., '018'.

    x_NAD27z5N
    easting NAD 27 (UTM Zone 5N) (Source: CGG)

    Range of values
    Minimum:494544.38
    Maximum:567436.25
    Units:m

    y_NAD27z5N
    northing NAD 27 (UTM Zone 5N) (Source: CGG)

    Range of values
    Minimum:6834604.35
    Maximum:6907054.77
    Units:m

    fid
    Fiducial increment; the time in tenths of seconds from the start to the end of the particular flight. Sampling typically occurred at each fiducial for almost all items in the database. (Source: CGG)

    The attribute measurement resolution is 0.1 second. The values increase from the beginning of a flight to the end. Only FIDs during production flights are included in the database.

    lat_WGS84
    latitude WGS 84 (Source: CGG)

    Range of values
    Minimum:61.6443020
    Maximum:62.2962165
    Units:degrees

    lon_WGS84
    longitude WGS 84 (Source: CGG)

    Range of values
    Minimum:-153.1055790
    Maximum:-151.7278196
    Units:degrees

    flight
    The first digit of the 4 digit flight numbers and the first 2 digits of the 5 digit flight numbers are CGGs identification number for the HeliDAS (data acquisition) systems for this survey, i.e., '4', '20', '24', and '29'. The last three digits represent the flight numbers associated with this project. A flight number is the number of the helicopter flight from home base to home base associated with this project. The flights are numbered from the beginning of the project to the end. Only those flight numbers containing acquisition of final data measurements are included in the database. Four different flying periods and helicopters were used during data acquisition. Four ranges of flight numbers are given below, and correspond, in order, to the four sets of dates in the 'DATE' attributes immediately following. (Source: CGG)

    Range of values
    Minimum:4035
    Maximum:4188
    Units:flight

    Range of values
    Minimum:20030
    Maximum:20030
    Units:flight

    Range of values
    Minimum:24095
    Maximum:24249
    Units:flight

    Range of values
    Minimum:29024
    Maximum:29029
    Units:flight

    date
    flight date (yyyy/mm/dd) (Source: CGG)

    The dates for the four periods of flying by four different helicopters are shown below.

    altrad_calcbird
    calculated bird height above surface to simulate location of radar altimeter in the bird; radar altimeter measurement was recorded in helicopter. Altrad_calcbird was calculated by subtracting a constant representing the distance in altitude from helicopter to the bird when towing and recording data. (Source: CGG)

    Range of values
    Minimum:15.47
    Maximum:750.43
    Units:m

    altlas_bird
    bird height above surface, measured by laser altimeter in the EM bird (Source: CGG)

    Range of values
    Minimum:5.16
    Maximum:831.11
    Units:m

    gpsz
    bird height above spheroid. The GPSZ (or GPS-Z) value is primarily dependent on the number of available satellites. Although post-processing of GPS data will yield X and Y accuracies on the order of 1 meter, the accuracy of the Z value is usually much less, sometimes in the +/-20 meter range. (Source: CGG)

    Range of values
    Minimum:197.89
    Maximum:2822.20
    Units:m

    dtm
    Digital terrain/elevation model (NAD27 UTM Zone 5N); data in m. Elevation calculation used for the digital elevation model is directly dependent on the accuracy of the two input parameters, ALTLAS_BIRD and GPSZ. The ALTBIRD value may be unreliable in areas of heavy tree cover, where the altimeter reflects the distance to the tree canopy rather than the ground. Although post-processing of GPS data will yield X and Y accuracies on the order of 1 meter, the accuracy of the Z value (GPSZ) is usually much less, sometimes in the +/-20 meter range. (Source: CGG)

    Range of values
    Minimum:156.92
    Maximum:2740.95
    Units:m

    diurnal_filt
    measured diurnal ground magnetic intensity; interpolated to 0.1 sec. from 1.0 second measurements (Source: CGG)

    Range of values
    Minimum:55293.24
    Maximum:55893.51
    Units:nT

    diurnal_cor
    diurnal correction - base removed; calculated from interpolated diurnal_filt (Source: CGG)

    Range of values
    Minimum:-446.76
    Maximum:256.52
    Units:nT

    mag_raw
    total magnetic field - spike rejected (Source: CGG)

    Range of values
    Minimum:52839.14
    Maximum:58148.10
    Units:nT

    mag_lag
    total magnetic field - corrected for lag (Source: CGG)

    Range of values
    Minimum:52839.14
    Maximum:58148.10
    Units:nT

    mag_diu
    total magnetic field - diurnal variation removed (Source: CGG)

    Range of values
    Minimum:52863.15
    Maximum:58158.03
    Units:nT

    igrf
    international geomagnetic reference field (Source: CGG)

    Range of values
    Minimum:55638.18
    Maximum:55917.42
    Units:nT

    mag_rmi
    residual magnetic intensity - IGRF removed, then leveled - final (Source: CGG)

    Range of values
    Minimum:-2926.47
    Maximum:2365.32
    Units:nT

    magigrf
    total magnetic field with IGRF removed - mag_rmi with constant added back - final (Source: CGG)

    Range of values
    Minimum:52743.42
    Maximum:58035.21
    Units:nT

    cpi900_FILT
    coplanar inphase 900 Hz - unlevelled (Source: CGG)

    Range of values
    Minimum:-155.46
    Maximum:1505.18
    Units:ppm

    cpq900_FILT
    coplanar quadrature 900 Hz - unlevelled (Source: CGG)

    Range of values
    Minimum:-218.92
    Maximum:928.55
    Units:ppm

    cxi1000_FILT
    coaxial inphase 1000 Hz - unlevelled (Source: CGG)

    Range of values
    Minimum:-35.85
    Maximum:465.82
    Units:ppm

    cxq1000_FILT
    coaxial quadrature 1000 Hz - unlevelled (Source: CGG)

    Range of values
    Minimum:-16.13
    Maximum:241.82
    Units:ppm

    cxi5500_FILT
    coaxial inphase 5500 Hz - unlevelled (Source: CGG)

    Range of values
    Minimum:-2433.96
    Maximum:678.64
    Units:ppm

    cxq5500_FILT
    coaxial quadrature 5500 Hz - unlevelled (Source: CGG)

    Range of values
    Minimum:-18.17
    Maximum:505.14
    Units:ppm

    cpi7200_FILT
    coplanar inphase 7200 Hz - unlevelled (Source: CGG)

    Range of values
    Minimum:-103.26
    Maximum:2094.79
    Units:ppm

    cpq7200_FILT
    coplanar quadrature 7200 Hz - unlevelled (Source: CGG)

    Range of values
    Minimum:-14.73
    Maximum:1232.78
    Units:ppm

    cpi56K_FILT
    coplanar inphase 56 kHz - unlevelled (Source: CGG)

    Range of values
    Minimum:-91.49
    Maximum:2258.66
    Units:ppm

    cpq56K_FILT
    coplanar quadrature 56 kHz - unlevelled (Source: CGG)

    Range of values
    Minimum:-48.66
    Maximum:1434.32
    Units:ppm

    cpi900
    coplanar inphase 900 Hz (Source: CGG)

    Range of values
    Minimum:-149.65
    Maximum:1505.37
    Units:ppm

    cpq900
    coplanar quadrature 900 Hz (Source: CGG)

    Range of values
    Minimum:-1.53
    Maximum:928.85
    Units:ppm

    cxi1000
    coaxial inphase 1000 Hz (Source: CGG)

    Range of values
    Minimum:-35.93
    Maximum:462.19
    Units:ppm

    cxq1000
    coaxial quadrature 1000 Hz (Source: CGG)

    Range of values
    Minimum:-15.99
    Maximum:242.38
    Units:ppm

    cxi5500
    coaxial inphase 5500 Hz (Source: CGG)

    Range of values
    Minimum:-32.54
    Maximum:674.45
    Units:ppm

    cxq5500
    coaxial quadrature 5500 Hz (Source: CGG)

    Range of values
    Minimum:-10.45
    Maximum:351.30
    Units:ppm

    cpi7200
    coplanar inphase 7200 Hz (Source: CGG)

    Range of values
    Minimum:-103.25
    Maximum:2092.15
    Units:ppm

    cpq7200
    coplanar quadrature 7200 Hz (Source: CGG)

    Range of values
    Minimum:-4.12
    Maximum:1232.23
    Units:ppm

    cpi56k
    coplanar inphase 56k Hz (Source: CGG)

    Range of values
    Minimum:-91.60
    Maximum:2258.13
    Units:ppm

    cpq56K
    coplanar quadrature 56k Hz (Source: CGG)

    Range of values
    Minimum:-6.99
    Maximum:1433.56
    Units:ppm

    res900
    apparent resistivity 900 Hz; cut-off value for apparent resistivity was 1325; more information in process steps (Source: CGG)

    Range of values
    Minimum:0.37
    Maximum:1325
    Units:ohm-;m

    res7200
    apparent resistivity 7200 Hz; cut-off value for apparent resistivity was 10750; more information in process steps (Source: CGG)

    Range of values
    Minimum:1.43
    Maximum:10750
    Units:ohm-m

    res56K
    apparent resistivity 56k Hz; cut-off value for apparent resistivity was 60000; more information in process steps (Source: CGG)

    Range of values
    Minimum:1.75
    Maximum:60000
    Units:ohm-m

    dep900
    apparent depth 900 Hz; more information in process steps (Source: CGG)

    Range of values
    Minimum:-110.45
    Maximum:294.61
    Units:m

    dep7200
    apparent depth 7200 Hz; more information in process steps (Source: CGG)

    Range of values
    Minimum:-110.93
    Maximum:153.85
    Units:m

    dep56K
    apparent depth 56k Hz; more information in process steps (Source: CGG)

    Range of values
    Minimum:-128.91
    Maximum:160.49
    Units:m

    difi
    difference channel based on cxi5500 & cpi7200 (Source: CGG)

    Range of values
    Minimum:-139.77
    Maximum:301.56
    Units:unitless

    difq
    difference channel based on cxq5500 & cpq7200 (Source: CGG)

    Range of values
    Minimum:-33.26
    Maximum:131.72
    Units:unitless

    cppl
    coplanar powerline monitor (Source: CGG)

    Range of values
    Minimum:0.00
    Maximum:0.00
    Units:unitless

    cxsp
    coaxial spherics monitor (Source: CGG)

    Range of values
    Minimum:0.00
    Maximum:0.00
    Units:unitless

    cpsp
    coplanar spherics monitor (Source: CGG)

    Range of values
    Minimum:0.00
    Maximum:0.00
    Units:unitless

    EStyx_RAD.GDB, EStyx_RAD_part1.XYZ, EStyx_RAD_part2.XYZ, and EStyx_RAD_part3.XYZ,
    The file 'EStyx_RAD' contains raw and processed linedata and related calculated fields for locational and radiometric data. The linedata file is provided in Geosoft binary grid (GRD) and Geosoft ASCII (XYZ) formats; formatting varies slightly between these two formats. Except for the 'LINE' attribute, all attributes, including 'DATE' and 'FLIGHT', are represented by one of the 31 data columns on each record. The 'LINE' and 'FLIGHT' attributes are discussed further in the attribute 'ID Cell'. (Source: L.E. Burns & CGG)

    ID_CELL
    The 'ID CELL' definition and the items mentioned under "Unrepresentable_Domain" for the RAD database is the same as given above for those items in MAG and EM LINEDATA. (Source: L.E. Burns & CGG)

    Described above in MAG and EM LINEDATA

    X_NAD27z5N
    easting NAD27 (UTM Zone 5N) (Source: CGG)

    Range of values
    Minimum:494544.38
    Maximum:567436.25
    Units:m

    Y_NAD27z5N
    northing NAD27 (UTM Zone 5N) (Source: CGG)

    Range of values
    Minimum:6834604.35
    Maximum:6907054.77
    Units:m

    FID
    Fiducial increment; the time in tenths of seconds from the start to the end of the particular flight. Sampling typically occurred at each fiducial for almost all items in the database. (Source: CGG)

    The attribute measurement resolution is 0.1 second. The values increase from the beginning of a flight to the end. Only FIDs during production flights are included in the database.

    LAT_WGS84
    latitude WGS84 (Source: CGG)

    Range of values
    Minimum:61.6443020
    Maximum:62.2962165
    Units:degrees

    LON_WGS84
    longitude WGS84 (Source: CGG)

    Range of values
    Minimum:-153.1055790
    Maximum:-151.7278196
    Units:degrees

    FLIGHT
    The first digit of the 4 digit flight numbers and the first 2 digits of the 5 digit flight numbers are CGGs identification number for the HeliDAS (data acquisition) systems for this survey, i.e., '4', '20', '24', and '29'. The last three digits represent the flight numbers associated with this project. A flight number is the number of the helicopter flight from home base to home base associated with this project. The flights are numbered from the beginning of the project to the end. Only those flight numbers containing acquisition of final data measurements are included in the database. Four different flying periods and helicopters were used during data acquisition. Four ranges of flight numbers are given below, and correspond, in order, to the four sets of dates in the 'DATE' attributes immediately following. (Source: CGG)

    Range of values
    Minimum:20030
    Maximum:20030
    Units:flight

    Range of values
    Minimum:4035
    Maximum:4188
    Units:flight

    Range of values
    Minimum:24095
    Maximum:24249
    Units:flight

    Range of values
    Minimum:29024
    Maximum:29029
    Units:flight

    date
    flight date (yyyy/mm/dd) (Source: CGG)

    The data acquisition minimum and maximum dates for the four different HeliDas systems are shown below and correspond in order with the flight numbers in the previous attribute.

    ALTRAD_HELI
    helicopter height above surface from radar altimeter (Source: CGG)

    Range of values
    Minimum:40.47
    Maximum:775.43
    Units:m

    DTM
    Digital terrain/elevation model (NAD27 UTM Zone 5N); data in m. Elevation calculation used for the digital elevation model is directly dependent on the accuracy of the two input parameters, ALTLAS_BIRD and GPSZ. The ALTBIRD value may be unreliable in areas of heavy tree cover, where the altimeter reflects the distance to the tree canopy rather than the ground. Although post-processing of GPS data will yield X and Y accuracies on the order of 1 meter, the accuracy of the Z value (GPSZ) is usually much less, sometimes in the +/-20 meter range. (Source: CGG)

    Range of values
    Minimum:156.92
    Maximum:2740.95
    Units:m

    TC_RAW
    raw total counts (Source: CGG)

    Range of values
    Minimum:142
    Maximum:4500
    Units:counts

    Th_RAW
    raw thorium counts (Source: CGG)

    Range of values
    Minimum:0
    Maximum:132
    Units:counts

    U_RAW
    raw uranium counts (Source: CGG)

    Range of values
    Minimum:0
    Maximum:167
    Units:counts

    K_RAW
    raw potassium counts (Source: CGG)

    Range of values
    Minimum:5
    Maximum:408
    Units:counts

    U_UP
    raw upward looking uranium (Source: CGG)

    Range of values
    Minimum:0
    Maximum:28
    Units:counts

    Cosmic
    cosmic counts (Source: CGG)

    Range of values
    Minimum:40
    Maximum:279
    Units:cps (counts per second)

    EffectiveHeight
    effective height at STP (standard temperature and pressure) (Source: CGG)

    Range of values
    Minimum:23.78
    Maximum:2082.18
    Units:m

    LIVETIME
    live time (Source: CGG)

    Range of values
    Minimum:858
    Maximum:999
    Units:ms (millisecond)

    KPA
    barometric pressure (Source: CGG)

    Range of values
    Minimum:70.95
    Maximum:101.08
    Units:kPa (kilopascal)

    TEMP_EXT
    external temperature in Celsius (Source: CGG)

    Range of values
    Minimum:-9.5
    Maximum:25.1
    Units:C

    TC
    corrected total counts (Source: CGG)

    Range of values
    Minimum:-21.99
    Maximum:8045.06
    Units:cps (counts per second)

    Th
    corrected thorium counts (Source: CGG)

    Range of values
    Minimum:-9.17
    Maximum:292.05
    Units:cps (counts per second)

    U
    corrected uranium counts (Source: CGG)

    Range of values
    Minimum:-27.82
    Maximum:202.25
    Units:cps (counts per second)

    K
    corrected potassium counts (Source: CGG)

    Range of values
    Minimum:-38.05
    Maximum:1317.28
    Units:cps (counts per second)

    eU
    uranium concentration (Source: CGG)

    Range of values
    Minimum:-4.29
    Maximum:31.21
    Units:ppm

    eTh
    thorium concentration (Source: CGG)

    Range of values
    Minimum:-2.43
    Maximum:77.26
    Units:ppm

    percentK
    potassium concentration (Source: CGG)

    Range of values
    Minimum:-0.65
    Maximum:22.63
    Units:%

    ratio_eU_percentK
    uranium/potassium concentration ratio (Source: CGG)

    Range of values
    Minimum:0.16
    Maximum:17.99
    Units:ppm/%

    ratio_eTh_percentK
    thorium/potassium concentration ratio (Source: CGG)

    Range of values
    Minimum:0.27
    Maximum:21.70
    Units:ppm/%

    ratio_eU_eTh
    uranium/thorium concentration ratio (Source: CGG)

    Range of values
    Minimum:0.03
    Maximum:8.44
    Units:unitless

    nadr
    natural air absorbed dose rate (Source: CGG)

    Range of values
    Minimum:-1.12
    Maximum:410.46
    Units:nGy/h (nanogray/hour)

    Spec256_DOWN
    radiometric spectrum; present in the GDB file, but not the XYZ file. (Source: CGG)

    The radiometric spectrum for each sample point is in the form of an array.

    gpr2014-5_GRIDSasGRD_NAD27_z5N.zip, gpr2014-5GRIDSasERS_NAD27_z5N.zip, gpr2014-5_GEOTIFFS_NAD27_z5N.zip, and gpr2014-5_KMZS_WGS84.zip,
    Because definitions of the data included in the grids, Geotiffs and KMZs are the same, they are discussed together. The zip files mentioned above contain the 21 grids, 21 Geotiffs, and 21 Google Earth KMZ files appropriate supporting files for the East Styx survey. Both Geosoft binary float (GRD) and ER Mapper (ERS) formats are provided. All grids are in NAD27 datum, UTM Zone 5N. The grids have been resampled to 25 m cell size. Grids can be viewed using downloadable free grid-viewing software from Geosoft or ER Mapper. More information is provided in the 'Technical Prerequisites' section of this metadata file. The Geosoft grid is contained in one file (GRD), but the ER Mapper grid consists of two files, a header file (.ERS) and a data file (no extension). Both ER Mapper files are necessary to view a grid or to convert it to another software format. Projection files (.GRD.GI and .ERS.GRD.GI) produced from Geosoft Oasis Montaj are provided for each Geosoft and ER Mapper grid file respectively. Placing these files in the same directory as the grids allows Oasis Montaj and ER Mapper to locate the grids geographically without manually assigning the projection. A data image was made from each of the different 21 grid files and each data image is provided with corresponding color bar in the Geotiffs and KMZ files. While three sheets are needed to see the image for each type of map, the images shown in the Geotiff or KMZ files show the entire survey area. The Geotiffs and the Google Earth KMZs will automatically open in the correct projection in a GIS program or Google Earth respectively. The apparent resistivity grids and images are the most affected with missing values. Rugged terrane caused flying to be too high for accurate resolution of the apparent resistivity data. Resampling from 80 m to 25 m exacerbated the size of some of the blank areas. (Source: CGG)

    ESt_MagRMI
    Final residual magnetic field (nT) with IGRF removed; produced by resampling of the grid with 80 m cell size to grid with 25 m cell size. An image is shown in map numbers GPR2014-5-1 and 2, a Geotiff, and a KMZ. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_MagIGRF
    Final total magnetic field (nT) - final, with IGRF removed; produced by resampling of the grid with 80 m cell size to grid with 25 m cell size. An image of this grid provided as a Geotiff and a KMZ. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_1VD
    Final first vertical derivative 'dz' (nT/m) of the total magnetic field with IGRF removed; also referred to as 'calculated vertical gradient' (cvg). This grid was produced by resampling of the grid with 80 m cell size to grid with 25 m cell size. An image of this grid is shown in map number GPR2014-5-3, a Geotiff, and a KMZ. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_ASig
    Final analytic signal (nT/m); produced by resampling the grid with 80 m cell size to grid with 25 m cell size. An image of this grid is shown in map numbers GPR2014-5-4 and 5, a Geotiff, and a KMZ. A color shadow image of this grid is shown in map number GPR2014-7. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_TiltDer
    Final tilt derivative (degrees) of the total magnetic field with IGRF removed; produced by resampling the grid with 80 m cell size to grid with 25 m cell size. An image of this grid is shown in map GPR2014-5-6, a Geotiff, and a KMZ. Contours produced from the 25 m tilt derivative grid are also shown upon a color shadow residual magnetic field image (ESt_MagRMI) in map GPR2014-5-7. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_Res56k
    Final 56,000 (56k) Hz. apparent coplanar resistivity (ohm-m); produced by resampling the grid with 80 m cell size to grid with 25 m cell size. An image of this grid is shown in map numbers GPR2014-5-8 and 9, a Geotiff, and a KMZ. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_Res7200
    Final 7200 Hz. apparent coplanar resistivity (ohm-m); produced by resampling grid with 80 m cell size to grid with 25 m cell size. An image from the grid is shown in map numbers GPR2014-5-10 and 11, a Geotiff, and a KMZ. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_Res900
    Final 900 Hz. apparent coplanar resistivity (ohm-m); produced by resampling grid with 80 m cell size to grid with 25 m cell size. An image of this grid is shown in map numbers GPR2014-5-12 and 13, a Geotiff and a KMZ. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_DTM
    Final digital terrain or elevation model (m); produced by resampling grid with 80 m cell size to grid with 25 m cell size. An image of this grid is shown as a Geotiff and a KMZ. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_AltLasBird
    Final EM bird height (m) above surface; produced by resampling grid with 80 m cell size to grid with 25 m cell size. An image of the final grid is shown as a Geotiff and a KMZ. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_K_cc
    Final corrected thorium counts (cps); produced by resampling grid with 100 m cell size to grid with 25 m cell size; an image shown in a Geotiff and a KMZ. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_Th_cc
    Final corrected thorium counts (cps); produced by resampling grid with 100 m cell size to grid with 25 m cell size; an image shown in a Geotiff and a KMZ. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_U_cc
    Final corrected uranium counts (cps); produced by resampling grid with 100 m cell size to grid with 25 m cell size; an image shown in a Geotiff and a KMZ. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_TC_cc
    Final corrected total counts (cps); produced by resampling grid with 100 m cell size to grid with 25 m cell size. An image of this grid is shown in a Geotiff and a KMZ. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_ratio_eTh_percentK
    Final for equivalent thorium/percent potassium ratio (ppm/%); produced by resampling grid with 100 m cell size to grid with 25 m cell size. An image of this grid is shown in maps GPR2014-5-14 and 15, a Geotiff, and a KMZ. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_ratio_eU_percentK
    Final equivalent uranium/percent potassium ratio (ppm/%); produced by resampling grid with 100 m cell size to grid with 25 m cell size. An image of this grid is shown in maps GPR2014-5-16 and 17, a Geotiff and a KMZ. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_ratio_eU_eTh
    Final equivalent uranium/equivalent thorium ratio (unitless); produced by resampling grid with 100 m cell size to grid with 25 m cell size. An image of this grid is shown in maps GPR2014-5-18 and 19, a Geotiff, and a KMZ. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_percentK
    Final percent potassium (%); produced by resampling grid with 100 m cell size to grid with 25 m cell size. An image of this grid is shown in maps GPR2014-5-20 and 21, a Geotiff, and a KMZ. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_eTh
    Final equivalent thorium (ppm); produced by resampling grid with 100 m cell size to grid with 25 m cell size. An image of this grid is shown in maps GPR2014-5-22 and 23, a Geotiff, and a KMZ. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_eU
    Final equivalent uranium (ppm); produced by resampling grid with 100 m cell size to grid with 25 m cell size. An image of this grid is shown in maps GPR2014-5-24 and 25, a Geotiff, and a KMZ. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    ESt_nadr
    Final natural air absorbed dose rate [nGy/h (nanogray per hour)]; produced by resampling grid with 100 m cell size to grid with 25 m cell size. An image of this grid is shown in maps GPR2014-5-26 and 27. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    GPR2014-5_VECTORS.zip
    Data contours produced for the maps are provided in Autocad DXF and ESRI shape file format. Except for maps GPR2014-5-6 and GPR2014-5-7, the vector files are shown on the maps without topography. Caution should be used when reading the contour labels from the shape and dxf files as they may appear to be with a different line. Additional vector files included are the flight path, the Alaska Section Grid, and a UTM grid for the map area. 
     Each file format (DXF and shape file) contains the same information. A dxf file (e.g. ESt_magRMI.dxf) contains the information in layers within the file, and the shape file format consists of each layer as a separate file (e.g. ESt_magRMI_1, ESt_magRMI_2, ESt_magRMI_3, and ESt_magRMI_4). Most sets of shape files in this publication consist of the numbers 1-4 or 1-5. Please refer to the map legends for appropriate line widths and particular label placement.
 Neither the DXF nor the shape files are attributed. All labeling is done through individual alphanumeric characters, e.g. line number 3050 would be represented by 4 individual characters instead of one number.
    (Source: CGG)

    ESt_magRMI
    Contours, "triangles" denoting lows, and labels for residual magnetic field data (Source: CGG)

    vector file

    ESt_ASig
    Contours and labels for the analytic signal data (Source: CGG)

    vector file

    ESt_TiltDer
    Contours and labels for the magnetic tilt derivative data (Source: CGG)

    vector file

    ESt_Res56k
    Contours and labels for the 56,000 Hz coplanar apparent resistivity data (Source: CGG)

    vector file

    ESt_Res7200
    Contours and labels for the 7200 Hz coplanar apparent resistivity data (Source: CGG)

    vector file

    ESt_Res900
    Contours and labelsfor the 900 Hz coplanar apparent resistivity data (Source: CGG)

    vector file

    ESt_percentK
    Contours and labels for percent potassium (%) data (Source: CGG)

    vector file

    ESt_eTh
    Contours and labels for equivalent thorium (ppm) data (Source: CGG)

    vector file

    ESt_eU
    Contours and labels for equivalent uranium (ppm) data (Source: CGG)

    vector file

    ESt_ratio_eTh_percentK
    Contours and labels for equivalent thorium/percent potassium ratio (ppm/%) data (Source: CGG)

    vector file

    ESt_ratio_eU_percentK
    Contours and labels for equivalent uranium/percent potassium ratio (ppm/%) data (Source: CGG)

    vector file

    ESt_ratio_eU_eTh
    Contours and labels for equivalent uranium/equivalent thorium ratio (unitless) data (Source: CGG)

    vector file

    ESt_nadr
    Contours and labels for natural air absorbed dose rate [nGy/h (nanogray per hour)] data (Source: CGG)

    vector file

    ESt_FP
    Flight, tie, and border lines, line and flight numbers, tics and labels for the survey lines flown. (Source: CGG)

    vector file

    ESt_SecGrid
    Alaska PLSS Section Grid (original file name 'pls_section') for the map areas. Modified by CGG for line width, color, township and range numbers to use on the maps. (Source: Alaska Department of Natural Resources - Land Records Information Section; L.E. Burns, Division of Geological & Geophysical Surveys; and CGG)

    vector file containing alphanumeric characters

    ESt_UTMGrid
    A UTM grid for the map area produced by CGG. Consists of non-alphanumeric characters placed to look like alphanumeric labels around the edges of the map sheets. (Source: CGG)

    file containing non-alphanumeric characters

    gpr2014-5_Maps_1A-7C_AsPDFS.zip, gpr2014-5_Maps_8A-13C_AsPDFS.zip, gpr2014-5_Maps_14A-21C_AsPDFS.zip, gpr2014-5_Maps_22A-29C_AsPDFS.zip, gpr2014-5_Maps_1A-7C_AsHPGL2.zip, gpr2014-5_Maps_8A-13C_AsHPGL2.zip, gpr2014-5_Maps_14A-21C_AsHPGL2.zip, and gpr2014-5_Maps_22A-29C_AsHPGL2.zip
    Zip file names indicate the map numbers and format included in the zip file. (Source: CGG)

    GPR2014-5-1
    Residual magnetic field with topography. In nanoteslas (nT). (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-2
    Residual magnetic field (nT) and data contours. In nT. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-3
    First vertical derivative with topography. In nT/m. Calculated from the residual magnetic field. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-4
    Analytic signal with topography. In nT/m. Calculated from the residual magnetic field. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-5
    Analytic signal with data contours. In nT/m. Calculated from the residual magnetic field. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-6
    Tilt derivative with topography and data contours. In degrees. Calculated from residual magnetic field. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-7
    Color shadow residual magnetic field with magnetic tilt derivative contours. Color in nT; contours in degrees. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-8
    56,000 Hz apparent coplanar resistivity with topography. In ohm m. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-9
    56,000 Hz apparent coplanar resistivity and data contours. In ohm m. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-10
    7200 Hz apparent coplanar resistivity with topography. In ohm m. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-11
    7200 Hz apparent coplanar resistivity and data contours. In ohm m. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-12
    900 Hz apparent coplanar resistivity with topography. In ohm m. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-13
    900 Hz apparent coplanar resistivity and data contours. In ohm m. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-14
    Equivalent thorium/percent potassium (eTh/K) with topography. In ppm/%. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-15
    Equivalent thorium/percent potassium (eTh/K) and data contours. In ppm/%. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-16
    Uranium/potassium (eU/K) with topography. In ppm/%. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-17
    Uranium/potassium (eU/K) and data contours. In ppm/%. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-18
    Uranium/thorium (eU/eTh) with topography. Unitless. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-19
    Uranium/thorium (eU/eTh) and data contours. Unitless. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-20
    Potassium (K) with topography. In percent. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-21
    Potassium (K) and data contours. In percent. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-22
    Thorium (eTh) with topography. In ppm. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-23
    Thorium (eTh) and data contours. In ppm. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-24
    Uranium (eU) with topography. In ppm. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-25
    Uranium (eU) and data contours. In ppm. (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-26
    Natural air absorbed dose rate with topography. In nGy/h (nanogray per hour). (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-27
    Natural air absorbed dose rate and data contours. In nGy/h (nanogray per hour). (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-28
    Radioelement - Ternary with topography (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-5-29
    Flight Path with topography (Source: CGG)

    map in PDF and HPGL/2 format

    Entity_and_Attribute_Overview:
    The linedata were divided into two separate database files (EStyx_EM.gdb and EStyx_RAD.gdb) for easier downloading. Both files, 'EStyx_EM' and 'EStyx_RAD', contain the same line numbers, fids, and locational data so that the files can be easily merged if wanted by the user. 'EStyx_EM' contains magnetic and electromagnetic data, and 'EStyx_RAD', the radiometric data. These two files are also provided in Geosoft ASCII XYZ formats, where three files for each of the two databases are needed for downloading ease. The 'XYZtoGDB.i0' files define the input fields to convert XYZ files to GDB files. A text file ('EStyx_Linedata.txt') contains some of the linedata information included in this metadata document, but in normal ASCII text format. EStyx_Linedata.txt is included with each downloadable zip file. Each linedata file contains raw and processed linedata, and related calculated fields. Missing data are represented with the dummy variable '*'. Each of the 511 flight lines or partial flight lines (e.g. Line 10010, referred to as 'LINE' attribute) is associated with a 'DATE' (e.g. 2013/07/28), a 'FLIGHT (number)' (e.g. 24145), and a particular multi-record set of data. Each record represents data acquisition from one spatial location in the flight line. A total of 3,764,290 records are present in each data file.
    Entity_and_Attribute_Detail_Citation:
    L.E. Burns, Division of Geological & Geophysical Surveys and Fugro Airborne Surveys
    Entity_and_Attribute_Overview:
    Four map sheets, labeled A through D, are needed to cover the survey at a scale of 1:63,360. The map sheet divisions are shown in gpr2014-005_browsegraphic.pdf. Most geophysical images that were included in a map in this publication are placed on two sets of maps, one with topography and one with data contours and no topography. Maps are provided in PDF and HPGL/2 format, and are downloadable in zip files by data format. The HPGL/2 maps and the Adobe Acrobat format maps are each divided into four files with the range of map numbers included at the end of the file name. The HPGL/2 files have brighter and more gradational colors, and sharper topography than the Adobe Acrobat files. See 'Technical_Prerequisites' section for more information on printing HPGL/2 maps.
    Authors and titles of the maps are like the example given below:
    Burns, L.E., CGG, and Fugro GeoServices, Inc., 2013, Residual magnetic field with topography, Farewell Survey area, south-central Alaska, Talkeetna, Tyonek, McGrath, and Lime Hills quadrangles: Alaska Division of Geological & Geophysical Surveys Geophysical Report 2014-5-1A, 1 sheet, scale 1:63,360.
    Entity_and_Attribute_Detail_Citation:
    L.E. Burns, Division of Geological & Geophysical Surveys, and CGG

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?

Why was the data set created?

The survey was part of the Alaska Airborne Geophysical/Geological Mineral Inventory Program funded by the Alaska State Legislature and managed by State of Alaska, Department of Natural Resources (DNR), Division of Geological & Geophysical Surveys (DGGS). The program seeks to catalyze private-sector mineral development investment. The program 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.

How was the data set created?

  1. From what previous works were the data drawn?

    Akima, 1970 (source 1 of 3)
    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.

    Online Links:

    • None

    Type_of_Source_Media: paper
    Source_Contribution: CGG used a modification of this method while making grids.

    Fraser, 1978 (source 2 of 3)
    Fraser, D.C., 1978, Resistivity mapping with an airborne multicoil electromagnetic system: Geophysics v. 43.

    Online Links:

    • None

    Type_of_Source_Media: paper
    Source_Contribution:
    CGG used this method for calculating apparent depth and apparent resistivity

    ADNR-LRIS, 1995 (source 3 of 3)
    Alaska Department of Natural Resources - Land Records Information Section, 1995, Alaska PLSS Section Grid: State of Alaska, Department of Natural Resources, Division, Land Records Information Section (LRIS), <http://dnr.alaska.gov/lrisservices/ls_proxy/document?static_pickup=pls_section.zip>.

    Online Links:

    Other_Citation_Details: ESRI shape file format
    Type_of_Source_Media: online
    Source_Contribution:
    The downloaded section grid file, built from original protraction diagram data, was used as a starting point for the section grid digital file included in GPR 2014-5. Minor formatting modifications were made to the file. The section grid is used on the maps without topography and is provided in digital format in this publication. The ending date for content, given above, reflects the current metadata file for the Alaska PLSS Section Grid.

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

    Date: 2013 (process 1 of 10)
    The airborne geophysical data were acquired between July 5, 2013 to September 25, 2013 with DIGHEM (V) Electromagnetic (EM) systems, Scintrex CS3 cesium magnetometer sensors, and Radiation Solutions RS-500 256-channel gamma-ray spectrometers. The EM and magnetic sensors were flown at a height of 100 feet, with the magnetic sensor installed in the EM sensor. The spectrometer was flown at 200 ft AGL inside the helicopter. In addition, the survey recorded data from radar and laser altimeters, GPS navigation system, 50/60 Hz monitors, thermometer, barometric pressure instrument, and video camera.
    Flights were performed with three Aerospatiale AS-350-B3 helicopters. All were flown at a mean terrain clearance of 200 feet (61 m). Survey flight lines were flown at a heading of 70 degrees (NE-SW) with one-quarter mile (402.3 m) line spacing). Tie lines were flown at a heading of 340 degrees (NW-SE), perpendicular to the flight lines, and were spaced at intervals of approximately 3 miles (4,828 m).
    Novatel OEM4-G2L Global Positioning Systems were used for navigation and flight path recovery. The helicopter positions were derived every 0.5 seconds (2 Hz); the ground GPS base station data were collected at 1.0 second (1 Hz) intervals. The positional xy data are interpolated from 2 Hz to 10 Hz. The use of the differentially-corrected base station data results in a positional accuracy of better than five meters. Flight path positions were projected onto the Clarke 1866 (UTM zone 5N) 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.

    Date: 2013 (process 2 of 10)
    The total magnetic field data were acquired with a sampling interval of 0.1 seconds. Data are contained in the files 'EStyx_EM.gdb' and 'EStyx_EM.xyz'. The raw magnetic data (channel 'mag_raw') were (1) corrected for measured system lag (resulting in channel 'mag_lag'), (2) corrected for diurnal variations by subtraction of the digitally recorded base station magnetic data (resulting in channel 'mag_diu'), (3) adjusted for regional variations (by subtracting IGRF model 2010, updated for date of flight and elevation variations), (4) leveled to the tie line data resulting in the final residual magnetic intensity (resulting in channel 'mag_rmi'), (5) manually leveled with final small microleveling, and (6) increased by a constant IGRF average value to restore the mag_rmi values to a total magnetic field channel (resulting in channel 'magigrf'). 'Mag_RMI' and 'MagIGRF' were then interpolated onto a regular 80-m grid using a modified Akima (1970) technique.

    Data sources used in this process:

    • Akima, 1970

    Date: 2013 (process 3 of 10)
    Three different algorithms were applied to the total magnetic field 80 m grid, resulting in three magnetic derivative grids. The analytic signal grid ('ESt_ASig') is the total amplitude of all directions of magnetic gradient calculated from the sum of the squares of the three orthogonal gradients. Mapped highs in the calculated analytic signal of the magnetic parameter locate the anomalous source body edges and corners (e.g., contacts, fault/shear zones, basement fault block boundaries or lithologic contacts, etc.). Analytic signal maxima are located directly over faults and contacts, regardless of structural dip, and independently of the direction of the induced and/or remanent body magnetizations.
    The calculated magnetic tilt grid ('ESt_TiltDer') is the angle between the horizontal gradient and the total vertical gradient, and is useful for identifying the depth and type of magnetic source. The tilt angle is positive over the source, crosses through zero at, or near, the edge of a vertical sided source, and is negative outside the source zone. It has the added advantage of responding equally well to shallow and deep sources and is able to resolve deeper sources that may be masked by larger responses caused by shallower sources.
    The first vertical derivative grid was calculated using a fast Fourier transform (FFT)-based frequency-domain filtering algorithm. The vertical gradient algorithm enhances the response of magnetic bodies in the upper 500 m and attenuates the response of deeper bodies. The resulting (calculated) vertical gradient grid ('ESt_1VD') provides better definition and resolution of near-surface magnetic units and helps to identify weak magnetic features that may not be evident in the total field data.
    All magnetic and derivative magnetic grids were then resampled from the 80-m cell size down to a 25-m cell size using a modified Akima (1970) technique to produce the maps and final grids contained in this publication. When resampling the grids to a 25-m cell size, the original grids are scanned to determine the minimum and maximum values which the new grids are then limited to, avoiding extreme extrapolation errors between lines.

    Data sources used in this process:

    • Akima, 1970

    Date: 2013 (process 4 of 10)
    The DIGHEM (V) EM systems measured inphase and quadrature components at five frequencies. Two vertical coaxial-coil pairs operated at nominal frequencies of 1000 and 5500 Hz while three horizontal coplanar-coil pairs operated at 900, 7200, and 56,000 Hz. Information provided by CGG and shown in the four tables below provides the actual frequencies used for the three EM systems.
    Table 1 -- DIGHEM(V) EM SYSTEM AND FLIGHTS BKS51: Flights 24095:24249 BKS52: Flights 20030 and 4035:4069 BKS52_after Jul 15: Flights 4072:4188 BKS54: Flights 29024:29029
    Table 2 -- DIGHEM(V) BKS51 CONFIGURATION
    Coil Tx-Rx Nominal Operating Pair Orientation separation frequency frequency 1 coaxial 8.0 m 1,000 Hz 1,120 Hz 2 coplanar 8.0 m 7,200 Hz 7,303 Hz 3 coplanar 8.0 m 900 Hz 925 Hz 4 coaxial 8.0 m 5,500 Hz 5,394 Hz 5 coplanar 6.4 m 56,000 Hz 55,450 Hz
    Table 3 -- DIGHEM(V) BKS52 CONFIGURATION (* = 909.3 Hz after July 15, 2013)
    Coil Orien- Tx-Rx Nominal Operating Pair Orientation separation frequency frequency 1 coaxial 8.0 m 1,000 Hz 1,162 Hz 2 coplanar 8.0 m 7,200 Hz 7,284 Hz 3 coplanar 8.0 m 900 Hz 890* Hz 4 coaxial 8.0 m 5,500 Hz 5,926 Hz 5 coplanar 6.4 m 56,000 Hz 55,380 Hz
    Table 4 - DIGHEM(V) BKS54 CONFIGURATION Coil Tx-Rx Nominal Operating Pair Orientation separation frequency frequency 1 coaxial 8.0 m 1,000 Hz 1,140 Hz 2 coplanar 8.0 m 7,200 Hz 7,020 Hz 3 coplanar 8.0 m 900 Hz 883.6 Hz 4 coaxial 8.0 m 5,500 Hz 5,730 Hz 5 coplanar 6.4 m 56,000 Hz 56,260 Hz

    Date: 2014 (process 5 of 10)
    EM data were sampled at 0.1 second intervals. The EM system responds to bedrock conductors, conductive overburden, and cultural sources. The EM inphase and quadrature data were drift-corrected using base level data collected at high altitude (areas of no signal). Along-line filters are 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.
    The apparent resistivity and depth were then calculated from the inphase and quadrature data for all coplanar frequencies. The calculation used the pseudo-layer (or buried) half-space model defined by Fraser (1978). This model consists of a resistive layer overlying a conductive half-space. The apparent depth is defined as the sensor-source distance minus the measured altitude of the sensor above the ground. The apparent depth channels estimate the depth below surface of a conductive half-space and are the apparent thickness of the overlying resistive layer. The apparent depth (or thickness) parameter will be positive when the upper layer is more resistive than the underlying material, in which case the apparent depth may be quite close to the true depth assuming it is a buried halfspace and altimeter is correct. The apparent depth will be negative when the upper layer is more conductive than the underlying material, and will be zero when a homogeneous half-space exists. The apparent depth parameter must be interpreted cautiously because it will contain any errors that might exist in the measured altitude of the EM bird (e.g., as caused by a dense tree cover). 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 is carried out in areas of low signal.
    The EM data were interpolated onto a regular 80-m grid using a modified Akima (1970) technique. The resulting grids were subjected to a 3x3 Hanning filter and resampled to a 25-m cell size before contouring and map production. When re-sampling the grids to a 25-m cell size, the original grids are scanned to determine the minimum and maximum values which the new grids are then limited to, avoiding extreme extrapolation errors between lines.

    Data sources used in this process:

    • Frasier, 1978
    • Akima, 1970

    Date: 2014 (process 6 of 10)
    The gamma-ray spectrometry data were recorded at a 1.0 second sample rate using a Radiation Solutions RS-500 gamma-ray spectrometer. It was configured with 16.8L (1024 cubic inches) of main (downward) NaI crystal detector, and 4.2L (256 cubic inches) of upward looking (radon) detector. After application of Noise Adjusted Singular Value Decomposition to the spectra, counts from the main detector were recorded in five windows corresponding to thorium (2410-2810 keV), uranium (1660-1860 keV), potassium (1370-1570 keV), total radioactivity (400-2815 keV) and cosmic radiation (3000->6000 keV). Counts from the radon detector were recorded in the radon window (1660-1860 keV). The radon detection system was calibrated following methods outlined in IAEA Report 1363. After removal of the background, the data were corrected for spectral interferences, changes in temperature, pressure, and departures from the planned survey elevation of 200 feet. The data were then converted to standard concentration units which were interpolated to a 100-m grid using a minimum curvature technique. All grids were then resampled from the 100-m cell size down to a 25-m cell size to produce the maps and final grids contained in this publication. When re-sampling the grids to a 25-m cell size, the original grids are scanned to determine the minimum and maximum values which the new grids are then limited to, avoiding extreme extrapolation errors between lines.

    Data sources used in this process:

    • IAEA TECDOC-1363, 2003
    • CGG, 2014
    • Akima, 1970

    Date: 2013 (process 7 of 10)
    The digital elevation/terrain model was produced from the differentially corrected GPS-Z data (channel 'GPSZ' in linedata files 'EStyx_EM' and 'EStyx_RAD') and the laser altimeter data measured in the bird (channel 'ALTLAS_BIRD' included in the same files). Both the GPSZ and ALTLAS_BIRD data were checked for spikes, which were removed manually. The ALTLAS_BIRD data were despiked and then filtered using a 13 median filter, followed by a 13 Hanning filter. The corrected altimeter data were then subtracted from the GPSZ data to produce profiles of the height above mean sea level along the survey lines. The data were manually leveled to remove any errors between lines. After all leveling, the data were DC shifted to match the local maps, in this case, NAD27. The 80-m DTM grid was then resampled to a 25-m cell size to produce the DTM grid contained in this publication.

    Data sources used in this process:

    • Akima, 1970

    Date: 2014 (process 8 of 10)
    Fugro Airborne Surveys downloaded the Alaska PLSS Section Grid shapefile in fall 2008 and subset this in-house version to roughly fit the map sheets for this publication using MapInfo Professional. CGG modified the formatting of the file using AutoCad, changing township and range line widths and colors, and added township and range labels. The modified file was then used as overlays on maps without topography.

    Data sources used in this process:

    • ADNR-LRIS, 1995

    Date: 2014 (process 9 of 10)
    All grids with 25 m cell size and the radiometric ternary diagram were converted to Geotiffs and KMZs using CGG's specialized software. The 80 m cell size grids for the 56,000, 7200, and 900 coplanar grids were also converted to Geotiffs and KMZs.

    Date: 2014 (process 10 of 10)
    The HPGL/2 files were created with HP Designjet T1300ps HPGL driver, and plot on some plotters, but not all plotters correctly. The Adobe Acrobat format files were created with Adobe Acrobat Distiller v9.0 from Postscript files.

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

    Burns, L.E., Fugro Airborne Surveys Corp., and Stevens Exploration Management Corp., 2008, Line, grid, and vector data and plot files for the airborne geophysical survey of the Styx River Survey, southcentral Alaska: Geophysical Report GPR 2008-3, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), Fairbanks, AK, USA.

    Online Links:

    Other_Citation_Details: 1 DVD
    Burns, L.E., Fugro Airborne Surveys Corp., and Fugro GeoServices, Inc., 2013, MIDDLE STYX SURVEY AREA: Airborne Magnetic, Electromagnetic, and Radiometric Data in Line (Point), Grid, Vector, and Map formats, Lime Hills and Tyonek quadrangles, southcentral Alaska: Geophysical Report GPR 2013-2, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), Fairbanks, AK, USA.

    Online Links:

    Other_Citation_Details: 1 DVD
    Burns, L.E., CGG, and Fugro GeoServices, Inc., 2014, FAREWELL SURVEY: Airborne Magnetic, Electromagnetic, and Radiometric Data in Line (Point), Grid, Vector, and Map formats, McGrath and Lime Hills quadrangles, south-central Alaska: Geophysical Report GPR 2014-2, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), Fairbanks, AK, USA.

    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?

    Survey contracts specified the conditions and specifications under which these data were collected. Altimeter, heading, lag, and frequent EM calibrations were done. More information will be available in the project report to be published in the future.

  2. How accurate are the geographic locations?

    The helicopter position was derived every 0.5 seconds using post-flight differential positioning to an accuracy of better than 1 m.

  3. How accurate are the heights or depths?

    The laser altimeter ('ALTLAS_BIRD'), located in the bird (EM equipment and magnetometer housing), had a stated resolution of 0.10 meter. The ALTLAS_BIRD value may be unreliable over bodies of water where the laser returns are scattered.

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

    The linedata files EStyx_EM and EStyx_RAD each contain 3,764,290 records. The radiometric data, sampled every 1.0 seconds, produced a maximum of 376,429 sample points, a tenth of the total maximum records. The apparent resistivity values are missing for 254,511 points, and are due to terrain and the need to fly too high to resolve electromagnetic data with accuracy. The calculated depths for the apparent resistivities have more null values than the calculated apparent resistivity.

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

    Ownership of Fugro Airborne Surveys was changed from Fugro to CGG during the course of this contract. The same office, management, personnel, methods, and attention to detail continued. The change was seamless. Fugro Airborne Surveys, and then CGG was responsible for collecting and processing the data. All the data were collected with the same instruments (magnetometers, electromagnetic bird and sensors, gamma ray spectrometer, altimeters, and navigational system).

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 &amp; 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 2014-5

  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?

    Software with ability to use, import, or convert Geosoft float GRD, Geosoft binary GDB or ASCII XYZ files, Autocad DXF files, ESRI Shape files, Adobe Acrobat PDF, Google Earth files, and text files. Free downloadable interfaces to view or convert the gridded and dxf files are available at the Geosoft Web site (<http://www.geosoft.com>; Oasis Montaj viewer). The KMZ files can be dragged and dropped into the 'My Places' folder of the free downloadable 'Google Earth' software. Freeware software 'printfile' (<http://www.lerup.com/printfile/>) prints HPGL/2 files easily on compatible printers. The HPGL/2 files have brighter colors and sharper topography than the PDF maps and should be used for printing when possible. Unfortunately, Postscript printers and plotters turn the HPGL/2 files into a format like PDF, and thus decrease the color vitality and the sharpness. The PDF format maps are the only maps digitally viewable in this publication.

Who wrote the metadata?

Dates:
Last modified: 03-Nov-2014
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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