Airborne geophysical survey: Taylor Mountains

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Frequently anticipated questions:


What does this data set describe?

Title: Airborne geophysical survey: Taylor Mountains
Abstract:
Aeromagnetic data were collected along flight lines by instruments in an aircraft that recorded magnetic-field intensity values and location. In surveys such as this one where the data were originally collected in digital form and not digitized from contour maps, the information we provide typically includes latitude, longitude, magnetic anomaly in nanoTeslas, and intermediate values used to derive the magnetic anomaly such as total magnetic field.
  1. How might this data set be cited?
    U.S. Geological Survey, 2004, Airborne geophysical survey: Taylor Mountains:.

    Online Links:

    This is part of the following larger work.

    Saltus, R.W., and Milicevic, B., 2004, Preliminary grid data and maps for an aeromagnetic survey of the Taylor mountains quadrangle and a portion of the Bethel quadrangle, Alaska: Open-File Report 2004-1293, U.S. Geological Survey, Reston, VA.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -159.9595
    East_Bounding_Coordinate: -155.8911
    North_Bounding_Coordinate: 61.04317
    South_Bounding_Coordinate: 59.95178
  3. What does it look like?
    http://mrdata.usgs.gov/geophysics/surveys/geophysics2/AK/AK_4292.jpg (JPEG)
    Reduced-size image depicting the data, 3096 x 1656 pixels, 739,844 bytes
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: Apr-2004
    Ending_Date: May-2004
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Point data set. It contains the following vector data types (SDTS terminology):
      • Entity point
    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: 0.0
      False_Easting: 500000
      False_Northing: 0.0
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 1
      Ordinates (y-coordinates) are specified to the nearest 2
      Planar coordinates are specified in meters
      The horizontal datum used is World Geodetic System 1984.
      The ellipsoid used is WGS 84.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257.
  7. How does the data set describe geographic features?
    TaylorMountains.XYZ
    Data file contained within the package AK_4292.ZIP (Source: USGS)
    XUTM84
    Flight-line X coordinate, UTM zone 4, WGS84, meters (Source: Geosoft database)
    ValueDefinition
    *Missing value
    Range of values
    Minimum:116475
    Maximum:342071
    Units:meters
    YUTM84
    Flight-line Y coordinate, UTM zone 4, WGS84, meters (Source: Geosoft database)
    ValueDefinition
    *Missing value
    Range of values
    Minimum:6654459
    Maximum:6778505
    Units:meters
    mag1_mic_fin_305
    Magnetic anomaly in nanoTeslas, with field and lab corrections (Source: Geosoft database)
    ValueDefinition
    *Missing value
    Range of values
    Minimum:-659.51
    Maximum:5829.16
    Units:nanoTeslas

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • U.S. Geological Survey
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?

Why was the data set created?

Aeromagnetic surveys are used for geophysical prospecting. Some variations in magnetic measurements are caused by rocks that contain significant amounts of magnetic minerals (magnetite being the most common). These anomalies reflect variations in the amount and type of magnetic material and the shape and depth of the body of rock. The features and patterns of aeromagnetic anomalies can also be used to delineate details of subsurface geology including the locations of buried faults and the thickness of surficial sedimentary rocks.

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: May-2004 (process 1 of 3)
    The Taylor Mountains aeromagnetic survey was flown in April and May 2004 by McPhar Geosurveys Ltd. under contract to the USGS. The flight lines are oriented northwest to southeast with an interline spacing of 1,600 meters (1 mile). Tie lines were flown in a perpendicular direction (northeast to southwest) with spacing of 12,900 meters (8 miles). The survey flights were 2USGS Open-File Report 20041293 Taylor Mountains, Alaska, preliminary aeromagnetics draped over topography using a preplanned flight surface with a nominal clearance of 305 meters (1,000 feet). Care was taken to avoid data collection during periods of intense diurnal disturbance of the Earths magnetic field. Differential Global Positioning System (GPS) was used for flight navigation.
    Date: 2004 (process 2 of 3)
    This data grid is based on minimum curvature gridding of preliminary flight-line data. Data processing at this stage includes field corrections and office corrections. In the field: (1) Compensation for the airplane magnetic field, (2) heading correction (for the influence of the direction in which the magnetic sensor is traversing the Earths magnetic field), (3) lag correction (compensation for the difference of position between the GPS and magnetic sensors). In the office: (4) Tie-line leveling, (5) International Geomagnetic Reference Field (IGRF) removal using IGRF 2000, and (6) microleveling to remove residual flight-line artifacts. Note that base station magnetic data were recorded at several field sites but have not yet been processed or applied to the preliminary data grid. The data have not been subjected to contractor or USGS quality-control checks. The data appear consistent with previous aeromagnetic data and grids for this region (Saltus and Simmons, 1997). The grid is projected using the WGS 84 datum and Universal Transverse Mercator Zone 4. The X location of the bottom-left grid data point is 447,300 meters. The Y location of the bottomleft grid data point is 6,647,200 meters. There are 635 columns (west to east) and 346 rows (south to north) in the data grid. Each grid cell is 350 meters on a side. Person who carried out this activity:
    U.S. Geological Survey, Mineral Resources Program
    Attn: Richard W. Saltus
    Mail Stop 964 Building 20 Denver Federal Center, West 6th Avenue and Kipling Streets
    Lakewood, Colorado

    303-236-1375 (voice)
    303-236-1425 (FAX)
    saltus@usgs.gov
    Date: 10-Nov-2020 (process 3 of 3)
    Added keywords section with USGS persistent identifier as theme keyword. Person who carried out this activity:
    U.S. Geological Survey
    Attn: VeeAnn A. Cross
    Marine Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2251 (voice)
    508-457-2310 (FAX)
    vatnipp@usgs.gov
  3. What similar or related data should the user be aware of?

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

  1. How well have the observations been checked?
    A preliminary data grid has a grid cell size of 350 meters (1150 feet). Final data processing and quality control have not been applied to these data. The purpose of this preliminary data release is to allow prompt public access to these data, which are of interest for active mineral exploration in the region. A more complete data release and description will be published later once the final data processing is complete.
  2. How accurate are the geographic locations?
    Detailed positional information is determined by the contractor using navigational controls to specifications given in the contractor reports. Generally these are more precise and accurate for newer surveys than for older ones.
  3. How accurate are the heights or depths?
    The aircraft vertical position was determined using the navigational positioning equipment on the aircraft, which were radar altimeter and barometric altimeter.
  4. Where are the gaps in the data? What is missing?
    of 4,857,396 flight-line points, 11,025 contain missing values, each represented by an asterisk
  5. How consistent are the relationships among the observations, including topology?
    In general each original survey was collected by a single contractor, who would be responsible for processing the field observations, and reflect industry standard practices and controls. Variation among surveys is possible, especially if they were carried out during very different time periods.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: none
Use_Constraints: none
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey, Mineral Resources Program
    Attn: Peter N. Schweitzer
    Mail Stop 954 USGS National Center, 12201 Sunrise Valley Drive
    Reston, Virginia

    703-648-6533 (voice)
    703-648-6252 (FAX)
    pschweitzer@usgs.gov
  2. What's the catalog number I need to order this data set? AK_4292.zip
  3. What legal disclaimers am I supposed to read?
    Reference herein to any specific commercial product, process, or service by trade name,trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 10-Nov-2020
Metadata author:
U.S. Geological Survey, Mineral Resources Program
Attn: Peter N. Schweitzer
Mail Stop 954 USGS National Center, 12201 Sunrise Valley Drive
Reston, Virginia

703-648-6533 (voice)
703-648-6252 (FAX)
pschweitzer@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

This page is <https://mrdata.usgs.gov/geophysics/surveys/waf/AK_4292_META.faq.html>
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