Gamma-ray, Magnetic, and Topographic Data for the Colorado Front Range

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Frequently anticipated questions:


What does this data set describe?

Title:
Gamma-ray, Magnetic, and Topographic Data for the Colorado Front Range
Abstract:
The grid files presented here are in ASCII format that uses the definitions of the grid exchange format (GXF). The files can be viewed using a suitable word processing program. The different grids are:
Kfrco.gxf    potassium concentrations in the rocks and soils
Ufrco.gxf    uranium concentrations in the rocks and soils
Thfrco.gxf   thorium concentrations in the rocks and soils
Magfrco.gxf  residual magnetic field
Terrfrco.gxf digital elevations
The data used to create the potassium (K), uranium (U), thorium (Th), and magnetic (Mag) grids were obtained as part of the National Uranium Resource Evaluation (NURE) Program of the U.S. Department of Energy (USDOE). The NURE Program included aerial surveys that collected gamma-ray and magnetic data. The aerial surveys were flown at a nominal altitude of 122 meters above the ground. The aerial survey flightlines were generally flown east- west with north-south tielines. For the data covering the mountains of the Colorado Front Range, the flightline spacing is 1 mile (1600 meters) for the east-west lines and about 8 miles (12.8 km) for the north-south tielines. For the data covering the plains to the east of the mountains, the flightline spacing is 3 miles (4800 m) for the east-west lines and about 16 miles (25.6 km) for the north-south tielines. In the mountains, helicopters were used with a detector volume of 2000 cubic inches (32.8 liters) of thallium doped sodium iodide (NaI(Tl)). Over the plains, fixed-wing aircraft were used with about 3300 cubic inches (54 liters) of NaI(Tl) detector. The magnetometers used were proton-precession magnetometers with base stations used to make diurnal corrections. The USDOE contracted with private contractors to conduct the aerial surveys and the contractors were responsible for all aspects of calibration and data processing.
The data used to create the grid of digital elevations were derived from the U.S. Geological Survey (USGS) 1:250,000 topographic quadrangle maps. The topographic maps were digitized at intervals of three arc-seconds and were then averaged to intervals of 15 seconds. The resulting 15-second data were used to calculate the grid presented here.
The units of the grid data are:
Potassium     percent K
Uranium       parts per million (ppm) eU
Thorium       ppm eTh
Magnetic      nano Teslas
Elevation     meters
  1. How might this data set be cited?
    Duval, Joseph S., Reed, John C., and Zietz, Isadore, 2000, Gamma-ray, Magnetic, and Topographic Data for the Colorado Front Range: USGS Open-File Report 2000-331, U.S. Geological Survey, Reston, Virginia.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -106
    East_Bounding_Coordinate: -105
    North_Bounding_Coordinate: 36
    South_Bounding_Coordinate: 32
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 1978
    Ending_Date: 1979
    Currentness_Reference:
    publication date
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: raster digital data
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      Indirect_Spatial_Reference: The data are located strictly by the coordinates.
      This is a Raster data set. It contains the following raster data types:
      • Dimensions 539 x 181 x 1, type Grid Cell
    2. What coordinate system is used to represent geographic features?
      The map projection used is Transverse Mercator.
      Projection parameters:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -105
      Latitude_of_Projection_Origin: 0
      False_Easting: 0
      False_Northing: 0
      Planar coordinates are encoded using Row and Column
      Abscissae (x-coordinates) are specified to the nearest 0.635
      Ordinates (y-coordinates) are specified to the nearest 0.635
      Planar coordinates are specified in kilometers
      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 6378.2064.
      The flattening of the ellipsoid used is 1/294.98.
  7. How does the data set describe geographic features?

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Duval, Joseph S.
    • Reed, John C.
    • Zietz, Isadore
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?

Why was the data set created?

These data were originally obtained to aid in the estimate of uranium resources in the United States.

How was the data set created?

  1. From what previous works were the data drawn?
    USDOE, GJBX-17-79 (source 1 of 2)
    Geometrics, Inc., 1979, Aerial gamma ray and magnetic survey; Rock Springs, Rawlins, and Cheyenne quadrangles, Wyoming and the Greeley Quadrangle, Colorado: Open-File Report GJBX-17-79, U.S. Department of Energy, Grand Junction, CO.

    Other_Citation_Details: 5 volumes
    Type_of_Source_Media: paper
    Source_Contribution:
    These publications describe the aerial surveys, how they were flown, and data processing steps.
    USDOE, GJBX-49-79 (source 2 of 2)
    Geometrics, Inc., 1979, Aerial gamma ray and magnetic survey; Rockies/Laramie Range Project; Denver and Pueblo quadrangles, Colorado: Open-File Report GJBX-49-79, U.S. Department of Energy, Grand Junction, CO.

    Other_Citation_Details: 4 volumes
    Type_of_Source_Media: paper
    Source_Contribution:
    This report describes the aerial survey, how it was flown, and data processing steps.
  2. How were the data generated, processed, and modified?
    Date: 1997 (process 1 of 1)
    The flightline data were read from tape and were converted to grids using USGS gridding programs. Person who carried out this activity:
    Joseph S. Duval
    U.S. Geological Survey
    Geophysicist
    12201 Sunrise Valley Drive
    Mail Stop 954
    Reston, VA
    USA

    (703) 648-6106 (voice)
    (703) 648-6383 (FAX)
    jduval@usgs.gov
    Contact_Instructions: email preferred
    Data sources used in this process:
    • USDOE, GJBX-17-79 and GJBX-49-79
  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?
    The absolute accuracy of the concentrations of potassium, uranium, and thorium are estimated to be on the order of 20-30 percent. The accuracy of the magnetic data is about 2 nT. Because of the manner in which the elevation data have been averaged, the values should only be used in a qualitative manner.
  2. How accurate are the geographic locations?
    The position of the aircraft during the aerial surveys was constantly monitored.
  3. How accurate are the heights or depths?
    The position of the aircraft during the aerial surveys was constantly monitored.
  4. Where are the gaps in the data? What is missing?
    All of the available flightline data were used. Because of differences in the calibrations of the data sets, scaling adjustments were made to correct scaling differences. The following publication provides detailed information on the corrections made:
    Duval, J.S. and Riggle, F.E., 1999, Profiles of gamma-ray and magnetic data from aerial surveys over the conterminous United States: U.S. Geological Survey Digital Data Series DDS-31, Release 2, 3 CD-ROMs.
  5. How consistent are the relationships among the observations, including topology?
    The concentration data are based upon calibrations done using the airport calibration pads in Grand Junction, Colorado and the dynamic test strip at Lake Mead, Nevada.

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)
    USGS ESIC-Open-File Report Sales
    Mail Stop 517
    U.S. Geological Survey
    Box 25286, Building 810
    Denver Federal Center
    Denver, CO
    USA

    (303) 202-4210 (voice)
    (303) 236-4031 (FAX)
  2. What's the catalog number I need to order this data set? USGS Open-File Report 2000-331
  3. What legal disclaimers am I supposed to read?
    This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards (or with the North American Stratigraphic Code). Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 23-Feb-2015
Metadata author:
Peter N. Schweitzer
U.S. Geological Survey
Collection manager, USGS Geoscience Data Clearinghouse, http://geo-nsdi.er.usgs.gov/
12201 Sunrise Valley Drive
Mail Stop 954
Reston, VA
USA

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

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