IDITAROD SURVEY AREA: Magnetic and Electromagnetic Line, Grid, and Vector Data and Maps, Innoko, Iditarod, and Ophir mining districts, Iditarod and Ophir quadrangles, western Alaska (DIGHEM [V] SURVEY)

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Title:
IDITAROD SURVEY AREA: Magnetic and Electromagnetic Line, Grid, and Vector Data and Maps, Innoko, Iditarod, and Ophir mining districts, Iditarod and Ophir quadrangles, western Alaska (DIGHEM [V] SURVEY)
Abstract:
This digital publication, GPR 2011-2, contains data produced from airborne geophysical surveys conducted in 2010 for the Iditarod survey area in the Innoko, Iditarod, and Ophir mining districts, Iditarod and Ophir quadrangles, western Alaska. Aeromagnetic and electromagnetic (EM) data were acquired by helicopter for about 852 sq miles. Fugro Airborne Survey's frequency-domain DIGHEM V system was used for the EM data. GPR 2011-2 includes (1) raw and processed linedata; (2) gridded, Google Earth, and Geotiff formats of the calculated linedata; (3) maps of the data; 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. Fugro Airborne Surveys, the subcontractor, acquired and processed the data in 2010 and 2011. A future publication will include the technical project report, interpretation map, and EM anomalies, as well as other files.

File 'gpr2011-002_readme.PDF' contains file names and definitions, map numbers and grid correlations, projection information, location figures, and much general information. In case the text version of 'gpr2011-002_readme.txt' needs to be used, the location figures are provided as jpegs in the main directory. Some detailed information about the data is given in the 'Entity_and_Attribute_Information' section of this metadata file. 'Iditarod_linedata.txt' gives information on the linedata in an easy-to-read format. All data are provided in NAD27, UTM zone 4N, except for Google Earth KMZ files, which are in Geographic Coordinate System (Simple Cylindrical projection) with a WGS84 datum. Besides NAD27, UTM zone 4N easting and northing coordinates, the linedata files also include latitude and longitude (Geographic Coordinate System with a WGS84 datum).

This publication, GPR2011-2, contains the data types or files given below

***********************************************************
LINEDATA Geosoft binary GDB and Geosoft ASCII XYZ format

***********************************************************
GRIDS, GEOTIFFS, GOOGLE EARTH FILES, VECTORS

File names and general definitions for the raster and vector files are given below. Not all files listed below are included in each format listed above. Grid files are provided in Geosoft binary GRD and ER Mapper ERS formats. Vector files are provided in an ESRI shape file format.

All file names listed below start with 'Idi_'.

 NAME         GENERAL DEFINITION

 mag_diu      Pre-final total magnetic field (without leveling
                and before IGRF removal)
 mag_rmi      Residual magnetic field with IGRF removed (nT)
 magigrf      Total magnetic field with IGRF removed (nT)
 1vd          First vertical derivative (calculated vertical gradient)
                of the total magnetic field with IGRF removed (nT/m)
 asig         Analytic signal calculated from the total magnetic
                field with IGRF removed (nT/m)
 tiltder      Tilt derivative of total magnetic field with
                IGRF removed (degrees)
 res56k       Apparent coplanar resistivity for 56,000 Hz (56 kHz; ohm-m)
 res7200      Apparent coplanar resistivity for 7200 Hz (ohm-m)
 res900       Apparent coplanar resistivity for 900 Hz (ohm-m)
 dtm          Digital terrain or elevation model (m)
 SecGrid      Alaska PLSS Section Grid for map sheets (vector only)
 UTMGrid      NAD27, UTM zone 4N grid (vector only)
 fp           Flight path (vector only)

**********************************************************
MAPS PDF and HPGL/2 formats

The thirteen maps at 1:63,360-scale need three sheets to cover the survey area. Maps are generally produced in two versions, one with data contours and no topography and one with topography and no data contours. Not all images are provided as maps. File 'gpr2011-002_readme.PDF' contains a table linking the map numbers with the data and map version. This information is also in the 'Detailed_Description' section for the maps.

  1. How should this data set be cited?

    Burns, L.E., Fugro Airborne Surveys Corp., and Fugro GeoServices, Inc., 2011, IDITAROD SURVEY AREA: Magnetic and Electromagnetic Line, Grid, and Vector Data and Maps, Innoko, Iditarod, and Ophir mining districts, Iditarod and Ophir quadrangles, western Alaska (DIGHEM [V] SURVEY): Geophysical Report GPR 2011-2, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), Fairbanks, AK, USA.

    Online Links:

    Other_Citation_Details: 1 DVD

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -157.99
    East_Bounding_Coordinate: -156.26
    North_Bounding_Coordinate: 63.17
    South_Bounding_Coordinate: 62.44

  3. What does it look like?

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

    Beginning_Date: Aug-2010
    Ending_Date: Oct-2011
    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: 4
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -159
      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?

    Entity_and_Attribute_Overview:
    The linedata file ('Iditarod') is provided in both Geosoft binary GDB and Geosoft ASCII XYZ formats. A file ('Iditarod_linedata.txt') contains some of the linedata information included in this metadata document, but in normal ASCII text format. Iditarod_linedata.txt is also included with each downloadable zipped database file.

    Each linedata file contains raw and processed linedata, and related calculated fields. Missing data are represented with the dummy variable '*'. Each of the 340 flight lines or partial flight lines (e.g., Line 20210, referred to as 'LINE' attribute) is associated with a 'DATE' (e.g., 2010/09/10), a 'FLIGHT (number)' (e.g., 19056), and a particular multi-record set of data. Each record represents data acquisition from one spatial location in the flight line. A total of 1,952,413 records are present in each data file.

    Entity_and_Attribute_Detail_Citation:
    L.E. Burns, Division of Geological & Geophysical Surveys and Fugro Airborne Surveys
    Iditarod.GDB and Iditarod.XYZ
    The file 'Iditarod' contains raw and processed linedata and related calculated fields for locational, magnetic, and electromagnetic data. The file is provided in Geosoft binary grid (GRD) and Geosoft ASCII XYZ (XYZ) formats; formatting varies slightly between these. 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., 'L20010:19053' and 'T29030:19064'). 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 19066
      //Date 2010/09/12
      Line 29220  (or 'Tie 29220', etc.)
      Followed by all records for points sampled along Line 29220.
         (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 - oriented nominally N20W (340 degrees);
     Tie lines      - oriented nominally N70E (70 degrees); and
     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 SW to
     NE; tie line numbers increase from north to south; 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.
     MAIN LINE NUMBERS:
        Lowest Traverse Lines: L20010 (southwest)
        Highest Traverse Lines: L22770 (northeast)
        Lowest Tie Lines: T29010 (north)
        Highest Tie Lines: T29110 (south)
        Lowest Border Lines: T19120 (increasing in clockwise direction from the southwestern corner)
        Highest Border Lines: T29333 (south)
    ------------------------------------------------------------
     'FLIGHT' DESIGNATORS
     The 5 digit flight designator consists of a two digit Fugro
     Dighem (V) system number (19 for this project) and a three
     digit flight identification number, e.g., '066'.
    

    x_NAD27z4N
    bird position - easting NAD27 (UTM Zone 4N) (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:550652.89
    Maximum:640886.12
    Units:m

    y_NAD27z4N
    bird position - northing NAD27 (UTM Zone 4N) (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:6925776.17
    Maximum:7004543.64
    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: Fugro Airborne Surveys)

    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
    bird position - latitude WGS84 (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:62.4603987
    Maximum:63.1500890
    Units:degrees

    lon_WGS84
    bird position - longitude WGS84 (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-158.0191346
    Maximum:-156.2164147
    Units:degrees

    flight
    First two digits are Fugro's EM bird identification number for the bird used for this job, i.e., '19'. 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. (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:19034
    Maximum:19084
    Units:flight

    date
    dates (yyyy/mm/dd) of production flights (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:2010/08/25
    Maximum:2010/09/16
    Units:day

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

    Range of values
    Minimum:12.63
    Maximum:668.18
    Units:m

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

    Range of values
    Minimum:14.76
    Maximum:283.23
    Units:m

    gpsz
    bird height above geoid. 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: Fugro Airborne Surveys)

    Range of values
    Minimum:147.31
    Maximum:1272.58
    Units:m

    dtm
    digital terrain model (NAD27 UTM zone 4N); calculated from channel 'GPS-Z' and the laser altimeter data (channel 'ALTLAS_BIRD') measured in the bird' (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:56.34
    Maximum:1211.06
    Units:m

    diurnal_filt
    interpolated diurnal ground magnetic intensity; measured every 1.0 sec. (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:55532.77
    Maximum:55610.34
    Units:nT

    diurnal_cor
    diurnal correction - base removed; interpolated from 1.0 second 'diurnal_filt' measurements (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-1839.58
    Maximum:-1762.02
    Units:nT

    mag_raw
    total magnetic field - spike rejected (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:53323.45
    Maximum:57412.78
    Units:nT

    mag_lag
    total magnetic field - corrected for lag (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:53323.45
    Maximum:57412.78
    Units:nT

    mag_diu
    total magnetic field - diurnal variation removed (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:55120.86
    Maximum:59213.62
    Units:nT

    igrf
    international geomagnetic reference field model 2010, updated for date of flight and elevation variations (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:57113.55
    Maximum:57401.87
    Units:nT

    mag_rmi
    residual magnetic intensity (nT) - final; IGRF model 2010, updated for date of flight and elevation variations, was subtracted from Mag_Diu, then the data were leveled. (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-2138.68
    Maximum:1974.11
    Units:nT

    magigrf
    total magnetic field with IGRF removed - final; mag_rmi with constant added back (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:55145.26
    Maximum:59258.05
    Units:nT

    cpi900_FILT
    coplanar inphase 900 Hz - unlevelled (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-42.71
    Maximum:420.50
    Units:ppm

    cpq900_FILT
    coplanar quadrature 900 Hz - unlevelled (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-3.99
    Maximum:381.69
    Units:ppm

    cxi1000_FILT
    coaxial inphase 1000 Hz - unlevelled (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-18.35
    Maximum:97.69
    Units:ppm

    cxq1000_FILT
    coaxial quadrature 1000 Hz - unlevelled (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-12.94
    Maximum:108.06
    Units:ppm

    cxi5500_FILT
    coaxial inphase 5500 Hz - unlevelled (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-9.68
    Maximum:219.23
    Units:ppm

    cxq5500_FILT
    coaxial quadrature 5500 Hz - unlevelled (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-14.57
    Maximum:298.22
    Units:ppm

    cpi7200_FILT
    coplanar inphase 7200 Hz - unlevelled (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-27.12
    Maximum:817.69
    Units:ppm

    cpq7200_FILT
    coplanar quadrature 7200 Hz - unlevelled (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-1.86
    Maximum:1166.28
    Units:ppm

    cpi56K_FILT
    coplanar inphase 56 kHz - unlevelled (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-38.53
    Maximum:2519.90
    Units:ppm

    cpq56K_FILT
    coplanar quadrature 56 kHz - unlevelled (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-6.95
    Maximum:2570.54
    Units:ppm

    cpi900
    coplanar inphase 900 Hz (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-43.27
    Maximum:420.49
    Units:ppm

    cpq900
    coplanar quadrature 900 Hz (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-1.82
    Maximum:381.54
    Units:ppm

    cxi1000
    coaxial inphase 1000 Hz (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-12.07
    Maximum:99.78
    Units:ppm

    cxq1000
    coaxial quadrature 1000 Hz (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-1.15
    Maximum:107.97
    Units:ppm

    cxi5500
    coaxial inphase 5500 Hz (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-7.38
    Maximum:214.95
    Units:ppm

    cxq5500
    coaxial quadrature 5500 Hz (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-2.69
    Maximum:298.20
    Units:ppm

    cpi7200
    coplanar inphase 7200 Hz (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-24.50
    Maximum:817.62
    Units:ppm

    cpq7200
    coplanar quadrature 7200 Hz (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-2.86
    Maximum:1166.29
    Units:ppm

    cpi56k
    coplanar inphase 56 kHz (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-48.52
    Maximum:2519.90
    Units:ppm

    cpq56K
    coplanar quadrature 56 kHz (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-6.85
    Maximum:2570.46
    Units:ppm

    res900
    900 Hz apparent coplanar resistivity; calculated using a pseudo-layer half-space model. (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:0.71
    Maximum:1325.00
    Units:ohm·m

    res7200
    7200 Hz apparent coplanar resistivity; calculated using a pseudo-layer half-space model (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:6.09
    Maximum:10750.00
    Units:ohm·m

    res56K
    56 kHz apparent coplanar resistivity; calculated using a pseudo-layer half-space model (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:9.61
    Maximum:60000.00
    Units:ohm·m

    dep900
    apparent depth 900 Hz (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-99.85
    Maximum:305.23
    Units:m

    dep7200
    apparent depth 7200 Hz (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-94.30
    Maximum:75.69
    Units:m

    dep56K
    apparent depth 56 kHz (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-121.57
    Maximum:28.86
    Units:m

    difi
    difference channel based on cxi5500 & cpi7200 (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-29.81
    Maximum:91.53
    Units:unitless

    difq
    difference channel based on cxq5500 & cpq7200 (Source: Fugro Airborne Surveys)

    Range of values
    Minimum:-31.75
    Maximum:38.32
    Units:unitless

    cppl
    coplanar powerline monitor (Source: Fugro Airborne Surveys)

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

    cxsp
    coaxial spherics monitor (Source: Fugro Airborne Surveys)

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

    cpsp
    coplanar spherics monitor (Source: Fugro Airborne Surveys)

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

    GPR2011-2GridsAsGRD.zip and GPR2011-2GridsAsERM.zip
    The zip files contain the 11 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 4N, and has a 25m cell size with x and y in meters. An image from each of the grids is provided as Geotiffs and KMZ files. Grid files are listed below as attributes.
    
    A Geosoft projection file (GI) is  included for automatic projection of
    each Geosoft grid file when using Oasis Montaj, the Geosoft software.
    Setting the projection can also be done manually in Geosoft without the
    GI file.
    
    
    Each ER Mapper grid consists of two files, a header (projection) 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.
      (Source: Fugro Airborne Surveys)
    

    Idi_MagDiu
    Partially processed total magnetic field (nT); processing included removal of magnetic spikes, correction for lag, and removal of diurnal variations. Not shown as a map. (Source: Fugro Airborne Surveys)

    Grid file

    Idi_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. Shown in map numbers GPR2011-2-1A, 1B, 1C, 2A, 2B, 2C, 7A, 7B, and 7C. (Source: Fugro Airborne Surveys)

    Grid file

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

    Grid file

    Idi_1VD
    First vertical derivative 'dz' (nT/m) of the total magnetic field with IGRF removed; also referred to as 'calculated vertical gradient' (cvg). Shown in map numbers GPR2011-2-3A, 3B, and 3C. (Source: Fugro Airborne Surveys)

    Grid file

    Idi_ASig
    Analytic signal (nT/m) calculated from the total magnetic field with IGRF removed. Shown in map numbers GPR2011-2-4A, 4B, 4C, 5A, 5B, and 5C. (Source: Fugro Airborne Surveys)

    Grid file

    Idi_TiltDer
    Tilt derivative (degrees) of the total magnetic field with IGRF removed. Shown in map numbers GPR2011-2-6A and 6B. Contours from the tilt derivative are shown upon a color shadows residual magnetic field (Idi_MagRMI) in maps GPR2011-2-7A, 7B and 7C. (Source: Fugro Airborne Surveys)

    Grid file

    Idi_Res56k
    Apparent coplanar resistivity (ohm-m) for 56,000 (56k) Hz.; calculated using a pseudo-layer half-space model. Shown in map numbers GPR2011-2-8A, 8B,8C, 9A, 9B, and 9C. (Source: Fugro Airborne Surveys)

    Grid file

    Idi_Res7200
    Apparent coplanar resistivity (ohm-m) for 7200 Hz.; calculated using a pseudo-layer half-space model. Shown in map numbers GPR2011-2-10A, 10B, 10C, 11A, 11B, and 11C. (Source: Fugro Airborne Surveys)

    Grid file

    Idi_Res900
    Apparent coplanar resistivity (ohm-m) for 900 Hz.; calculated using a pseudo-layer half-space model. Shown in map numbers GPR2011-2-12A, 12B, 12C, 13A, 13B, and 13C. (Source: Fugro Airborne Surveys)

    Grid file

    Idi_DTM
    Digital terrain or elevation model (m). Not shown as a map. (Source: Fugro Airborne Surveys)

    Grid file

    Idi_AltLasBird
    EM bird height (m) above surface, measured by Laser altimeter in EM bird. Not shown as a map. (Source: Fugro Airborne Surveys)

    Grid file

    GPR2011-2_GEOTIFFS_NAD27_z4N.zip
    The zip file 'GPR2011-2_TIFS_NAD27_z4N.zip' contains Geotiffs in NAD27, UTM Zone 4N. Each of the 11 grids is represented in Geotiff (TIF) format. The images shown in 7 of the Geotiffs are the same images used on the maps in this publication; no maps were made of the other 4 images. Map numbers are given below for the appropriate Geotiff attribute definition; the correlation between Geotiff image and map number is also given in 'gpr2011_002_readme.pdf'. (Source: Fugro Airborne Surveys)

    Idi_MagDiu
    Partially processed total magnetic field (nT); processing included removal of magnetic spikes, correction for lag, and removal of diurnal variations. Not shown as a map. (Source: Fugro Airborne Surveys)

    Geotiff file

    Idi_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. Shown in map numbers GPR2011-2-1A, 1B, 1C, 2A, 2B, 2C, 7A, 7B, and 7C. (Source: Fugro Airborne Surveys)

    Geotiff file

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

    Geotiff file

    Idi_1VD
    First vertical derivative 'dz' (nT/m) of the total magnetic field with IGRF removed; also referred to as 'calculated vertical gradient' (cvg). Shown in map numbers GPR2011-2-3A, 3B, and 3C. (Source: Fugro Airborne Surveys)

    Geotiff file

    Idi_ASig
    Analytic signal (nT/m) calculated from the total magnetic field with IGRF removed. Shown in map numbers GPR2011-2-4A, 4B, 4C, 5A, 5B, and 5C. (Source: Fugro Airborne Surveys)

    Geotiff file

    Idi_TiltDer
    Tilt derivative (degrees) of the total magnetic field with IGRF removed. Shown in map numbers GPR2011-2-6A and 6B. Contours from the tilt derivative are shown upon a color shadows residual magnetic field (Idi_MagRMI) in maps GPR2011-2-7A, 7B and 7C. (Source: Fugro Airborne Surveys)

    Geotiff file

    Idi_Res56k
    Apparent coplanar resistivity (ohm-m) for 56,000 (56k) Hz.; calculated using a pseudo-layer half-space model. Shown in map numbers GPR2011-2-8A, 8B, 8C, 9A, 9B, and 9C. (Source: Fugro Airborne Surveys)

    Geotiff file

    Idi_Res7200
    Apparent coplanar resistivity (ohm-m) for 7200 Hz.; calculated using a pseudo-layer half-space model. Shown in map numbers GPR2011-2-10A, 10B, 10C, 11A, 11B, and 11C. (Source: Fugro Airborne Surveys)

    Geotiff file

    Idi_Res900
    Apparent coplanar resistivity (ohm-m) for 900 Hz.; calculated using a pseudo-layer half-space model. Shown in map numbers GPR2011-2-12A, 12B, 12C, 13A, 13B, and 13C. (Source: Fugro Airborne Surveys)

    Geotiff file

    Idi_DTM
    Digital terrain or elevation model (m). Not shown as a map. (Source: Fugro Airborne Surveys)

    Geotiff file

    Idi_AltLasBird
    EM bird height (m) above surface, measured by Laser altimeter in EM bird. Not shown as a map. (Source: Fugro Airborne Surveys)

    Geotiff file

    GPR2011-2_KMZS_WGS84.zip
    The zip file 'GPR2011-2KMZS_WGS84.zip' contains Google Earth KMZ files in Geographic Coordinate System (Simple Cylindrical projection) with a WGS84 datum. Each of the 11 grids is included. The images shown in 7 of the KMZ files are the same images used on the maps in this publication; no maps were made of the other 4 images. Map numbers are given below for the appropriate KMZ attribute definition; the correlation between KMZ image and map number is also given in 'gpr2011_002_readme.pdf'. (Source: Fugro Airborne Surveys)

    Idi_MagDiu
    Partially processed total magnetic field (nT); processing included removal of magnetic spikes, correction for lag, and removal of diurnal variations. Not shown as a map. (Source: Fugro Airborne Surveys)

    KMZ file

    Idi_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. Shown in map numbers GPR2011-2-1A, 1B, 1C, 2A, 2B, 2C, 7A, 7B, and 7C. (Source: Fugro Airborne Surveys)

    KMZ file

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

    KMZ file

    Idi_1VD
    First vertical derivative 'dz' ( nT/m) of the total magnetic field with IGRF removed; also referred to as 'calculated vertical gradient' (cvg). Shown in map numbers GPR2011-2-3A, 3B, and 3C. (Source: Fugro Airborne Surveys)

    KMZ file

    Idi_ASig
    Analytic signal (nT/m) calculated from the total magnetic field with IGRF removed. Shown in map numbers GPR2011-2-4A, 4B, 4C, 5A, 5B, and 5C. (Source: Fugro Airborne Surveys)

    KMZ file

    Idi_TiltDer
    Tilt derivative (degrees) of the total magnetic field with IGRF removed. Shown in map numbers GPR2011-2-6A and 6B. Contours from the tilt derivative are shown upon a color shadows residual magnetic field (Idi_MagRMI) in maps GPR2011-2-7A, 7B and 7C. (Source: Fugro Airborne Surveys)

    KMZ file

    Idi_Res56k
    Apparent coplanar resistivity (ohm-m) for 56,000 (56k) Hz.; calculated using a pseudo-layer half-space model. Shown in map numbers GPR2011-2-8A, 8B, 8C, 9A, 9B, and 9C. (Source: Fugro Airborne Surveys)

    KMZ file

    Idi_Res7200
    Apparent coplanar resistivity (ohm-m) for 7200 Hz.; calculated using a pseudo-layer half-space model. Shown in map numbers GPR2011-2-10A, 10B, 10C, 11A, 11B, and 11C. (Source: Fugro Airborne Surveys)

    KMZ file

    Idi_Res900
    Apparent coplanar resistivity (ohm-m) for 900 Hz.; calculated using a pseudo-layer half-space model. Shown in map numbers GPR2011-2-12A, 12B, 12C, 13A, 13B, and 13C. (Source: Fugro Airborne Surveys)

    KMZ file

    Idi_DTM
    Digital terrain or elevation model (m). Not shown as a map. (Source: Fugro Airborne Surveys)

    KMZ file

    Idi_AltLasBird
    EM bird height (m) above surface, measured by Laser altimeter in EM bird. Not shown as a map. (Source: Fugro Airborne Surveys)

    KMZ file

    GPR2011-2_VECTORS.zip
    Data contours produced for the maps are provided in ESRI shape file format. Except for maps GPR2011-2-6 and GPR2011-2-7, the vector files are shown on the maps without topography. Additional vector files included are the flight path, and the Alaska Section Grid and a UTM grid for the map area. (Source: Fugro Airborne Surveys)

    Idi_magRMI_1
    One of four ESRI shape files containing information for the residual magnetic field data contours. This file contains contours for 5 and 10 nT. These lines are the thinnest on the residual magnetic field maps. The 10 nT line is solid, and the 5 nT line is dashed. Shown in map numbers GPR2011-2-1A, 1B, 2A, and 2B. (Source: Fugro Airborne Surveys)

    vector file

    Idi_magRMI_2
    One of four ESRI shape files containing information for the residual magnetic field data contours. This file contains contours for 50 nT. These lines are the middle thickness on the residual magnetic field maps and are solid. Shown in map numbers GPR2011-2-1A, 1B, 2A, and 2B. (Source: Fugro Airborne Surveys)

    vector file

    Idi_magRMI_3
    One of four ESRI shape files containing information for the residual magnetic field data contours. This file contains contours for 250 nT. These lines are the thickest on the residual magnetic field maps and are solid. Shown in map numbers GPR2011-2-1A, 1B, 2A, and 2B. (Source: Fugro Airborne Surveys)

    vector file

    Idi_magRMI_4
    One of four ESRI shape files containing information for the residual magnetic field data contours. This file contains labels for the contours. The labels are made of vector lines, not alphanumeric characters. Shown in map numbers GPR2011-2-1A, 1B, 2A, and 2B. (Source: Fugro Airborne Surveys)

    vector file

    Idi_ASig_1
    One of four ESRI shape files containing information for the analytic signal contours. This file contains contours for 0.1 and 0.2 nT/meter. These lines are the thinnest on the analytic signal maps. The 0.1 nT/meter line is dashed; the 0.2 nT/meter line is solid. Shown in map numbers GPR2011-2-4A, 4B, 4C, 5A, 5B, and 5C. (Source: Fugro Airborne Surveys)

    vector file

    Idi_ASig_2
    One of four ESRI shape files containing information for the analytic signal contours. This file contains contours for 1.0 nT/meter. These lines are the middle thickness on the analytic signal maps and are solid. Shown in map numbers GPR2011-2-4A, 4B, 4C, 5A, 5B, and 5C. (Source: Fugro Airborne Surveys)

    vector file

    Idi_ASig_3
    One of four ESRI shape files containing information for the analytic signal contours. This file contains contours for 5.0 nT/meter. These lines are the thickest on the analytic signal maps and are solid. Shown in map numbers GPR2011-2-4A, 4B, 4C, 5A, 5B, and 5C. (Source: Fugro Airborne Surveys)

    vector file

    Idi_ASig_4
    One of four ESRI shape files containing information for the analytic signal contours. This file contains labels for the contours. The labels are made of vector lines, not alphanumeric characters. Shown in map numbers GPR2011-2-4A, 4B, 4C, 5A, 5B, and 5C. (Source: Fugro Airborne Surveys)

    vector file

    Idi_TILTDER_p45
    One of eight ESRI shape files containing information for the magnetic tilt derivative contours. Two line weights are used in the tilt derivative contours; all are solid. This file contains contours for positive 45 (+45) degrees; the contours are thick and cyan. Tilt derivative contours are shown in map numbers GPR2011-2-6A, 6B, 7A, and 7B. (Source: Fugro Airborne Surveys)

    vector file

    Idi_TiltDer_p30
    One of eight ESRI shape files containing information for the magnetic tilt derivative contours. Two line weights are used in the tilt derivative contours; all are solid. This file contains contours for positive 30 (+30) degrees; the contours are thin and black. Tilt derivative contours are shown in map numbers GPR2011-2-6A, 6B, 7A, and 7B. (Source: Fugro Airborne Surveys)

    vector file

    Idi_TiltDer_p15
    One of eight ESRI shape files containing information for the magnetic tilt derivative contours. Two line weights are used in the tilt derivative contours; all are solid. This file contains contours for positive 15 (+15) degrees; the contours are thin and black. Tilt derivative contours are shown in map numbers GPR2011-2-6A, 6B, 7A, and 7B. (Source: Fugro Airborne Surveys and Laurel Burns)

    vector file

    Idi_TiltDer_0
    One of eight ESRI shape files containing information for the magnetic tilt derivative contours. Two line weights are used in the tilt derivative contours; all are solid. This file contains contours for 0 degrees; the contours are thick and black. Tilt derivative contours are shown in map numbers GPR2011-2-6A, 6B, 7A, and 7B. (Source: Fugro Airborne Surveys and Laurel Burns)

    vector file

    Idi_TiltDer_n15
    One of eight ESRI shape files containing information for the magnetic tilt derivative contours. Two line weights are used in the tilt derivative contours; all are solid. This file contains contours for negative 15 (-15) degrees; the contours are thin and black. Tilt derivative contours are shown in map numbers GPR2011-2-6A, 6B, 7A, and 7B. (Source: Fugro Airborne Surveys)

    vector file

    Idi_TiltDer_n30
    One of eight ESRI shape files containing information for the magnetic tilt derivative contours. Two line weights are used in the tilt derivative contours; all are solid. This file contains contours for negative 30 (-30) degrees; the contours are thin and black. Tilt derivative contours are shown in map numbers GPR2011-2-6A, 6B, 7A, and 7B. (Source: Fugro Airborne Surveys)

    vector file

    Idi_TiltDer_n45
    One of eight ESRI shape files containing information for the magnetic tilt derivative contours. Two line weights are used in the tilt derivative contours; all are solid. This file contains contours for negative 45 (-45) degrees; the contours are thick and red. numbers GPR2011-2-6A, 6B, 7A, and 7B. (Source: Fugro Airborne Surveys)

    vector file

    Idi_TiltDer_Labels
    One of eight ESRI shape files containing information for the magnetic tilt derivative contours. This file contains labels for the contours. The labels are made of vector lines, not alphanumeric characters. Tilt derivative contours are shown in map numbers GPR2011-2-6A, 6B, 7A, and 7B. (Source: Fugro Airborne Surveys)

    vector file

    Idi_Res56k_1
    One of five ESRI shape files containing information for the 56,000 Hz coplanar apparent resistivity contours. The apparent resistivity maps use a logarithmic scale for the contours. This file contains contours for the minor intervals (i.e., 125, 200, 300, 500, 800, 1,250, 2,000, 3,000, 5,000, 8,000, and 12,500 ohm-m) between the decades of 100, 1,000, 10,000, and 100,000. These lines are the thinnest on the 56,000 Hz coplanar apparent resistivity maps and are solid. Shown in map numbers GPR2011-2-8A, 8B, 8C, 9A, 9B, and 9C. (Source: Fugro Airborne Surveys)

    vector file

    Idi_Res56k_2
    One of five ESRI shape files containing information for the 56,000 Hz coplanar apparent resistivity contours. The apparent resistivity maps use a logarithmic scale for the contours. This file contains contours for the major intervals (i.e., 150, 250, 400, 600, 1,500, 2,500, 4,000, 6,000, and 15,000 ohm-m) between the decades of 100, 1,000, 10,000, and 100,000. These lines are the middle thickness on the 56,000 Hz coplanar apparent resistivity maps and are solid. Shown in map numbers GPR2011-2-8A, 8B, 8C, 9A, 9B, and 9C. (Source: Fugro Airborne Surveys)

    vector file

    Idi_Res56k_3
    One of five ESRI shape files containing information for the 56,000 Hz coplanar apparent resistivity contours. The apparent resistivity maps use a logarithmic scale for the contours. This file contains contours for the decades 100, 1,000, and 10,000 ohm-m. These lines are the thickest on the 56,000 Hz coplanar apparent resistivity maps and are solid. Shown in map numbers GPR2011-2-8A, 8B, 8C, 9A, 9B, and 9C. (Source: Fugro Airborne Surveys)

    vector file

    Idi_Res56k_4
    One of five ESRI shape files containing information for the 56,000 Hz coplanar apparent resistivity contours. This file contains labels for the contours. The labels are made of vector lines, not alphanumeric characters. Shown in map numbers GPR2011-2-8A, 8B, 8C, 9A, 9B, and 9C. (Source: Fugro Airborne Surveys)

    vector file

    Idi_Res56k_5
    One of five ESRI shape files containing information for the 56,000 Hz coplanar apparent resistivity contours. This file contains 'triangles' that are used to indicate the lowest contours in an area. The 'triangles' (composed of scribbled infill) are attached to the lowest contour and point in the direction of the low. Shown in map numbers GPR2011-2-8A, 8B, 8C, 9A, 9B, and 9C. (Source: Fugro Airborne Surveys)

    vector file

    Idi_Res7200_1
    One of five ESRI shape files containing information for the 7200 Hz coplanar apparent resistivity contours. The apparent resistivity maps use a logarithmic scale for the contours. This file contains contours for the minor intervals (i.e., 125, 200, 300, 500, 800, 1,250, 2,000, 3,000, 5,000, and 8,000 ohm-m) between the decades of 100, 1,000, and 10,000. These lines are the thinnest on the 7200 Hz coplanar apparent resistivity maps and are solid. Shown in map numbers GPR2011-2-10A, 10B, 10C, 11A, 11B, and 11C. (Source: Fugro Airborne Surveys)

    vector file

    Idi_Res7200_2
    One of five ESRI shape files containing information for the 7200 Hz coplanar apparent resistivity contours. The apparent resistivity maps use a logarithmic scale for the contours. This file contains contours for the major intervals (i.e., 150, 250, 400, 600, 1,500, 2,500, 4,000, and 6,000 ohm-m) between the decades of 100, 1,000, and 10,000. These lines are the middle thickness on the 7200 Hz coplanar apparent resistivity maps and are solid. Shown in map numbers GPR2011-2-10A, 10B, 10C, 11A, 11B, and 11C. (Source: Fugro Airborne Surveys)

    vector file

    Idi_Res7200_3
    One of five ESRI shape files containing information for the 7200 Hz coplanar apparent resistivity contours. The apparent resistivity maps use a logarithmic scale for the contours. This file contains contours for the decades 100, 1,000, and 10,000 ohm-m. These lines are the thickest on the 7200 Hz coplanar apparent resistivity maps and are solid. Shown in map numbers GPR2011-2-10A, 10B, 10C, 11A, 11B, and 11C. (Source: Fugro Airborne Surveys)

    vector file

    Idi_Res7200_4
    One of five ESRI shape files containing information for the 7200 Hz coplanar apparent resistivity contours. This file contains labels for the contours. The labels are made of vector lines, not alphanumeric characters. Shown in map numbers GPR2011-2-10A, 10B, 10C, 11A, 11B, and 11C. (Source: Fugro Airborne Surveys)

    vector file

    Idi_Res7200_5
    One of five ESRI shape files containing information for the 7200 Hz coplanar apparent resistivity contours. This file contains 'triangles' that are used to indicate the lowest contours in an area. The 'triangles' (composed of scribbled infill) are attached to the lowest contour and point in the direction of the low. Shown in map numbers GPR2011-2-10A, 10B, 10C, 11A, 11B, and 11C. (Source: Fugro Airborne Surveys)

    vector file

    Idi_Res900_1
    One of five ESRI shape files containing information for the 900 Hz coplanar apparent resistivity contours. The apparent resistivity maps use a logarithmic scale for the contours. This file contains contours for the minor intervals (i.e., 125, 200, 300, 500, 800, and 1,250 ohm-m) between the decades of 100, 1,000, and 10,000. These lines are the thinnest on the 900 Hz coplanar apparent resistivity maps and are solid. Shown in map numbers GPR2011-2-12A, 12B, 12C, 13A, 13B, and 13C. (Source: Fugro Airborne Surveys)

    vector file

    Idi_Res900_2
    One of five ESRI shape files containing information for the 900 Hz coplanar apparent resistivity contours. The apparent resistivity maps use a logarithmic scale for the contours. This file contains contours for the major intervals (i.e., 150, 250, 400, and 600 ohm-m) between the decades of 100, 1,000, and 10,000. These lines are the middle thickness on the 900 Hz coplanar apparent resistivity maps and are solid. Shown in map numbers GPR2011-2-12A, 12B, 12C, 13A, 13B, and 13C. (Source: Fugro Airborne Surveys)

    vector file

    Idi_Res900_3
    One of five ESRI shape files containing information for the 900 Hz coplanar apparent resistivity contours. The apparent resistivity maps use a logarithmic scale for the contours. This file contains contours for the decades 100 and 1,000 ohm-m. These lines are the thickest on the 900 Hz coplanar apparent resistivity maps and are solid. Shown in map numbers GPR2011-2-12A, 12B, 12C, 13A, 13B, and 13C. (Source: Fugro Airborne Surveys)

    vector file

    Idi_Res900_4
    One of five ESRI shape files containing information for the 900 Hz coplanar apparent resistivity contours. This file contains labels for the contours. The labels are made of vector lines, not alphanumeric characters. Shown in map numbers GPR2011-2-12A, 12B, 12C, 13A, 13B, and 13C. (Source: Fugro Airborne Surveys)

    vector file

    Idi_Res900_5
    One of five ESRI shape files containing information for the 900 Hz coplanar apparent resistivity contours. This file contains 'triangles' that are used to indicate the lowest contours in an area. The 'triangles' (composed of scribbled infill) are attached to the lowest contour and point in the direction of the low. Shown in map numbers GPR2011-2-12A, 12B, 12C, 13A, 13B, and 13C. (Source: Fugro Airborne Surveys)

    vector file

    Idi_FP_1
    One of four ESRI shape files containing information about the flight path. This file contains all flight lines. (Source: Fugro Airborne Surveys)

    vector file containing lines for all flight lines

    Idi_FP_3
    One of four ESRI shape files containing information about the flight path. This file contains tic marks and associated alphanumeric numbers, for fiducial marks (FIDs) ending in '00' and '50' as well as tic marks for beginning and ending FIDs regardless of the FID value. Lyn Vanderstarren of Fugro Airborne surveys manually corrected the placement of the text. (Source: Fugro Airborne Surveys)

    vector file containing lines and numbers for major FIDs and beginning and ending FIDs

    Idi_FP_2
    One of four ESRI shape files containing information about the flight path. This file contains tic marks for fiducial marks (FIDs) ending in '10', '20', '30', '40', '60', '70', '80', and '90'. These fiducial tics are not labeled with any numbers. (Source: Fugro Airborne Surveys)

    vector file containing lines for minor FIDs

    Idi_FP_1001
    One of four ESRI shape files containing information about the flight path. This file contains individual alphanumeric characters that form the line numbers and flight numbers. Between each line number and associated flight number, a '<' or '>' points in the direction of flight. (Source: Fugro Airborne Surveys)

    vector file containing lines for alphanumeric characters

    Idi_SecGrid
    Alaska PLSS Section Grid (original file name 'pls_section') for the map areas. Modified by Fugro Airborne Surveys 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 Fugro Airborne Surveys)

    vector file containing alphanumeric characters

    IDI_UTMGrid
    A UTM grid for the maps areas produced by Fugro Airborne Surveys. Contains non-alphanumeric labels around the edges of the map sheets. (Source: Fugro Airborne Surveys)

    file containing alphanumeric characters

    Entity_and_Attribute_Overview:
    Maps are provided in PDF and HPGL/2 format, and are downloadable in zip files by data format. The HPGL/2 maps are divided into three 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.

    Three map sheets, labeled 'A', 'B' and 'C', are needed to cover the survey area at a scale of 1:63,360 (inch-to-a-mile). Most geophysical images are placed on two maps, one with topography and one with data contours and no topography. Thirteen different maps (39 map sheets) are included in this publication. Bounding coordinates for the sheets are given immediately below.

    ** 'A' maps - northern part of area ******

       West, -157.25
       East, -156.17
       North, 63.17
       South, 62.83
    
    ** 'B' maps - middle part of area *******
       West, -157.33
       East, -156.42
       North, 62.83
       South, 65.50
    
    ** 'C' maps - southwestern part of area *******
       West, -158.08
       East, -157.33
       North, 62.75
       South, 65.42
    
    Authors and titles of the maps are like the example given below:

    Burns, L.E., Fugro Airborne Surveys Corp., and Fugro GeoServices, Inc., 2011, Residual magnetic field of the Iditarod Survey Area, Innoko, Iditarod, and Ophir mining districts, western Alaska, part of Iditarod and Ophir quadrangles: Alaska Division of Geological & Geophysical Surveys Geophysical Report 2011-2-1A, 1 sheet, scale 1:63,360.

       Publication No   Part of Map Title	                                   Includes
       GPR2011-2-1   Residual magnetic field                                  topography
       GPR2011-2-2   Residual magnetic field with data contours
       GPR2011-2-3   First vertical derivative of the magnetic field          topography
       GPR2011-2-4   Analytic Signal                                          topography
       GPR2011-2-5   Analytic Signal  with data contours
       GPR2011-2-6   Magnetic tilt derivative and data contours               topography
       GPR2011-2-7   Color shadow residual magnetic field with magnetic
                     tilt derivative contours                                 topography
       GPR2011-2-8   56K Hz coplanar apparent resistivity                     topography
       GPR2011-2-9   56K Hz coplanar apparent resistivity with data contours
       GPR2011-2-10  7200 Hz coplanar apparent resistivity                    topography
       GPR2011-2-11  7200 Hz coplanar apparent resistivity with data contours
       GPR2011-2-12  900 Hz coplanar apparent resistivity                     topography
       GPR2011-2-13  900 Hz coplanar apparent resistivity with data contours
    
    Entity_and_Attribute_Detail_Citation:
    L.E. Burns, Division of Geological & Geophysical Surveys, and Fugro Airborne Surveys
    GPR2011-2_MapsAsPDFS.zip, GPR2011-2_MapsAsHPGL2_1-5.zip, GPR2011-2_MapsAsHPGL2_6-8.zip, and GPR2011-2_MapsAsHPGL2_9-13.zip
    Zip file names indicate the map numbers and format included in the zip file. (Source: Fugro Airborne Surveys)


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 as part of the DGGS Airborne Geophysical/Geological Mineral Inventory (AGGMI) program.

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

    Alaska Division of Geological & Geophysical Surveys
    Geophysicist
    3354 College Rd
    Fairbanks, AK 99709-3707
    USA

    (907) 451-5020 (voice)


Why was the data set created?

The survey was part of the Alaska Airborne Geophysical/Geological Mineral Inventory project funded by the Alaska State Legislature and managed by State of Alaska, Department of Natural Resources (DNR), Division of Geological & Geophysical Surveys (DGGS). The project seeks to catalyze private-sector mineral development investment. The project delineates mineral zones on Alaska state lands that: 1) have major economic value; 2) can be developed in the short term to provide high quality jobs for Alaska; and 3) will provide economic diversification to help offset the loss of Prudhoe Bay oil revenue.


How was the data set created?

  1. From what previous works were the data drawn?

    Akima, 1970 (source 1 of 2)
    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:
    Fugro Airborne Surveys used a modification of this method while making grids.

    ADNR-LRIS, 1995 (source 2 of 2)
    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://mapper.landrecords.info/> (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 GPR 2011-2. 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 publication date given above reflects the current metadata file for the Alaska PLSS Section Grid.

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

    Date: 2010 (process 1 of 7)
    The airborne geophysical data were acquired with a DIGHEM (V) Electromagnetic (EM) system and a Fugro D1344 cesium magnetometer with a Scintrex CS3 cesium sensor between August 5 to August 24, 2010. The EM and magnetic sensors were flown at a height of 100 feet. 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) along N20W (340 degrees)
    survey flight lines with one-quarter mile (402.3 m) line spacing. Tie
    lines were flown perpendicular to the flight lines at intervals of
    approximately 3 miles (4,828 m). Traverse line coverage was 3,003.8 mi
    (4,834.2 km) and tie line coverage 395.8 mi (637.0 km) for a total of
    3,399.6 km (5,471.2 km) of data. This distance includes overlapping
    reflight segments but not any rejected portions of lines.
    
    
    A Novatel OEM4-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 0.1
    second (10 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 4N)
    spheroid, 1927 North American datum using a central meridian (CM) of 159
     degrees, a north constant of 0, and an east constant of 500,000.
    

    Date: 2010 (process 2 of 7)
    The total magnetic field data were acquired with a sampling interval of 0.1 seconds, and were (1) corrected for measured system lag (resulting in channel 'mag_lag' in file 'Iditarod.gdb'), (2) corrected for diurnal variations by subtraction of the digitally recorded base station magnetic data (resulting in channel 'mag_diu' in file 'Iditarod.gdb'), (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' in file 'Iditarod.gdb'), and (5) increased by a constant IGRF average value to restore the mag_rmi values to a total magnetic field channel (resulting in channel 'magigrf' in 'Iditarod.gdb'). 'Mag_Diu', '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: 2010 (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 (Idi_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 (Idi_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 ('Idi_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 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: 2010 (process 4 of 7)
    The DIGHEM (V) EM system measured inphase and quadrature components at five frequencies. Two vertical coaxial-coil pairs operated at 1113 (1000) and 5491 (5500) Hz while three horizontal coplanar-coil pairs operated at 923 (900), 7090 (7200), and 55,590 (56,000) Hz. 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: 2010 (process 5 of 7)
    The digital elevation/terrain model was produced from the differentially corrected GPS-Z data (channel 'GPSZ' in file 'Iditarod.gdb') and the laser altimeter data measured in the bird (channel 'ALTLAS_BIRD' in file 'Iditarod.gdb'). 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: 2010 (process 6 of 7)
    DGGS downloaded the Alaska PLSS Section Grid shapefile in fall 2010 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: 2011 (process 7 of 7)
    The HPGL/2 files were created with HP Designjet 5000 printer driver v5.32 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., Stevens Exploration Management Corp., and Fugro Airborne Surveys Corp., 2000, DVD containing profile data, gridded data, vector data, and location information of 2000 geophysical survey data for parts of the Aniak and Iditarod mining districts, southwestern Alaska: Geophysical Report GPR 2000-38, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), Fairbanks, AK, USA.

    Online Links:

    Other_Citation_Details: 2 DVDs
    Burns, L.E., U.S. Bureau of Land Management, Surveys, Fugro Airborne , and Stevens Exploration Management Corp., 2003, Line, grid, and vector data of the airborne geophysical survey data of the Sleetmute area, southwestern Alaska: Geophysical Report GPR 2003-10, 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 file 'IDITAROD.GDB' contains 1,954,413 records with 50 channels each. Channel names and definitions of all 50 channels are included in 'Iditarod_linedata.txt' and the 'Entity_and_Attribute_Information' section of this metadata.

    Fifty-three channels were sampled or are based on sampling at 0.1 sec. intervals. Six of the seven channels listed immediately below were sampled at intervals larger than 0.1 sec. and contain interpolated data. The seventh is based on one of the interpolated channels. The first five values in the table below were measured at 0.5 seconds, but the base station was measured at 1.0 seconds, and thus the post-processed value is also good to 1.0 second.

    CHANNELS CONTAINING INTERPOLATED VALUES

    ***************************************
     X_NAD27z4N (location information; interpolated to 0.1 second from 1.0 second post-processed value)
     Y_NAD27z4N (location information; interpolated to 0.1 second from 1.0 second post-processed value))
     GPSZ (height above geoid information; interpolated to 0.1 second from 1.0 second post-processed value)
     lat_WGS84  (location information; interpolated to 0.1 second from 1.0 second post-processed value)
     lon_WGS84  (location information; interpolated to 0.1 second from 1.0 second post-processed value)
     diurnal_filt (diurnal filter; interpolated to 0.1 second from 1.0 second-sampled 'diurnal_filt')
     diurnal_cor (the correction applied based on the interpolated 'diurnal_filt' channel)
    
    Few values are missing from the databases. CHANNELS WITH MISSING VALUES IN 'IDITAROD.GDB' Channel Data Null Values Values
    *****************************************
     cpsp              1,954,399          14
     cxsp              1,954,394          19
     cppl              1,954,372          41
     diurnal_filt      1,954,339          74
     mag_raw           1,952,640       1,773
     mag_lag           1,952,497       1,916
     mag_diu           1,952,497       1,916
     mag_rmi           1,952,497       1,916
     magigrf           1,952,497       1,916
     res56K            1,943,388      11,025
     res7200           1,943,388      11,025
     res900            1,943,388      11,025
     dep56k            1,852,537     101,876
     dep7200           1,832,294     122,119
     dep900            1,743,697     210,716
    
    Missing magnetic values occur in the Iditarod database for the typical reasons of the lagging process, at the beginning of some lines, and due to despiking. The Iditarod data has a number of magnetic dropouts. When the missing interval is too wide to comfortably interpolate, the area is left as dummies in the database. When the profile gaps are extensive enough, the gridding does not spline across them. Two gaps are present in the Iditarod magnetic grids. Missing values in the apparent resistivity (res56k, res7200, and res900) and associated calculated 'depth' (dep56k, dep7200, and dep900) are due to calculations being meaningless, generally caused by increase in altitude.

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

    Data for this survey were collected by a single subcontractor (Fugro Airborne Surveys) who 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 are 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. 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 (DGGS).

  1. Who distributes the data set? (Distributor 1 of 1)

    State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS)
    Natural Resource Technician
    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 above whenever possible.
  2. What's the catalog number I need to order this data set?

    Geophysical Report 2011-2

  3. What legal disclaimers am I supposed to read?

    The State of Alaska makes no express or implied warranties (including warranties of merchantability and fitness) with respect to the character, function, or capabilities of the electronic services 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, any failure thereof, or otherwise, and in no event will the State of Alaska's liability to the requester 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?

    Custom views or processing may be requested. Please contact Laurel Burns by phone (907-451-5021), e-mail (laurel.burns@alaska.gov), or fax (907-451-5050) to discuss custom processing availability, fees, and turnaround time.

  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 website (<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: 13-Oct-2011
Last Reviewed: 13-Oct-2011
To be reviewed: 21-Jun-2014
Metadata author:
State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS)
Geophysicist (Laurel Burns)
3354 College Road
Fairbanks, AK 99709-3707
USA

907-451-5021 (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 contact us through the e-mail address above whenever possible.
Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:


Generated by mp version 2.9.6 on Mon Oct 24 16:08:40 2011