Measurements of mid-frequency bottom-interacting signals and geoacoustic inversion in Jinhae Bay, Southeast Korea

Abstract

Measurements of bottom-interacting signals over a frequency range of 4–12 kHz were made at two different sites in shallow water off the southeast coast of Korea. Although the distance between the sites was less than 20 km, the geological properties of surficial sediments were different. The surficial sediment at the site located on the north side was dominated by mud, and the measured bottom loss showed typical characteristics of sediment with a sound speed lower than the water sound speed. In addition, some interesting arrivals, which seemed to be reflected from a sub-sediment interface, were observed immediately following bottom arrivals in the frequency range of 4–8 kHz of some datasets. In contrast, sediment at the site located to the south was dominated by sandy mud, and the bottom loss showed typical characteristics of sediment with a higher sound speed. Geoacoustic parameters of surficial sediment were estimated using a simulated annealing method with an objective function comparing the measured bottom loss data with the Rayleigh reflection model. Surficial layer thickness was estimated based on arrival-time differences between bottom reflected and sub-bottom reflected signals. Inversion results are discussed in comparison with a bottom model constructed based on seismic data and core samples.