Greg Desmond 200710 text files, shapefiles http://sofia.usgs.gov/exchange/desmond/desmondelev.html 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 http://sofia.usgs.gov/exchange/desmond/desmondelev.html. 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. 1995 1996 ground condition Complete As needed -80.625 -80.25 25.625 25.375 none High accuracy elevation data mapping digital elevation data DEM ISO 19115 Topic Category elevation 006 Department of Commerce, 1995, Countries, Dependencies, Areas of Special Sovereignty, and Their Principal Administrative Divisions, Federal Information Processing Standard (FIPS) 10-4, Washington, DC, National Institute of Standards and Technology United States US U.S. Department of Commerce, 1987, Codes for the identification of the States, the District of Columbia and the outlying areas of the United States, and associated areas (Federal Information Processing Standard 5-2): Washington, DC, NIST Florida FL Department of Commerce, 1990, Counties and Equivalent Entities of the United States, Its Possessions, and Associated Areas, FIPS 6-3, Washington, DC, National Institute of Standards and Technology Miami-Dade County USGS Geographic Names Information System Goulds Perrine Grossman Hammock Royal Palm Ranger Station none South East Coast none None. Acknowledgement of the U.S. Geological Survey would be appreciated for products derived from these data. Bob Glover U.S. Geological Survey mailing address

521 National Center

Reston VA 20192 USA 703 648-5056 rglover@usgs.gov http://sofia.usgs.gov/exchange/desmond/desmondelev.html USGS High Accuracy Elevation Data GIF http://sofia.usgs.gov/exchange/desmond/atlas/ USGS HAED Electronic Atlas (view data by USGS 24K topographic quads) GIF 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. compressed ESRI shapefile (.zip) and comma-separated value file (.csv) Grossman Hammock and Royal Palm Ranger Station are included in both the helicopter AHF & airboat and truck datasets All verified and accepted data points are included in the files for each area 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. 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 200708 Susan D. Price U.S. Geological Survey mailing address

521 National Center

Reston VA 20192 USA 703 648 6692 sprice@usgs.gov south east coast of Florida Vector Entity point 1925 Universal Transverse Mercator 17 0.9996 -81 0 500000 0 Coordinate Pair 400 400 meters North American Datum of 1983 Geodetic Reference System 80 6378137 298.257 North American Vertical Datum of 1988 .01 meters Explicit elevation coordinate included with horizontal coordinates ELEV_M ground surface elevation in meters USGS X_UTM UTM X coordinate in meters for the data collection point USGS Y_UTM UTM Y coordinate in meters for the data collection point USGS QUAD_NAME The name of the USGS 1:24, 000-scale topographic quadrangle in which the point falls USGS SUR_METHOD type of surveying method - truck USGS Heather S.Henkel U.S. Geological Survey mailing address

600 Fourth St. South

St. Petersburg FL 33701 USA 727 803-8747 ext 3028 727 803-2030 hhenkel@usgs.gov Truck No warrantees are implied or explicit for the data ASCII 1985 .csv comma-separated values for elevations in map area 3 0.08 http://sofia.usgs.gov/exchange/desmond/desmondelev.html Files may be downloaded from the SOFIA website zip unknown shp.zip ArcGIS shapefile and associated files for the elevations collected by truck file must be unzipped before use 0.051 http://sofia.usgs.gov/exchange/desmond/desmondelev.html Data may be downloaded from the SOFIA website none 20071024 Heather Henkel U.S. Geological Survey mailing and physical address

600 Fourth Street South

St. Petersburg FL 33701 USA 727 803-8747 ext 3028 727 803-2030 sofia-metadata@usgs.gov Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998