Airborne geophysical survey: Southwest Virginia

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Frequently anticipated questions:


What does this data set describe?

Title: Airborne geophysical survey: Southwest Virginia
Abstract:
Aeromagnetic data were collected along flight lines by instruments in an aircraft that recorded magnetic-field values and locations. In the earlier days of surveying, the only way to represent this data was to generate an analog map with contour lines. This dataset is a representation of the digitized contour lines either by following the lines or by choosing the intersection of the contour and flight-line to create a value of the magnetic field. The values presented are latitude, longitude, and map magnetic-field values.
  1. How might this data set be cited?
    U.S. Geological Survey and the Department of Interior, 2012, Airborne geophysical survey: Southwest Virginia.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -83.65
    East_Bounding_Coordinate: -80.94
    North_Bounding_Coordinate: 37.54
    South_Bounding_Coordinate: 36.59
  3. What does it look like?
    http://mrdata.usgs.gov/geophysics/surveys/geophysics3/VA/va_va04.jpg (JPEG)
    Reduced-size image depicting the data, 1118 x 721 pixels, 105,885 bytes
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: Feb-1962
    Ending_Date: Apr-1962
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: analog contour map
  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.
    2. What coordinate system is used to represent geographic features?
      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.0001. Longitudes are given to the nearest 0.0001. Latitude and longitude values are specified in decimal degrees. 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 6,378,206.4.
      The flattening of the ellipsoid used is 1/294.98.
  7. How does the data set describe geographic features?
    Entity_and_Attribute_Overview:
    Airborne survey specifications These items are constant for the entire survey Project number: VA04 Project name: Southwest Virginia Survey flown by: Aero Service, Corp. Survey flown for: Virginia Division of Natural Resources Approx. no. of line miles: 3000 Survey height: 5000 ft Altitude method: Above sea level Flight-line spacing: 1.5 mi Flight-line direction: NW-SE Aircraft used: unknown Airport - arrival: unknown Airport - departure: unknown Sensor tow distance: unknown Magnetometer used: unknown Data recording interval: unknown Regional field removed: unknown
    Entity_and_Attribute_Detail_Citation:
    Nettleton, L.L., 1971, Elementary Gravity and Magnetics for Geologists and Seismologists: Society of Exploration Geophysicists Monograph Series No. 1. Dobrin, M.B., 1976, Introduction to Geophysical Prospecting: New York, McGraw-Hill Book Company, Sheriff, R.E., 1984, Encyclopedic dictionary of exploration geophysics: Tulsa, OK, Society of Exploration Geophysicists.

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 and the Department of Interior
  2. Who also contributed to the data set?
    These USGS employees contributed to reformatting and archiving these data: Viki Bankey, Pat Hill, Holly Hindle, Bob Kucks, Sarah Shearer, Esther Castellanous
  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: 1962 (process 1 of 2)
    Conversion of measured values to geographic position and magnetic values was performed by the processors using industry standard practices. Details are found under Horizontal_Position_Accuracy_Report, and Vertical_Position_Accuracy_Report Unless noted, conversion processes were not documented. Products may include some written documentation.
    Date: 2008 (process 2 of 2)
    USGS digitized original map to ASCII format. USGS personnel used the software package Oasis Montaj by Geosoft, Inc., to read in the ASCII digitized data and create raster JPEG images.
  3. What similar or related data should the user be aware of?
    Virginia Division of Natural Resources, 1962, Composite aeromagnetic map of southwestern Virginia: Virginia Division of Natural Resources Map Area H, Virginia Division of Natural Resources, Charlottesville, Virginia.

    Other_Citation_Details: scale 1:250,000

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

  1. How well have the observations been checked?
    The data shown on the original map have been processed using various formulas and methods that are not usually documented but that represent industry standard practices for airborne data reduction. For example, position is listed as latitude and longitude, but these values were derived from the raw navigation data depending on the system used. (see notes under horizontal accuracy). Line numbers were added to records, and unusable data at flight-line ends were discarded (as aircraft slowed and turned around). Separate recordings were correlated by time and assigned to the correct location. The exact accuracies of these processing steps may not be known. They are discussed in the sections on attribute or positional accuracies.
  2. How accurate are the geographic locations?
    Flight Path Recovery Horizontal position of the survey aircraft used to collect data were determined by reconciling down-looking photographs (recorded on continuous-strip film) with topographic maps and orthophotoquadrangle maps. Fiducial numbers and marks, impressed on any paper strips that were recording data or added to magnetic tape records, were included as a function of time to further reconcile location with instrumentation.
  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?
    Data is complete as reasonably digitized from the original map
  5. How consistent are the relationships among the observations, including topology?
    The data on the original map were collected by a single contractor or group who were responsible for collecting and processing the data. The data from this survey were collected using the same instruments (magnetometers, altimeters, navigational systems) throughout the survey and were collected in a normal length of time with no long delays between survey beginning and end. Survey layout specified the conditions and specifications under which these data were collected. Standard industry practices of the time were followed in data collection and processing.

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. Acknowledgement of the U.S. Geological Survey would be appreciated in products derived from these data.
  1. Who distributes the data set? (Distributor 1 of 2)
    Web site administration: U.S Geological Survey Central Publications Group
    Central Publications Group
    USGS MS 902, Box 25046 DFC
    Denver, CO

    303-236-5486 (voice)
  2. What's the catalog number I need to order this data set?
  3. What legal disclaimers am I supposed to read?
    Although all data published on this website have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials. 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?
    • Availability in digital form:
      Data format: ASCII Each line contains data in the following format, beginning with line 1 (no header included): longitude F12.4 Longitude in decimal degrees latitude F12.4 Latitude in decimal degrees mag F8.1 Magnetic value represented on map. This is probably the total field value with an arbitrary datum removed
      Network links: http://crustal.usgs.gov/geophysics/index.html for link to report
    • Cost to order the data: none


  1. Who distributes the data set? (Distributor 2 of 2)
    Peter N Schweitzer
    USGS Eastern Mineral and Environmental Resources Science Center
    Geologist
    12201 Sunrise Valley Drive
    Reston, VA
    USA

    703-648-6533 (voice)
    703-648-6252 (FAX)
    pschweitzer@usgs.gov
  2. What's the catalog number I need to order this data set? va_va04_meta.txt
  3. What legal disclaimers am I supposed to read?
    This dataset was prepared by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed in this report, or represents that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. Any views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 05-Dec-2014
Metadata author:
USGS Crustal Geophysics and Geochemistry Science Center
Magnetic and Gravity Information
U.S. Geological Survey
Box 25046 Mail Stop 964
Denver Federal Center
Denver, CO

303-236-5652 (voice)
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

This page is <https://mrdata.usgs.gov/geophysics/surveys/waf/VA_VA04_META.faq.html>
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