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High Accuracy Elevation Data - Lake Okeechobee Littoral Zone

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Frequently-anticipated questions:

What does this data set describe?

Title: High Accuracy Elevation Data - Lake Okeechobee Littoral Zone
The U.S. Geological Survey (USGS) coordinated the acquisition of high accuracy elevation data (meters) for the Lake Okeechobee Littoral Zone collected on a 400 meter topographic grid with a vertical accuracy of +/- 15 centimeters. The elevations are referenced to the horizontal North American Datum of 1983 (NAD83) and vertical North American Vertical Datum of 1988 (NAVD88). The topographic surveys were performed using differential GPS technology and a USGS developed helicopter-based instrument known as the Airborne Height Finder (AHF).

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, 2007, High Accuracy Elevation Data - Lake Okeechobee Littoral Zone: U.S. Geological Survey, Reston, VA.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -81.25
    East_Bounding_Coordinate: -80.625
    North_Bounding_Coordinate: 27.25
    South_Bounding_Coordinate: 26.625

  3. What does it look like?

    <https://sofia.usgs.gov/exchange/desmond/atlas/> (GIF)
    map of USGS topographic quads containing elevation data around Lake Okeechobee
    <https://sofia.usgs.gov/exchange/desmond/desmondelev.html> (GIF)
    map showing the location of high accuracy elevation data around Lake Okeechobee

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

    Beginning_Date: 24-Jul-2006
    Ending_Date: 12-Oct-2006
    Currentness_Reference: ground condition

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

    Geospatial_Data_Presentation_Form: text files, shapefile

  6. How does the data set represent geographic features?

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

      Indirect_Spatial_Reference: South Florida - Lake Okeechobee Littoral Zone
      This is a Vector data set. It contains the following vector data types (SDTS terminology):
      • Entity point (2865)

    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)

    The vegetation observed by the surveyor at the data collection point. Vegetation types include Alligator Hole, Broadleaf Emergent, Cattail, Cypress, Floating Emergent, Hardwood, Lygodium, Melaleuca, Open Water, Palmetto, Pine, Sawgrass, Shrub, Slough, Tree Island, Wet Prairie, Wet Prairie/Slough, and Willow Shrub (Source: USGS)

    type of surveying method - all data for the Lake Littoral zone were collected using the helicopter based Airborne Height Finder (AHF) (Source: USGS)

    Characters 1-5 are the file name used by the surveyor during data collection. Characters 6-8 are the Julian date of the data collection. Characters 9-10 are the year the data were collected. Character 11 is a blank space. Characters 12-19 represent the date the data were released for publication and archive after the data have been collected, processed, edited, quality controlled, and approved for release. Character 20 is "Y" which means the data can be released. This is not the date the data were collected.

    If new data were added to the quadrangle, the revision date was modified for ALL points in the quadrangle to reflect the latest revision date. At the completion of data collection, the individual quad-based files were aggregated to create the larger files now available for download. (Source: USGS)

    file name used by the surveyor for internal data management purposes (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?

    GPS data converted to ESRI shapefile by Susan D. Price. Data collection done by Charles Henkle and Ed Cyran as USGS contractors.

  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?

This project performed regional topographic surveys to collect and provide elevation data to parameterize hydrologic and ecological numerical simulation models that are being developed for ecosystem restoration activities.

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) are being 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 consists of the following steps:

    1.Collection of GPS XYZ points and vegetation classification in the Lake Okeechobee Littoral Zone using the helicopter-based Airborne Height Finder (AHF) developed by the USGS.

    2. The GPS data were processed into an ASCII list of NAD83 geographic XY coordinates, NAVD88 elevation Z value and descriptor attribute data. This file was transformed using Corpscon, version 5.11.08 from the U.S. Army Corps of Engineers to NAD83 UTM XY and NAVD88 Z coordinates. The file was output as an ASCII text file and processed at USGS in Reston, VA.

    3. The x,y, and z values of the ASCII text file were reformatted to the decimal value of 100th of meter (centimeter) to represent the accuracy of the data and then imported into ArcGIS 9.1 to create an ESRI shapefile.

    4. The ESRI shapefile was compressed into a .zip file using WinZip. The associated .dbf files were 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?

    not available

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?

    Helicopter - Airborne Height Finder

  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_okee.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 14:49:41 2007