Airborne geophysical survey: Berwick '55

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Frequently anticipated questions:


What does this data set describe?

Title: Airborne geophysical survey: Berwick '55
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, 2014, Airborne geophysical survey: Berwick '55.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -71.000671386719
    East_Bounding_Coordinate: -70.747886657715
    North_Bounding_Coordinate: 43.495971679688
    South_Bounding_Coordinate: 43.256313323975
  3. What does it look like?
    http://mrdata.usgs.gov/geophysics/surveys/geophysics3/NH-ME/nh-me0213.jpg (JPEG)
    Reduced-size image depicting the data, 1118 x 1249 pixels, 125,009 bytes
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: Sep-1955
    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?
      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 6378206.4.
      The flattening of the ellipsoid used is 1/294.98.
  7. How does the data set describe geographic features?
    Entity_and_Attribute_Overview:
    Generally these data files contain columnar text consisting of a longitude, latitude, and magnetic anomaly value in nanoTeslas. Where the data files have more columns the package should include a text file explaining the additional columns; that arrangement applies to data recorded originally in digital format, and includes some of the intermediate measurements and calculated parameters such as the total magnetic field.
    Entity_and_Attribute_Detail_Citation: http://pubs.usgs.gov/of/1999/ofr-99-0557/readme.htm

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?
    paper (source 1 of 2)
    Bromery, Randolph Wilson, Zandle, G.L., 1956, Aeromagnetic map of the Alton quadrangle, New Hampshire; Total intensity relative to arbitrary datum: Geophysical Investigation Map 136.

    Online Links:

    Type_of_Source_Media: paper
    Source_Contribution:
    Contours of magnetic anomaly and, where available, flight lines were digitized from this source
    paper (source 2 of 2)
    Bromery, Randolph Wilson, Zandle, G.L., 1956, Aeromagnetic map of Berwick quadrangle, Maine and New Hampshire; Total intensity relative to arbitrary datum: Geophysical Investigation Map 137.

    Online Links:

    Type_of_Source_Media: paper
    Source_Contribution:
    Contours of magnetic anomaly and, where available, flight lines were digitized from this source
  2. How were the data generated, processed, and modified?
    Date: Sep-1955 (process 1 of 2)
    Aeromagnetic survey flown by USGS in the time period 09/55 direction E-W at altitude 750 AG with spacing 0.5 mi. for a total of 800 line miles
    Date: 2000 (process 2 of 2)
    USGS digitized original paper map to ASCII format points. 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?

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

  1. How well have the observations been checked?
    Because these data were digitized from printed contour maps that were drawn originally by researchers who produced the source materials, the values presented here should be regarded as approximate and faithful to the published interpretation (contouring) of the original instrument data. Factors affecting accuracy include the accuracy and precision of the original aircraft flight line navigation and elevation as well as the calibration of the instruments used to measure the magnetic field.
  2. How accurate are the geographic locations?
    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?
    Contouring, and subsequently digitizing of the contours, covered areas that included original flight line data, so these data may not extend into all parts of the original map extents.
  5. How consistent are the relationships among the observations, including topology?
    In general each original map shows data collected by a single contractor or group responsible for collecting and processing the field observations, and reflect industry standard practices and controls as of the time period when the maps were published. 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? nh-me0213.txt
  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: 05-Dec-2014
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)

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