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High Accuracy Elevation Data - truck

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Frequently-anticipated questions:

What does this data set describe?

Title: High Accuracy Elevation Data - truck
The High Accuracy Elevation Data Project collected elevation data (meters) on a 400 meter topographic grid with a vertical accuracy of +/- 15 centimeters to define the topography in South Florida. The data are referenced to the horizontal datum North American Datum 1983 (NAD 83) and the vertical datum North American Vertical Datum 1988 (NAVD 88). The High Accuracy Elevation Data Project began with a pilot study in FY 1995 to determine if the then state-of-the-art GPS technology could be used to perform a topographic survey that would meet the vertical accuracy requirements of the hydrologic modeling community. The initial testing platform was from a truck and met the accuracy requirements. Data were collected in areas near Homestead, Florida. The data are available for the areas shown on the USGS High Accuracy Elevation Data graphic at <https://sofia.usgs.gov/exchange/desmond/desmondelev.html>.
  1. How should this data set be cited?

    Desmond, Greg, 200710, High Accuracy Elevation Data - truck.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -80.625
    East_Bounding_Coordinate: -80.25
    North_Bounding_Coordinate: 25.625
    South_Bounding_Coordinate: 25.375

  3. What does it look like?

    <https://sofia.usgs.gov/exchange/desmond/desmondelev.html> (GIF)
    USGS High Accuracy Elevation Data
    <https://sofia.usgs.gov/exchange/desmond/atlas/> (GIF)
    USGS HAED Electronic Atlas (view data by USGS 24K topographic quads)

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date: 1995
    Ending_Date: 1996
    Currentness_Reference: ground condition

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: text files, shapefiles

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      Indirect_Spatial_Reference: south east coast of Florida
      This is a Vector data set. It contains the following vector data types (SDTS terminology):
      • Entity point (1925)

    2. What coordinate system is used to represent geographic features?

      Grid_Coordinate_System_Name: Universal Transverse Mercator
      UTM_Zone_Number: 17
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -81
      Latitude_of_Projection_Origin: 0
      False_Easting: 500000
      False_Northing: 0

      Planar coordinates are encoded using Coordinate Pair
      Abscissae (x-coordinates) are specified to the nearest 400
      Ordinates (y-coordinates) are specified to the nearest 400
      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.
      The flattening of the ellipsoid used is 1/298.257.

      Altitude_Datum_Name: North American Vertical Datum of 1988
      Altitude_Resolution: .01
      Altitude_Distance_Units: meters
      Explicit elevation coordinate included with horizontal coordinates

  7. How does the data set describe geographic features?

    ground surface elevation in meters (Source: USGS)

    UTM X coordinate in meters for the data collection point (Source: USGS)

    UTM Y coordinate in meters for the data collection point (Source: USGS)

    The name of the USGS 1:24, 000-scale topographic quadrangle in which the point falls (Source: USGS)

    type of surveying method - truck (Source: USGS)

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

    • Greg Desmond

  2. Who also contributed to the data set?

    Data collection done by Charles Henkle, Gordon Shupe, Bob Glover, Ed Cyran, and Greg Desmond of the USGS and contractors. Other project personnel include Vince Caruso, Gary Freeman, and Susan Price.

  3. To whom should users address questions about the data?

    Bob Glover
    U.S. Geological Survey
    521 National Center
    Reston, VA 20192

    703 648-5056 (voice)

Why was the data set created?

These data are from topographic surveys to collect and provide elevation data to parameterize hydrologic and ecological numerical simulation models that were being developed for ecosystem restoration activities. Surveying services were also rendered to provide vertical reference points for numerous water level gauges.

Modeling of sheet flow and water surface levels in the wetlands of South Florida is very sensitive to changes in elevation due to the expansive and extremely low relief terrain. Hydrologists have determined minimum vertical accuracy requirements for the elevation data for use as input to hydrologic models. As a result, elevation data with a vertical accuracy specification of +/-15 centimeters (cm) relative to the North American Vertical Datum of 1988 (NAVD88) were collected in critical areas using state-of-the-art differential global positioning system (GPS) technology and data processing techniques.

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: Aug-2007 (process 1 of 1)
    The process for creating digital elevation files consisted of the following steps:

    1. Collection of GPS XYZ points in map area 3 during the pilot study started in FY 1995.

    2. The GPS data were transformed from NAD83 geographic X, Y coordinates and NAVD88 elevation Z valuse to NAD83 UTM X, Y and NAVD88 Z coordinates via "Corpscon for Windows" from the U.S. Army Corps of Engineers. <http://crunch.tec.army.mil/software/corpscon/corpscon.html>

    3. The coordinate data were imported into a geographic information system to create multiple geospatial data formats.

    4. The ascii text file containing 1925 data records was aggregated and reformatted using custom shell scripts.

    5. The shapefile-associated .dbf file was opened in MS Excel and saved as the comma-separated value file which also is available for download

    Person who carried out this activity:

    Susan D. Price
    U.S. Geological Survey
    521 National Center
    Reston, VA 20192

    703 648 6692 (voice)

  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?

  2. How accurate are the geographic locations?

    Horizontal positions are established by GPS observations and are referenced to the North American Datum of 1983 (NAD83). The desired horizontal accuracy is +/- 15 centimeters. This level of accuracy is consistent with GPS differential techniques which use two stations - a high-quality dual-frequency GPS receiver base station and a roving GPS station. The density and accuracy of a given GPS data observation varies from a few meters to a few centimeters according to the Position Dilution of Precision (PDOP) in the study area. Generally if the PDOP is observed to be excessive, data collection is discontinued or the data are discarded. The PDOP is an indicator of the positional accuracy of the GPS that be can derived from the current GPS satellite geometry, which varies continuously. Generally the smaller the PDOP number, the higher the data quality. The PDOP is a permanent part of the recorded data and is also included in the post processing procedures during reduction of the GPS observations to NAD 83. Where possible, the GPS base station has an ellipsoid height to an accuracy of two centimeters relative to the Continuously Operating Reference Stations (CORS) or the High Accuracy Reference Network (HARN), both operated by the National Geodetic Survey (NGS).

  3. How accurate are the heights or depths?

    For all elevation data the vertical accuracy specification is +/- 15 centimeters and is referenced to NAVD 1988.

    This elevation data is intended primarily for use in hydrological modeling. It is collected as high accuracy, "bare earth" ground elevation. That is, the data are restricted to ground elevations only. "Bare earth" in the Everglades swamp environment is generally considered to be the layer of "muck" which will support a one pound weight on a bearing surface of approximately 5.3 square inches (2.6 inch circle). In non-swamp areas it is actual bare ground.

  4. Where are the gaps in the data? What is missing?

    All verified and accepted data points are included in the files for each area

  5. How consistent are the relationships among the observations, including topology?

    Grossman Hammock and Royal Palm Ranger Station are included in both the helicopter AHF & airboat and truck datasets

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints: none
None. Acknowledgement of the U.S. Geological Survey would be appreciated for products derived from these data.

  1. Who distributes the data set? (Distributor 1 of 1)

    Heather S.Henkel
    U.S. Geological Survey
    600 Fourth St. South
    St. Petersburg, FL 33701

    727 803-8747 ext 3028 (voice)
    727 803-2030 (FAX)

  2. What's the catalog number I need to order this data set?


  3. What legal disclaimers am I supposed to read?

    No warrantees are implied or explicit for the data

  4. How can I download or order the data?

Who wrote the metadata?

Last modified: 24-Oct-2007
Metadata author:
Heather Henkel
U.S. Geological Survey
600 Fourth Street South
St. Petersburg, FL 33701

727 803-8747 ext 3028 (voice)
727 803-2030 (FAX)

Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

This page is <https://sofia.usgs.gov/metadata/sflwww/HAED_truck.faq.html>

U.S. Department of the Interior, U.S. Geological Survey
Comments and suggestions? Contact: Heather Henkel - Webmaster
Generated by mp version 2.8.18 on Wed Oct 24 14:54:29 2007