Wrangellia survey area: Airborne magnetic and electromagnetic data in line (point), grid, vector, and map formats, Talkeetna Mountains, Healy, and Mt. Hayes quadrangles, south-central Alaska

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Frequently anticipated questions:

What does this data set describe?

Title:
Wrangellia survey area: Airborne magnetic and electromagnetic data in line (point), grid, vector, and map formats, Talkeetna Mountains, Healy, and Mt. Hayes quadrangles, south-central Alaska
Abstract:
This digital publication, GPR 2014-1, contains data produced from airborne geophysical surveys conducted in 2013 for the Talkeetna Mountains, Healy, and Mt. Hayes quadrangles in south-central Alaska. The area is in the Valdez Creek and Delta River mining districts. Aeromagnetic and electromagnetic (EM) data were acquired by helicopter for about 1310 sq miles, and additional data donated by Millrock Exploration Corporation, Anchorage, increased coverage by about 12 sq miles. Millrock also provided some infill flight lines for over a similar amount of sq miles. CGG acquired and processed all the airborne geophysical data. The data were all flown with the same systems and contract specifications. CGG's frequency-domain DIGHEM V system was used for the EM data. GPR 2014-1 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; (4) vector files of data contours and flight lines. Supporting files include gpr2014_001_readme.txt, Wrangellia_Linedata.txt, gpr2014_001_browsegraphic.pdf, and individual jpgs of some of the items in the browsegraphic file.
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. A future publication will 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_001_readme.pdf'. 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. Page-sized location figures and images of the data are provided in the gpr2014_001_browsegraphic.pdf file, and as jpegs on the DVD version and through each download. The file 'Wrangellia_001_linedata.txt' gives information on the linedata in an easy-to-read format. All data are provided in NAD27, UTM zone 6N, except for Google Earth KMZ files, which are in Geographic Coordinate System (Simple Cylindrical projection) with a WGS84 datum. Besides NAD27, UTM zone 6N 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, Wrangellia survey area: Airborne magnetic and electromagnetic data in line (point), grid, vector, and map formats, Talkeetna Mountains, Healy, and Mt. Hayes quadrangles, south-central Alaska: Geophysical Report GPR 2014-1, 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: -148.71
    East_Bounding_Coordinate: -146.12
    North_Bounding_Coordinate: 63.37
    South_Bounding_Coordinate: 62.57

  3. What does it look like?

    gpr2014_001_browsegraphic.pdf (PDF)
    The browse graphic file contains three location maps showing: 1) survey area and adjacent published surveys within Alaska, 2) detailed location diagram showing the survey area and adjacent surveys, 3) detailed diagram showing map sheets at 1:63,360-scale, and location of the area partially donated by Millrock; 4) diagram showing flight directions over the three major survey blocks, and 5) several page-sized images of data.

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

    Beginning_Date: Jun-2013
    Ending_Date: Jan-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: 6
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -147
      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?

    WrangelliaLinedataAsGDB_Part1.ZIP and WrangelliaLinedataAsGDB_Part2.ZIP
    The linedata files contain raw and processed data and related calculated fields for locational, magnetic, and electromagnetic data. The linedata are provided in Geosoft binary GDB format, and are split into two parts to allow for easier downloading. The file labeled with 'Part1' contains data for Blocks 2 and 3; 'Part2' contains data for Blocks 4 and 1, as well as all of the tie and border line data (see 'gpr2014_001_browsegraphic.pdf', figure 3). Supporting information about the data is included in the file 'Wrangellia_Linedata.txt'. (Source: L.E. Burns & CGG)

    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., 'L20010:29003' and 'T29010:29086'). More than one line is typically flown on a particular date and flight; more than one flight may be flown on a particular date. The first digit of the 'LINE' attribute corresponds to the Block number. 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 29003
  //Date 2013/06/30
  Line 20010  (or 'Tie 29010' instead of 'Line 20010' when appropriate)
  Followed by all records for points sampled along Line 20010.
     (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 & CGG)

    Definitions of the 'FLIGHT' attributes are listed with the 'flight' attribute label below.

    x_NAD27z6N
    easting NAD 27 (UTM Zone 6) (Source: CGG)

    Range of values
    Minimum:414392.19
    Maximum:545408.53
    Units:m

    y_NAD27z6N
    northing NAD 27 (UTM Zone 6) (Source: CGG)

    Range of values
    Minimum:6937667.50
    Maximum:7027550.40
    Units:m

    fid
    Fiducial increment; the time in tenths of seconds from the start to the end of the particular flight. (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:62.5647087
    Maximum:63.3774650
    Units:degrees

    lon_WGS84
    longitude WGS 84 (Source: CGG)

    Range of values
    Minimum:-148.6760665
    Maximum:-146.1032101
    Units:degrees

    flight
    The attribute 'flight' is actually a compound designator indicating the identification of the HeliDAS (Data Acquisition System), in this case '29', followed by 3 digits indicating the actual flight number. A flight number is the sequential numbering of the helicopter flight from home base to home base associated with a survey. These result in a 5 digit number, e.g. 29003. An exception has been made for the flights for Block 1, which was flown after DGGS Block 2, 3, and 4. Block 1 was considered a separate project by CGG and flight numbering was restarted at the beginning. To make the flight number unique for all the flights, a '1' was placed in front of the 5 digit number for Block 1. Only those flight numbers containing acquisition of final data measurements are included in the database. (Source: CGG)

    See 'Wrangellia_Linedata.txt' for more information.

    date
    range of flight dates (yyyy/mm/dd) for production flights of the survey (Source: CGG)

    Range of values
    Minimum:2013/06/30
    Maximum:2013/08/27
    Units:day

    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, which represented distance in altitude from helicopter to the bird when towing and recording data. (Source: CGG)

    Range of values
    Minimum:11.34
    Maximum:492.88
    Units:m

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

    Range of values
    Minimum:12.05
    Maximum:564.07
    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:512.15
    Maximum:2196.41
    Units:m

    dtm
    digital terrain model (NAD27 UTM zone 6); calculated from channel 'GPS-Z' and the laser data (channel 'ALTLAS_BIRD') measured in the bird ' (Source: CGG)

    Range of values
    Minimum:472.32
    Maximum:2166.88
    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:55735.60
    Maximum:56369.27
    Units:nT

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

    Range of values
    Minimum:-495.4
    Maximum:138.27
    Units:nT

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

    Range of values
    Minimum:54612.78
    Maximum:62348.25
    Units:nT

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

    Range of values
    Minimum:54613.87
    Maximum:62348.25
    Units:nT

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

    Range of values
    Minimum:54571.08
    Maximum:62318.09
    Units:nT

    igrf
    international geomagnetic reference field (Source: CGG)

    Range of values
    Minimum:56311.60
    Maximum:56838.55
    Units:nT

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

    Range of values
    Minimum:-2091.69
    Maximum:5868.86
    Units:nT

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

    Range of values
    Minimum:54714.81
    Maximum:62675.36
    Units:nT

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

    Range of values
    Minimum:-718.15
    Maximum:1020.36
    Units:ppm

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

    Range of values
    Minimum:-18.78
    Maximum:644.83
    Units:ppm

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

    Range of values
    Minimum:-198.57
    Maximum:293.05
    Units:ppm

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

    Range of values
    Minimum:-13.61
    Maximum:175.95
    Units:ppm

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

    Range of values
    Minimum:-171.98
    Maximum:384.65
    Units:ppm

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

    Range of values
    Minimum:-28.10
    Maximum:326.09
    Units:ppm

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

    Range of values
    Minimum:-485.75
    Maximum:1244.62
    Units:ppm

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

    Range of values
    Minimum:-106.08
    Maximum:842.20
    Units:ppm

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

    Range of values
    Minimum:-320.14
    Maximum:1712.89
    Units:ppm

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

    Range of values
    Minimum:-108.41
    Maximum:1214.21
    Units:ppm

    cpi900
    coplanar inphase 900 Hz (Source: CGG)

    Range of values
    Minimum:-718.34
    Maximum:1027.93
    Units:ppm

    cpq900
    coplanar quadrature 900 Hz (Source: CGG)

    Range of values
    Minimum:-3.40
    Maximum:644.87
    Units:ppm

    cxi1000
    coaxial inphase 1000 Hz (Source: CGG)

    Range of values
    Minimum:-198.58
    Maximum:289.59
    Units:ppm

    cxq1000
    coaxial quadrature 1000 Hz (Source: CGG)

    Range of values
    Minimum:-1.55
    Maximum:175.92
    Units:ppm

    cxi5500
    coaxial inphase 5500 Hz (Source: CGG)

    Range of values
    Minimum:-174.26
    Maximum:376.78
    Units:ppm

    cxq5500
    coaxial quadrature 5500 Hz (Source: CGG)

    Range of values
    Minimum:-17.04
    Maximum:328.98
    Units:ppm

    cpi7200
    coplanar inphase 7200 Hz (Source: CGG)

    Range of values
    Minimum:-485.81
    Maximum:1244.59
    Units:ppm

    cpq7200
    coplanar quadrature 7200 Hz (Source: CGG)

    Range of values
    Minimum:-4.16
    Maximum:842.18
    Units:ppm

    cpi56k
    coplanar inphase 56k Hz (Source: CGG)

    Range of values
    Minimum:-320.12
    Maximum:1713.06
    Units:ppm

    cpq56K
    coplanar quadrature 56k Hz (Source: CGG)

    Range of values
    Minimum:-2.00
    Maximum:1227.30
    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:0.89
    Maximum:1325
    Units:ohm�m

    res7200
    apparent resistivity 7200 Hz; cut-off value for apparent resistivity was 110750; more information in Process_Steps (Source: CGG)

    Range of values
    Minimum:3.33
    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:5.87
    Maximum:60000
    Units:ohm�m

    dep900
    apparent depth 900 Hz; more information in Process_Steps. (Source: CGG)

    Range of values
    Minimum:-111.74
    Maximum:291.99
    Units:m

    dep7200
    apparent depth 7200 Hz; more information in Process_Steps. (Source: CGG)

    Range of values
    Minimum:-119.06
    Maximum:140.64
    Units:m

    dep56K
    apparent depth 56k Hz; more information in Process_Steps. (Source: CGG)

    Range of values
    Minimum:-128.89
    Maximum:114.23
    Units:m

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

    Range of values
    Minimum:-73.35
    Maximum:154.78
    Units:unitless

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

    Range of values
    Minimum:-32.37
    Maximum:203.45
    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

    gpr2014-1_GRIDSasERS_NAD27_z6N.zip, gpr2014-1_GRIDSasGRD_NAD27_z6N.zip, gpr2014-1_GEOTIFFS_NAD27_z6N.zip, and gpr2014-1_KMZS_WGS84.zip
    These zip files contain the 10 grids, 10 geotiffs, and 9 KMZs for the Wrangellia area. Because definitions of the data in each are the same, they are combined in this section. Definitions are below the brief discussion of the different formats and their relationship to each other. A data image was made from each of the different 10 grid files and each data image is provided with corresponding color bar in the Geotiffs and KMZ files. The AltLasBird image is not shown as a KMZ file. One of the following seven data images, Wran_magRMI, Wran_1VD, Wran_Asig, Wran_TiltDer, Wran_res56k, Wran_res7200, and Wran_res900, are used on 13 of the 14 maps in this publication. Four sheets are needed for each map. In contrast, the images shown in the Geotiff or KMZ files show the entire survey area. The 14th map includes flight lines and no data images. The zip files gpr2014-1_GRIDSasGRD_NAD27_z6N.zip and gpr2014-1_GRIDSasERS_NAD27_z6N.zip contain the 10 grids and supporting files for this publication in either Geosoft binary float (GRD) format or ER Mapper (ERS) format. Each grid is in NAD27 datum, UTM Zone 6N, and has a 25m cell size with x and y in meters. 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. The Geotiffs and the Google Earth KMZs will automatically open in the correct projection in a GIS program or Google Earth respectively. (Source: CGG)

    Wran_MagRMI
    Residual magnetic field (nT) - final; IGRF model 2010, updated for date of flight and elevation variations, was subtracted from Mag_Diu, then the data were leveled. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    Wran_MagIGRF
    Total magnetic field (nT) - final, with IGRF removed; residual magnetic field (Mag_RMI) with constant added back in. Not produced as a map. Wran_RMI (also produced as maps) is directly the same as Wran_MagIGRF except off by a constant. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    Wran_1VD
    First vertical derivative 'dz' (nT/m) of the total magnetic field with IGRF removed; also referred to as 'calculated vertical gradient' (cvg). (Source: CGG)

    Grid file, Geotiff file, KMZ file

    Wran_ASig
    Analytic signal (nT/m) calculated from the total magnetic field with IGRF removed. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    Wran_TiltDer
    Tilt derivative (degrees) of the total magnetic field with IGRF removed. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    Wran_Res56k
    Apparent coplanar resistivity (ohm-m) for 56,000 (56k) Hz.; calculated using a pseudo-layer half-space model. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    Wran_Res7200
    Apparent coplanar resistivity (ohm-m) for 7200 Hz.; calculated using a pseudo-layer half-space model. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    Wran_Res900
    Apparent coplanar resistivity (ohm-m) for 900 Hz.; calculated using a pseudo-layer half-space model. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    Wran_DTM
    Digital terrain or elevation model (m). Not shown as a map. (Source: CGG)

    Grid file, Geotiff file, KMZ file

    Wran_AltLasBird
    EM bird height (m) above surface, measured by Laser altimeter in EM bird. Not shown as a map. (Source: CGG)

    Grid file, Geotiff file

    gpr2014-1_VECTORSasDXF_NAD27_z6N.zip and gpr2014-1_VECTORSasSHP_NAD27_z6N.zip
    Data contours produced for the maps are provided in Autocad DXF and ESRI shape file format. Except for maps GPR 2014-1-6 and GPR2014-1-7, 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. Wran_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. Wran_magRMI_1, Wran_magRMI_2, Wran_magRMI_3, and Wran_magRMI_4). Most sets of shape files in this publication contain up to 5 files. 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 10050 would be represented by 5 individual characters instead of one number.
    (Source: CGG)

    Wran_magRMI
    Contours, "triangles" denoting direction of lower values, and labels for the residual magnetic field data (Source: CGG)

    vector file

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

    vector file

    Wran_TiltDer
    Contours and labels for the magnetic tilt derivative data contours are provided at specific values to aid in interpretation of approximate contact location '0' contour), and depth to contact. Contours include the values -45, -30, -15, 0, +15, +30, and +45. (Source: CGG)

    vector file

    Wran_Res56k
    Contours and labels for the 56,000 Hz coplanar apparent resistivity data (Source: CGG)

    vector file

    Wran_Res7200
    Contours and labels for the 7200 Hz coplanar apparent resistivity data (Source: CGG)

    vector file

    Wran_Res900
    Contours and labels for the 900 Hz coplanar apparent resistivity data (Source: CGG)

    vector file

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

    vector file containing lines for all flight lines

    Wran_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

    Wran_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 alphanumeric characters

    gpr2014-1_MAPS_1A-7B_asPDF.zip, gpr2014-1_MAPS_7C-14D_asPDF.zip, gpr2014-1_MAPS_1A-7B_asHPGL2.zip, and gpr2014-1_MAPS_7C-14D_asHPGL2.zip
    Zip file names indicate the map numbers and format included in the zip file. (Source: CGG)

    GPR2014-1-1A, B, C, and D
    Residual magnetic field (nT) with IGRF removed (includes topography). (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-1-2A, B, C, and D
    Residual magnetic field (nT) with IGRF removed (includes data contours). (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-1-3A, B, C, and D
    First vertical derivative (nT/m) of the total magnetic field with IGRF removed (includes topography). (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-1-4A, B, C, and D
    Analytic signal (nT/m) calculated from the total magnetic field with IGRF removed (includes topography). (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-1-5A, B, C, and D
    Analytic signal (nT/m) calculated from the total magnetic field with IGRF removed (includes data contours). (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-1-6A, B, C, and D
    Tilt derivative (degrees) of the total magnetic field with IGRF removed (includes data contours and topography). (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-1-7A, B, C, and D
    Shadowed residual magnetic field (nT with IGRF removed with tilt derivative contours (includes data contours). (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-1-8A, B, C, and D
    Apparent coplanar resistivity (ohm-m) for 56,000 (56k) Hz. (includes topography). (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-1-9A, B, C, and D
    Apparent coplanar resistivity (ohm-m) for 56,000 (56k) Hz. (includes data contours). (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-1-10A, B, C, and D
    Apparent coplanar resistivity (ohm-m) for 7200 Hz. (includes topography). (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-1-11A, B, C, and D
    Apparent coplanar resistivity (ohm-m) for 7200 Hz. (includes data contours). (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-1-12A, B, C, and D
    Apparent coplanar resistivity (ohm-m) for 900 Hz. (includes topography). (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-1-13A, B, C, and D
    Apparent coplanar resistivity (ohm-m) for 900 Hz. (includes data contours). (Source: CGG)

    map in PDF and HPGL/2 format

    GPR2014-1-14A, B, C, and D
    Flight lines (includes topography). (Source: CGG)

    map in PDF and HPGL/2 format

    Entity_and_Attribute_Overview:
    Maps are provided in PDF and HPGL/2 format, and are downloadable in zip files by data format. Both the PDF and the HPGL/2 maps are split into two downloads to minimize download size. The range of map numbers is 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.
    Fourteen maps are included for the area. All maps in this publication are at a scale of 1:63,360 (inch-to-a-mile). Four map sheets are needed to cover the survey area. Figure 2 of the file gpr2014-1-001_graphic.pdf shows the location of Sheets A through D.
    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 through the DGGS Airborne Geophysical/Geological Mineral Inventory (AGGMI) program. A donation of data from Millrock Exploration Corporation, Anchorage, AK, provided increased resolution of some of the area and increased coverage by about 12 sq miles.

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

Why was the data set created?

The survey was part of the Strategic and Critical Minerals Capital Improvement Project (CIP), a subset of the Alaska Airborne Geophysical/Geological Mineral Inventory Program. The program was 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), Anchorage, Alaska.

    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 GPR2014-1. 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 7)
    The airborne geophysical data were acquired between June 15 to August 27, 2013 with a DIGHEM (V) Electromagnetic (EM) system and a Scintrex CS3 cesium magnetometer sensor. The EM and magnetic sensors were flown at a height of 100 feet, with the magnetic sensor installed in the EM bird. In addition, the survey recorded data from radar and laser altimeters, GPS navigation system, 50/60 Hz monitors, and video camera.
    Flights were performed with an Aerospatiale AS-350-B3 helicopter at a mean terrain clearance of 200 feet (61 m). Three flight directions were used for the Wrangellia survey in an attempt to remain perpendicular to the regional structural and geologic trends (Fig. 4). Survey flight lines were flown a heading of 135 (NW-SE) in the Block 2, the western part; 162 (NW-SE) in Block 3, the central part; and N-S for Blocks 4 and 1, the eastern part. Traverse lines were spaced at one-quarter mile (402.3 m) intervals for all the DGGS planned survey area. Millrock provided data flown with one-eighth mile flight lines for Block 1, which includes the far northern part and infill lines between existing DGGS flight lines for a small portion south of that area (see gpr2014_001_browsegraphic.pdf, figure 3). Tie lines were flown perpendicular to flight lines, and were spaced at intervals of approximately 3 miles (4,828 m).
    A Novatel OEM5-G2L Global Positioning System was used for navigation and flight path recovery. The helicopter position was derived every 0.5 seconds (2 Hz); the ground GPS base station data were collected at 1.0 second (1 Hz) intervals. The use of the differentially-corrected base station data results in a positional accuracy of better than five meters. The positional xy data are interpolated from 2 Hz to 10 Hz. Flight path positions were projected onto the Clarke 1866 (UTM zone 6N) spheroid, 1927 North American datum using a central meridian (CM) of 147 degrees, a north constant of 0, and an east constant of 500,000.

    Date: 2013 (process 2 of 7)
    The total magnetic field data were acquired with a sampling interval of 0.1 seconds. Data are contained in channels in the linedata file 'Wrangellia'. The spike-rejected raw magnetic data (channel 'mag_raw') were (1) corrected for measured system lag (resulting in the channel 'mag_lag'), (2) corrected for diurnal variations by subtraction of the digitally recorded base station magnetic data (resulting in the 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 7)
    Three different algorithms were applied to the total magnetic field 80 m grid, resulting in three magnetic derivative grids. The analytic signal grid (Wran_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 (Wran_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 (Wran_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.

    Data sources used in this process:

    • Akima, 1970

    Date: 2013 (process 4 of 7)
    The EM system measured inphase and quadrature components with two vertical coaxial-coil pairs (1000 and 5500 Hz), and three horizontal coplanar-coil pairs (900, 7200 and 56,000 Hz). See 'Wrangellia_Linedata.txt� for information about the operating frequencies. 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. Apparent resistivities were then calculated from the inphase and quadrature data for all coplanar 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 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.

    Data sources used in this process:

    • Akima, 1970

    Date: 2013 (process 5 of 7)
    The digital elevation/terrain model was produced from the differentially corrected GPS-Z data (channel 'GPSZ' in linedata files) and the laser altimeter data measured in the bird (channel 'ALTLAS_BIRD' in linedata). 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 was 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.

    Date: 2013 (process 6 of 7)
    DGGS downloaded the Alaska PLSS Section Grid shapefile in December 2012 and cut the file to roughly fit the map sheets for this publication using MapInfo Professional. Fugro Airborne Surveys 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 7 of 7)
    The HPGL/2 files were created with HP Designjet T1300ps HPGL driver v61.132.2518.500 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?

    Staff, DGGS, Dighem, and WGM, Inc., 1998, CD-ROM containing profile and gridded data and section lines of the 1997 geophysical survey data for Iron Creek area, Talkeetna Mountains Quadrangle, southcentral Alaska: Public Data File PDF 98-9, 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., U.S. Bureau of Land Management Corp., Fugro Airborne Surveys Corp., and Stevens Exploration Management Corp., 2003, Line, grid, and vector data of airborne geophysical survey data for the southern Delta River area, east-central Alaska: Geophysical Report GPR 2003-6, 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., U.S. Bureau of Land Management Corp., Fugro Airborne Surveys Corp., and Stevens Exploration Management Corp., 2003, Plot files of the airborne geophysical survey data of the southern Delta River area, east-central Alaska: Geophysical Report GPR 2003-5, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), Fairbanks, AK, USA.

    Online Links:

    Other_Citation_Details: 1 DVD
    Pritchard, R.A., 2003, Project report of the airborne geophysical survey for the southern Delta River area, east-central Alaska: Geophysical Report GPR 2003-7, 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., U.S. Bureau of Land Management Corp., Fugro Airborne Surveys Corp., and Stevens Exploration Management Corp., 2004, Line, gridded, and vector data, and selected plot files of the airborne geophysical survey data of the Valdez Creek mining district, central Alaska: Geophysical Report GPR 2004-3, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), Fairbanks, AK, USA.

    Online Links:

    Other_Citation_Details: 1 DVD
    McConnell, D.L., 1994, Final summary of 1993 airborne geophysical surveys of the Nome, Circle, Nyac, and Valdez Creek areas: Public Data File PDF 94-36, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), Fairbanks, AK, USA.

    Online Links:

    Other_Citation_Details: 327 p., 4 sheets, scale 1:63,360

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 file has missing values for the calculated apparent resistivity and apparent depth channels. These are due to an increased altitude that renders the calculations meaningless. More information is in 'Wrangellia__Linedata.txt'.

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

    Data for this survey were collected by a single subcontractor (CGG) who was responsible for collecting and processing the data. One helicopter, one EM system, and one airborne magnetometer were used. The data donated by Millrock Exploration Corporation was flown by CGG immediately after the DGGS survey was finished. CGG continued using the specifications and processing of the data that were used with the DGGS data. Operational frequencies for the EM system varied and are documented in 'Wrangellia_Linedata.txt'.

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 2014-1

  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. Is there some other way to get the data?

    DGGS publications are available as free online downloads or you may purchase paper hard-copies or digital files on CD/DVD or other digital storage media over the counter, by mail, phone, fax, or email from the DGGS Fairbanks office. Turnaround time is 1-2 weeks unless special arrangements are made and an express fee is paid. Shipping charge will be the actual cost of postage and will be added to the total amount due. Contact us for exact shipping amount.

  6. 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, MapInfo Professional TAB 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. The PDF format maps are the only maps digitally viewable in this publication.

Who wrote the metadata?

Dates:
Last modified: 30-Jan-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:

Generated by mp version 2.9.21 on Thu Jan 30 10:48:26 2014