Robert Glover, Greg Desmond, Gordon Shupe (retired), Ed Cyran (retired). Charles Henkle (retired)
The inital gage survey was funded by the NMD High Accuracy Elevation Data Collection project. These gage sites were collected informally by NMD personnel as part of the High Accuracy Elevation Data project in the mid to late 1990s, as requested by the scientists. A very comprehensive set of gage sites, descriptions, and values was assembled. Project personnel decided to make a gazetteer for the South Florida community. Therefore, it was not formally reviewed at that time but many scientists have been using it for years. The quality control process was very tight. Sites were usually surveyed several different times. Some gages were re-verified between 2000 and 2007 funded by the Priority Ecosystem Science program. Additionally, the data were processed using different techniques and software packages by several different people.
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).
In most cases the gage recorder housing, or gage box, was used as the monument of the survey measurement. Construction of permanent monuments 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. In most cases benchmarks were installed by Florida coastal staff including outside staff gages.
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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U.S. Department of the Interior, U.S. Geological Survey
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