Deep-Water Ambient Noise Profiling; Marine Sediment Acoustics; and Doppler Geo-Acoustic Spectroscopy.

摘要

Deep-water ambient noise profiling Profile the spectral, temporal and spatial properties of broadband (3 Hz 30 kHz) ambient noise from the sea surface to the bottom of the deepest ocean. Develop theoretical models of the second-order spatial statistics of the noise. Marine sediment acoustics Develop a unified, physics-based model of sound wave and shear wave propagation in saturated, unconsolidated marine sediments. New focus is on very finegrained sediments (silt and clay). Doppler geo-spectroscopy Develop the use of a light aircraft as a sound source for performing inversions for the geo-acoustic parameters of the seabed in shallow water. New focus is on helicopter noise. (1) The scientific objective of the deep-water ambient noise research is to measure the second-order spatial statistics of the ambient noise in the deepest oceans as a function of depth, from the sea surface to the seabed. Regions of interest include the Mariana Trench, notably the Challenger Deep (11 km), the Tonga Trench (9 km), and the Puerto Rico Trench (8 km). Environmental and system data will also be depth-profiled, including temperature, salinity, pressure and (directly measured) sound speed, along with all system motions (translational and rotational). Theoretical modeling of the spectral, spatial and temporal properties of the ambient noise will also be performed. (2) The sediment acoustics research is aimed at developing a unified theory of wave propagation in marine sediments in the form of the dispersion relations for the compressional and shear waves. Besides the frequency dependencies of the wave speeds and attenuations, these expressions will also return the dependence of the wave parameters on the mechanical properties of the sediment, namely porosity, density, grain size and overburden pressure. A new focus is on the inter-granular forces in silts and clays and their role in controlling wave speeds and attenuations.