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Desmond, Greg, 200710, High Accuracy Elevation Data - Water Conservation Areas and Greater Everglades Region.
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.
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)
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.
703 648-5056 (voice)
The data are from 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. 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.
1. Collection of GPS XYZ points in and around the Greater Everglades Region from the Water Conservation Areas (1A, 2A, 2B, 3A, and 3B), Big Cypress National Preserve, the Everglades National Park, to the Florida Bay, and environs using the following collection platforms: 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 50,000 data records were aggregated and reformatted using custom shell scripts. These data were imported into ArcGIS (version 9.1) to create the the shapefile HAED_v01.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:
703 648 6692 (voice)
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).
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.
All verified and accepted data points are included in the files for the area
The Grossman Hammock and Perrine quadrangles have helicopter AHF & airboat and truck data
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.
727 803-8747 ext 3028 (voice)
727 803-2030 (FAX)
helicopter & airboat
No warrantees are implied or explicit for the data
|Data format:||comma-separated values for the elevations in map area 2 in format ASCII (version 1985) csv Size: 4.5|
|Data format:||comma-separated values for elevations in map area 2 in format zip (version unknown) csv.zip Size: 0.7|
|Data format:||ArcGIS shapefiles and associated files for map area 2 in format zip (version unknown) shp.zip Size: 1.7|
727 803-8747 ext 3028 (voice)
727 803-2030 (FAX)
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