Characterization of the Environment During SAX04: Preliminary Results

The original document contains color images. Pub. in the Proceedings of the International Conference on "Underwater Acoustic Measurements Technologies and Results", held in Heraklion, Crete, Greece on 28 Jun-1 Jul 2005.

The Sediment Acoustic Experiment (SAXO4) was conducted on a sandy sediment 1- km offshore of Ft. Walton Beach, Florida, September-November, 2904. The objectives of SAXO4 were to provide a fundamental understanding of high frequency acoustic-bottom interactions sufficient to predict acoustic scattering from the seafloor, penetration of acoustic energy into the seafloor, and propagation of acoustic energy within the seafloor. For these acoustic topics a thorough characterization of seafloor properties is required The specific objectives of the team from the Naval Research Laboratory were 1) to provide statistical characterization of the environmental properties, especially the roughness and sediment volume properties; 2) measure and model the dispersive behavior of sediment sound speed and attenuation over the 1-400-kHz frequency band; 3) conduct in situ manipulative experiments to determine the effects of changing seafloor roughness on high-frequency acoustic scattering; 4) determine the effects of biological, geological, and hydrodynamic processes on the spatial and temporal distribution of sediment physical, geotechnical and geoacoustic properties; 5) develop predictive empirical and physical models of the relationships among those properties; and 6) derive a fundamental understanding of the effects of sediment microstructure (porometric and grain properties) on fluid flow and geoacoustic properties. During the 60-day experiment NRL divers made 126 dives manipulating seafloor roughness and discrete scatters, measuring seafloor properties and roughness in situ, deploying equipment of the seafloor, and collecting a variety of sediment samples. Preliminary results from SAX04 are presented.