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.
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.
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.
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
U.S. Department of the Interior, U.S. Geological Survey
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