Passive acoustic characterization of the ocean bottom using a horizontal array of hydrophones

Cross-correlation functions (CCF) of ambient and shipping noise recorded by two hydrophones are known to contain valuable information about the propagation environment. This paper investigates the feasibility of quantitatively characterizing the seafloor using interferometry of the ambient noise data obtained with SHARK array during the Shallow Water 2006 (SW06) experiment. SHARK array contained 32 near-bottom hydrophones, which formed a horizontal line array with nominal hydrophone separation of 15 m. Noise CCFs have been calculated between elements of the horizontal array as well as between each element of the array and a single-hydrophone near-bottom receiver approximately 3.6 km away. Sound propagation between elements of the array has been interpreted in terms of direct and reflected ray arrivals and possibly refracted (head wave) arrivals originating at interfaces within the bottom. CCFs on the longer propagation paths between the array and the single-hydrophone receiver are controlled by waveguide effects and have been interpreted in terms of adiabatic normal modes. The warping transform of spectrograms of the measured CCFs has been used to separate the modes. Analysis and interpretation of the normal mode dispersion curves retrieved using the warping transform will be discussed. [Work supported by NSF and BSF.]