GEOMORPHIC FEATURES OF THE NORTHERN FLORIDA REEF TRACT REVEALED BY NASA EXPERIMENTAL ADVANCED AIRBORNE RESEARCH LIDAR (EAARL) SURVEYS

The NASA Experimental Advanced Airborne Research Lidar (EAARL), a temporal waveform-resolving, airborne green wavelength lidar, is designed to sense the highly resolved submarine topography and morphologic habitat complexity of shallow reef substrates. During a two-week time period in August 2002, EAARL missions staged from Marathon, Florida collected dense submarine topographic measurements over a broad swath of the northern Florida reef tract extending from north of Triumph Reef to south of Carysfort Reef. The NASA - USGS Airborne Lidar Processing System (ALPS) was used to create a one-meter resolution submarine digital elevation model (DEM) for the northern Florida reef tract. The surveyed region is a high-latitude reef system on a Pleistocene carbonate platform covered by carbonate sand, turtle grass, platform-margin and transitional reefs, and numerous scattered patch reefs surrounded by bare sandy halos. Submarine topographic maps derived from the NASA EAARL optical soundings reveal numerous geomorphic features associated with Holocene platform flooding and reef genesis, including relict subaerial sedimentary structures, fluvial channels, and parallel barrier reef trends associated with differing size classes of patch reefs. Pacific Reef and Ajax Reef, outer bank reefs that are among the northernmost members of a discontinuous chain of shelf-margin reefs that extends from the Dry Tortugas to Fowey Rocks just south of Miami, are depicted in fine spatial detail in on the EAARL lidar topographic maps. The lidar survey also documents the lack of ocean-facing spur and groove structure on the seaward flanks of these major bank reefs. A drowned platform-margin barrier reef associated with a deep adjacent swath of densely clustered, relatively small lagoonal patch reefs was revealed by the EAARL survey. More recent features depicted on the lidar maps include the topographic expression of rubble zones and sea grass "blow-outs" along the landward flanks of bank reefs, evidence of the relatively frequent hurricanes that impact the northern Florida Keys.