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Everglades Gage Gazetteer


Methodology

Included here, is an excerpt of the Everglades Gage Gazetteer. This compilation contains the results of geodetic surveys at Everglades water gage sites by personnel of the U. S. Geological Survey (USGS) Eastern Region Geography, formerly the National Mapping Division (NMD). These surveys were conducted under the auspices of the USGS Place-Based Studies Program, and the Everglades National Park Critical Ecosystem Studies Initiative. The data also includes results from the 1997 Florida Bay Marine Monitoring Network Gage Survey, a cooperative effort between the USGS and the U.S. Army Corps of Engineers. Altogether, surveys have been completed at fifty National Park Service, sixty-three USGS/WRD, twenty-two USGS/BRD, 2 Big Cypress National Preserve, and 2 Florida Atlantic University sites. The Gazetteer couples positional and descriptive data with a photographic record of each site. It is our hope that this format will facilitate positive identification of the sites and their associated geodetic reference points.

In most cases the gage recorder housing, or gage box, was used as the monument of the survey measurement. Construction of more permanent monumentation was beyond the mission and manpower of the survey project. Nonetheless the gage box serves as a fairly stable and readily identifiable temporary monument. Gage operators are encouraged to transfer the height of the surveyed reference point from the gage box to permanent locations, especially before modifying the gage structure.

The survey data presented here were established with differential GPS techniques which provide three-dimensional (3D) measurements. The 3D position measured at each point is provided as latitude, longitude and ellipsoid height in the NAD 83 datum. The reported NAVD 88 elevation, in meters, is the National Geodetic Survey (NGS) GEOID99 modeled orthometric height.

Although all the sites were positioned with GPS, this compilation includes results of different GPS methods and survey procedures, yielding small but significant differences in vertical accuracy. One hundred-nine sites were positioned by static occupations, and thirty-six by the USGS Airborne Height Finder (AHF) System. The AHF surveys, with repeat observations at each site, provide heights within 4-5 cm of datum. A majority of the static surveys employed long duration observations, typically 48 hours, producing heights within 2 cm of datum. The 1997 Florida Bay Survey is estimated to be within 3-4 cm of datum, due to different procedures and the available reference control.

Beginning in 1998, both the AHF and the static gage surveys were tied to ground stations of the AHF Control Network, developed by USGS and referenced to NAD 83(97) via the NGS MIA3 Continuously Operating Reference Station (CORS). This common reference frame allows both survey methods to achieve a level of datum consistency previously unattainable in the Everglades region. For the first time in this harsh and geodetically challenging environment, the geospatial relationship of even the most remote monitoring sites has been reliably determined.



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Last updated: 15 Jan, 2013 @ 12:42 PM (KP)