Sound speed and attenuation in the sea bottom from broadband sound propagation in the Yellow Sea.

Abstract

A joint China‐U.S. underwater acoustics experiment was conducted in August, 1996 in 75‐m water in the Yellow Sea with a very flat bottom and a strong and sharp thermocline. Broadband explosive sources were detonated both above and below the thermocline along two radial lines and a quarter of circle. Two inversion schemes are used to obtain the sound speed in the bottom. The first scheme is based on extracting normal mode depth functions from the cross‐spectral density matrix (CSDM). The CSDM is constructed from explosive signals measured using a 32‐element vertical line array at a fixed long range. In the second scheme, the modal arrival times are extracted using an adaptive time‐frequency analysis technique. The inverted bottom sound speed is used as a constraint on high‐quality TL data to extract the bottom sound attenuation. The inverted bottom attenuation exhibits apparent nonlinear frequency dependence over a frequency range from 80 to 1260 Hz. A possible effect of mode‐coupling on the inverted botto...