Geoacoustic inversion using low and mid frequency bottom reflected signals in shallow water off the east coast of Korea

Abstract

Two types of short-range propagation experiments were conducted in shallow water (nominal water depth of 150 m) off the east coast of Korea, using 6 to 10 kHz CW signals and low-frequency broadband bulb implosion as acoustic sources. The received signals were recorded on the vertical line arrays at ranges shorter than 500 m. A marine geological observation conducted at the experimental site showed that there was a thin surficial sediment layer with thickness of less than 1 m overlaying the thicker and higher speed sediment layer and the basement was 15-20 m under the water-seabed interface. Bottom reflection loss as a function of grazing angle and frequency were estimated from the single bottom-interacting path of CW signals, which were used for the inversion of geoacoustic parameters for the surficial sediment structure. The geoacoustic inversion for parameters corresponding to the lower interface was performed using the bulb implosion data. The arrival time difference and the amplitude ratio between the single bottom-reflected and sub-bottom-reflected signals were used to estimate the sound speed and attenuation coefficient, respectively, within the second layer. [Supported by ADD (Agency for Defense Development, Korea), and KORDI (Korea Ocean Research and Development Institute)]