Great Sand Dunes, Colorado

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Frequently anticipated questions:


What does this data set describe?

Title: Great Sand Dunes, Colorado
Abstract:
Aeromagnetic data were collected along flight lines by instruments in an aircraft that recorded magnetic-field values and locations. This dataset presents latitude, longitude, altitude, and magnetic-field values.
  1. How might this data set be cited?
    U.S. Geological Survey, Department of Interior and the National Geophysical Data Center, NOAA, 2012, Great Sand Dunes, Colorado.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -105.68
    East_Bounding_Coordinate: -105.49
    North_Bounding_Coordinate: 37.85
    South_Bounding_Coordinate: 37.52
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 06-Oct-2008
    Ending_Date: 25-Oct-2008
    Currentness_Reference:
    Time period indicates dates of airborne survey data collection. Time period is expressed in the format YYYYMM or YYYYMMDD when further accuracy is available.
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: tabular 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?
  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: 4322 Project name: Great Sand Dunes, Colorado Survey flown by: Upper Limit Aviation Survey flown for: U.S. Geological Survey Approx. no. of line miles: 2267 Survey height: 330 ft Altitude method: Draped over terrain Flight-line spacing: 0.09 mi Flight-line direction: E-W Aircraft used: Bell 206 B3 helicopter Airport - arrival: Alamosa, CO Airport - departure: Alamosa, CO Stinger length: unknown Magnetometer used: Scintrex CS-3 Cesium Data recording interval: 0.1 second Regional field removed: IGRF 2005
    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, Department of Interior and the National Geophysical Data Center, NOAA
  2. Who also contributed to the data set?
    These USGS employees contributed to reformatting and archiving these data: Bob Kucks, Pat Hill
  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: 2008 (process 1 of 2)
    Conversion of measured values to geographic position and magnetic values was performed by the contractor using industry standard practices.
    Date: Aug-2009 (process 2 of 2)
    USGS personnel used the software package Oasis Montaj by Geosoft, Inc., to read in the original contractor's data. Few, if any, corrections were made to the original data. Minor changes may have been made to the original format. A readme.txt file was created to outline the format of the .xyz file.
  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 data in this file have been processed using various formulas and methods that are not usually documented but that represent industry standard practices for airborne data reduction. See operations report for discussion on data acquisition and processing.
  2. How accurate are the geographic locations?
    Horizontal positions of the survey aircraft used to collect data were determined using GPS satellite navigation.
  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. Radar altimeters are estimated to have an error of 2-5% of the altitude (Richard Hansen, PRJ, Inc., written communication).
    Barometric altimeters are quite accurate, but are typically operated in an uncorrected mode. The diurnal variation in air pressure over the course of a flight can produce a 50-100 ft error in the barometric altimeter reading. In addition, pressure microcells create short- period air pressure changes equivalent to about 10 ft. under typical conditions (Richard Hansen, PRJ, Inc., written communication) This data set was collected as a draped survey having an average terrain clearance of 330 ft. Because aircraft cannot safely maintain a constant terrain clearance, error in vertical position is introduced.
  4. Where are the gaps in the data? What is missing?
    Loss of data due to poor transmission, channel dropout, obvious spiking, missing channels, and other obvious errors may have been replaced with the value -9999.9.
  5. How consistent are the relationships among the observations, including topology?
    The data in this file 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 contracts 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 and the National Geophysical Data Center would be appreciated in products derived from these data.
  1. Who distributes the data set? (Distributor 1 of 1)
    Web site administration: U.S Geological Survey Publishing Service Center
    Publishing Service Center
    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 web site 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 (version unknown) See the project readme.txt file for the data format.
      Network links: http://crustal.usgs.gov/geophysics/index.html for link to report
    • Cost to order the data: none


Who wrote the metadata?

Dates:
Last modified: 31-Oct-2011
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:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)

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