Desmond, Greg, 2003, High Accuracy Elevation Data: U.S. Geological Survey, Reston, VA.Online Links:
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.
GPS data converted to DEM's and ARC/INFO coverages by Vince Caruso. Data collection done by Charles Henkel, Gordon Shupe, Bob Glover, Ed Cyran, and Greg Desmond of the USGS and contractors.
703 648 4728 (voice)
703 648 4165 (FAX)
gdesmond@usgs.gov
This project is performing 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 are also being 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) are being 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 Everglades swamp and environs using the helicopter-based Airborne Height Finder (AHF) developed by the USGS. Additional elevation data were acquired through contracted professional surveying services.
2. The GPS data is processed into an ASCII list of coordinates in column order of Point number and/or descriptor attribute data (maximum of 20 characters), NAD83 geographic XY coordinates, and NAVD88 elevation Z value. This file is transformed through NADCON (a conversion program available from the National Geodetic Survey, NGS) to NAD83 UTM XY and NAVD88 Z coordinates. The file is output as an ASCII text file and transferred on-site Reston, VA to a file server/ mass storage device.
3. The coordinates are then processed into an ARC INFO POINT COVER format. An annotation file is created and appended to the POINT cover file for the tabular elevation value of meters to the decimal value of 100th of meter (centimeter). This annotation value is later used to create the illustrated large area point plot file in GEO TIFF format.
4. The POINT cover is then transformed to other final distribution formats.
a. The POINT cover is exported into ARC/INFO Exchange Format (.e00) and transferred to a file server/mass storage device.
b. The POINT cover is used as input to ARC TOPOGRID to create the ARC GRID elevation file.
c. The ARC GRID cover is then used as input to ARC GRIDPAINT in combination with a color ramp and color map file to create the illustrated pseudo-color elevation plot.
Person who carried out this activity:
703 648 4586 (voice)
703 648 4614 (FAX)
vcaruso@usgs.gov
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 following data sets have missing files:
Goulds missing .e00 file Homestead missing .cor file Pennsuco missing .cor file Perrine missing .asc file
The remianing data sets all have .asc, .cor, and .e00 files.
not available
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.
305 717-5824 (voice)
305 717-5801 (FAX)
sunshine@usgs.gov
High accuracy elevation data
No warrantees are implied or explicit for the data
| Data format: | export-formatted interchange file in ASCII for input into ARC/INFO and ArcView in format ARCE (version 7.0) .e00 Size: 1 |
|---|---|
| Network links: |
<http://sofia.usgs.gov/exchange/desmond/desmondelev.html> |
| Data format: | comma delimited complete list of Global Positioning System (GPS) points in format ASCII .asc Size: 0.1 |
|---|---|
| Network links: |
<http://sofia.usgs.gov/exchange/desmond/desmondelev.html> |
| Data format: | complete list of GPS points reformatted to process into ARC/INFO in format ASCII .cor Size: 0.2 |
|---|---|
| Network links: |
<http://sofia.usgs.gov/exchange/desmond/desmondelev.html> |
703 648-4592 (voice)
703 648-4614 (FAX)
jastapleton@usgs.gov
U.S. Department of the Interior, U.S. Geological Survey, Center for
Coastal Geology
Comments and suggestions? Contact: Heather
Henkel - Webmaster
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