High-Resolution Multibeam Survey of ONR Mine Burial and Scour Study Area near Clearwater, Florida

During April 17-21, 2002, a Kongsberg Simrad EM 3000 (300 kHz) shallow water multibeam bathymetry and backscatter system was used on the R/V Suncoaster to map a series of NW-SE trending sedimentary bedforms which overlie the Florida carbonate platform. The total area covered is approximately nine square nautical miles or 31 square km. The depth ranges from about 10 to 17 meters. Bathymetry and backscatter data characterize a complicated (and unexpected) three-dimensional pattern of sediments and karst-like bathymetry, including vertical (1-3 m) limestone ledges (corroborated by SCUBA dive observations). The mosaic displays two large sedimentary ridges and two very broad troughs that have very little sediment cover composed primarily of shell hash or exposed limestone. Circular-shaped depressions in the trough areas, however, appear to act as traps for finer sediments with the same backscatter characteristics of the large sedimentary ridges. The trough areas also have irregular geomorphology, including several lineaments (km's in length) of unknown origin. The length of the northernmost ridge is at least 4 km. The width of the ridge is sharply defined in the bathymetry data (3-5 m steep relief) and is narrow (about 1 km). A narrow band of low backscatter also suggests a similar width of the ridge, but extends out further N, NW, and W into deeper areas surrounding the ridge. In contrast, the southernmost ridge, is a broader and less sharply defined ridge (1-3 m gradual relief) with a length and width of about 3 and 1.5 km. Furthermore, the backscatter data define the ridge area more sharply than the bathymetry data. This southernmost ridge has been selected for the mine burial and scour experiment in January-March 2003, due to its sediment thickness and geomorphology. Enlarged views of post-processed bathymetry and backscatter will be presented as a poster and interactively using the Fledermaus fly-through software. We will also present preliminary results from automated seafloor bottom classification schemes using the Konsgberg Simrad Triton multibeam software and Quester Tangent single-beam classification (QTC).