Bathymetry of Biscayne National Park

Patterson, Judd

Mosaiced submerged bathymetry raster for the marines areas of Biscayne National Park. This raster image combines two original data sources to create a merged bathymetry layer for the submerged areas of Biscayne National Park. The original layers and their details are: 1) NOAA Estuarine Bathymetry - Bathymetry for Biscayne Bay was derived from twelve surveys containing 149,227 soundings. The overlap from three older, less accurate surveys was omitted before tinning the data. The twelve surveys used dated from 1930 to 1993. Approximately 60 percent of the surveys were from 1934. Surveys from 1980 to 1993 cover the eastern portion of the bay. The total range of sounding data was 0.6 meters to -10.4 meters at mean low water. Mean high water values between 0.1 and 0.6 meters were assigned to the shoreline. Fourteen points were found that were not consistent with the surrounding data. These were removed prior to tinning. Biscayne Bay has fifteen 7.5 minute DEMs and a single one degree DEM. Bathymetric elevations within these data sets are referenced to the local tidal datum which typically is Mean Lowest Low Water (MLLW) averaged over a 19 year tidal epoch. Elevations above this datum (between the datum and the shoreline) have positive values (meters to centimeter resolution) while those below are negative. 2) NPS/FWC LIDAR - Blom Aerofilms won a contrat from The Florida Fish and Wildlife Institute for the acquisition of bathymetric LiDAR services on the East coast of Florida approximately 22km south east of Miami airport in Biscayne National Park. The aerial acquisition of the laser data was successfully completed on 11th December 2008 using the Hawk Eye Mk II airborne Bathymetric LiDAR System after a 7 day capture programme of the survey area. The depths to be achieved from the survey were expected to be between 0 and 30m which came from assessment of green laser wavelength data using SeaWIFS at the time of tender. The elevations in this file were in the NAVD88 vertical datum. In areas of overlap, the NPS/FWC LIDAR was used because it is newer and more accurate. Since the offshore LIDAR used NAVD88 and the inshore bathymetry used MLLW, a correction factor was also needed to balance elevations across the final map. This correction factor was estimated by looking at the seam between the two layers and was approximately 2 meters. The Raster Calculator tool was used to subtract 2 meters from the inshore bathymetry file before merging with the offshore LIDAR. While this final product approximates park wide coverage in NAVD88, it should be noted that inside the bay is a little less accurate because an actual vertical datum conversion was not performed.