APPLICATION OF UNDERWATER LASER SCANNING FOR SEAFLOOR SHELL FRAGMENTS CHARACTERIZATION

Two features required for modeling high-frequency acoustic scattering from seafloor are roughness and discrete objects distributed on the seafloor. A laser scanner was deployed to acquire fine-scale bottom roughness off the coast of New Jersey in 2006. On the bathymetry map, it was found that the sites were covered by shell fragments. Cross-comparison between the laser reflection intensity and the bathymetry suggests that the shell fragments have a stronger reflection intensity than the seafloor. This phenomenon was confirmed by an indoor experiment on a simulated seafloor. An intensity-based algorithm was developed to detect shell fragments on the seafloor. The field data were analyzed by this method. Shell fragments visible on the bathymetry were detected along with smaller pieces which were not obvious on the bathymetry map. Preliminary analysis shows that the seafloor was covered by shell fragments (greater than 4 mm 2 ) with an area coverage 6.80% and 9.82% for the two sites studied. The shell size probability density distribution function is well modeled by a power-law which implies the weathering of shells is from numerous processes acting on different scales. This method provides the sediment surface information over a larger area which is difficult to acquire by conventional sediment coring.