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High Accuracy Elevation Data Collection Project

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Frequently-anticipated questions:

What does this data set describe?

Title: High Accuracy Elevation Data Collection Project
Abstract:
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. In some areas, the surveying was accomplished using airboats. Because access was a logistical problem with airboats, the USGS developed a helicopter-based instrument known as the Airborne Height Finder (AHF). All subsequent data collection used the AHF.

Data were collected from the Loxahatchee National Wildlife Refuge, south through the Water Conservation Areas (1A, 2A, 2B, 3A, and 3B), Big Cypress National Park, the Everglades National Park, to the Florida Bay. Data were also collected in the Lake Okeechobee littoral zone. The data are available for the areas shown on the USGS High Accuracy Elevation Data graphic at <http://sofia.usgs.gov/exchange/desmond/desmondelev.html>. The work was performed for Everglades ecosystem restoration purposes. The project started in 1995 and concluded in 2007.

  1. How should this data set be cited?

    Desmond, Greg, 200710, High Accuracy Elevation Data Collection Project.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -81.625
    East_Bounding_Coordinate: -80.125
    North_Bounding_Coordinate: 27.33
    South_Bounding_Coordinate: 25

  3. What does it look like?

    <http://sofia.usgs.gov/exchange/desmond/desmondelev.html> (GIF)
    map showing areas of USGS High Accuracy Elevation Data collection
    <http://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: 2007
    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 Florida
      This is a Vector data set. It contains the following vector data types (SDTS terminology):
      • Entity point (62185)

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

      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 17
      Transverse_Mercator:
      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.

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

  7. How does the data set describe geographic features?

    ELEV_M
    ground surface elevation in meters (Source: USGS)

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

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

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

    VEG_FS
    The vegetation observed by the surveyor at the data collection point - collection started in 2003 art the request of scientists. 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)

    SUR_METHOD
    type of surveying method (Source: USGS)

    AHF
    Airborne Height Finder - a helicopter-based instrument used to access data points (Source: USGS)

    AHF

    AIRBOAT
    data collected using an airboat to access the data points (Source: USGS)

    AIRBOAT

    TRUCK
    data collected using a truck to access the data points (Source: USGS)

    TRUCK

    SUR_INFO
    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.

    During the 12 year lifetime of the project, data points were released as individual files (see SUR_FILE attribute) to match the published USGS 7.5-minute topographic quadrangle footprint. 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)

    SUR_FILE
    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)

  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
    USA

    703 648-5056 (voice)
    rglover@usgs.gov

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 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 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 and around the Greater Everglades Region from the Loxahatchee National Wildlife Refuge, south through the Water Conservation Areas (1A, 2A, 2B, 3A, and 3B), Big Cypress National Preserve, the Everglades National Park, to the Florida Bay, and Lake Okeechobee Littoral Zone, and environs using multiple collection platforms: truck, airboat and helicopter-based Airborne Height Finder (AHF) developed by the USGS.

    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. Multiple formats of the data were posted to the SOFIA website.

    5. This process was repeated for each quad-based file of data collected by the surveyors during the 12 year life of the project.

    6. The ASCII text files containing more than 62,000 data records were aggregated and reformatted using custom shell scripts. These data were imported into ArcGIS (version 9.1) to create the three shapefiles (Okee_v06.shp, HAED_v01.shp, Truck_v14.shp) available for download.

    7. The associated .dbf files were opened in MS Excel and saved as the comma-separated values files which also are available for download.

    Person who carried out this activity:

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

    703 648 6692 (voice)
    sprice@usgs.gov

  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
Use_Constraints:
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
    USA

    727 803-8747 ext 3028 (voice)
    727 803-2030 (FAX)
    hhenkel@usgs.gov

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

    Elevation Data

  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?

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

727 803-8747 ext 3028 (voice)
727 803-2030 (FAX)
sofia-metadata@usgs.gov

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

This page is <http://sofia.usgs.gov/metadata/sflwww/hi_accuracy_elev_collection_04.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 18:51:03 2007