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Specific deep edge measurements were conducted at ten general areas in the four major bay segments. Seagrass species investigated were: H. wrightii, T. testudinum, and S. filiforme. Most study areas were located at, or close to, an established Tampa Bay fixed seagrass transect and included different seagrass species when present. Further, the depth profile of 20 of the 62 seagrass transects included in the annual interagency seagrass transect monitoring program have been surveyed to this date. These profiles start at the shoreline and extend across the shallow sandbar to approximately the 2m depth contour.
Prior to conducting the elevation measurements at seagrass areas and transects, suitable bench marks had to be located within 10km of the survey sites. NOS tidal bench marks were the primary type used.
Typical set-ups of the GPS instruments for field elevation measurements are shown below. The base station antenna was placed vertically above the bench mark and the rover station antenna was placed, either on a tripod vertically above the seagrass edge (static technique), or as shown here for transect profiling, on a pole attached to a benthic sled (Aon-the-fly” technique). Recorded GPS satellite data was post-processed using the Trimble phase processor software. The software calculated the relative elevation difference between the two antennas (D). Since the MTL elevation of the bench mark (B) was known and the antenna heights (A and C) had been measured in the field, the MTL elevation of the survey site (X) could easily be calculated.
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