Airborne geophysical survey: Firth HEM data

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Frequently anticipated questions:

What does this data set describe?

Title: Airborne geophysical survey: Firth HEM data
This report is a digital data release for a helicopter electromagnetic and magnetic survey that was conducted during March 2007 in three 93-square-kilometer (36-square-mile) areas of eastern Nebraska as part of a joint State of Nebraska and U.S. Geological Survey study. The objective of the survey is to improve the understanding of the relationship between surface-water and ground-water systems critical to developing water resource management programs. The electromagnetic equipment consisted of six different coil-pair orientations that measured electrical resistivity at separate frequencies from about 400 hertz to about 115,000 hertz. The electromagnetic data were converted to electrical resistivity geo-referenced grids and maps, each representing different approximate depths of investigation for each area. The range of subsurface investigation is comparable to the depth of shallow aquifers. The three areas selected for the study, Ashland, Firth, and Oakland, have glacial terrains and bedrock that typify different hydrogeologic settings for surface water and ground water in eastern Nebraska. The geophysical and hydrologic information from U.S. Geological Survey studies are being used by resource managers to develop ground-water resource plans for the area.
  1. How might this data set be cited?
    Smith, B.D., Cannia, J.C., 2008, Airborne geophysical survey: Firth HEM data: U.S. Geological Survey Open-File Report 2008-1018.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -96.63775
    East_Bounding_Coordinate: -96.55325
    North_Bounding_Coordinate: 40.63125
    South_Bounding_Coordinate: 40.59575
  3. What does it look like? (JPEG)
    Reduced-size image depicting the data, 446 x 683 pixels, 144,394 bytes
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 2008
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: vector and raster digital data
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Vector data set. It contains the following vector data types (SDTS terminology):
      • String
    2. What coordinate system is used to represent geographic features?
      The map projection used is Transverse Mercator.
      Projection parameters:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -99.000000
      Latitude_of_Projection_Origin: 0.000000
      False_Easting: 500000.000000
      False_Northing: 0.000000
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 1.49693125
      Ordinates (y-coordinates) are specified to the nearest 1.49693125
      Planar coordinates are specified in meters
      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257222.
  7. How does the data set describe geographic features?
    bounding area of airborne survey maps (Source: U.S. Geological Survey)
    Internal feature number. (Source: ESRI) Sequential unique whole numbers that are automatically generated.
    Feature geometry. (Source: ESRI) Coordinates defining the features.
    Unique ID from DXF polyline (Source: U.S. Geological Survey)
    xxfString of values and text representing the flight path line

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Smith, B.D., Cannia, J.C.
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    Bruce D. Smith
    U.S. Geological Survey
    PO Box 25046,MS973
    Denver, CO

    303.236.1399 (voice)
    Contact_Instructions: Contact via email

Why was the data set created?

Improve the understanding of the relationship between surface-water and ground-water systems critical to developing water resource management programs.

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: 26-Mar-2007 (process 1 of 2)
    Airborne geophysical data processing described in OFR 2008-1018
    Date: 10-Nov-2020 (process 2 of 2)
    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)
  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?
    Arc feature attribute values were inspected and found to be consistently coded as described in the Entity and Attribute section.
  2. How accurate are the geographic locations?
    Horizontal accuracy was not assessed.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    This data set includes only the study area for the HEM investigation conducted near Firth, Nebraska.
  5. How consistent are the relationships among the observations, including topology?
    Using ArcGIS tools and routines all arcs were checked for node errors, overshoots, undershoots, dangles, intersections, and duplicate features.

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
    Water Webserver Team
    12201 Sunrise Valley Drive, MS 440
    Reston, VA

    1-888-475-8747 (1-888-ASK-USGS) (voice)
    Contact_Instructions: Contact via email
  2. What's the catalog number I need to order this data set? Downloadable Data
  3. What legal disclaimers am I supposed to read?
    Although these data have been used by the U.S. Geological Survey, U.S. Department of the Interior, no warranty expressed or implied is made by the U.S. Geological Survey as to the accuracy of the data. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of this data, software, or related materials.
  4. How can I download or order the data?

Who wrote the metadata?

Last modified: 10-Nov-2020
Metadata author:
U.S. Geological Survey
5231 S 19th Street
Lincoln, NE

402.328.4100 (voice)
Contact_Instructions: Contact via email
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

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