Estimation of received pulse from sea bottom with a transition layer using elastic finite difference time domain method

Abstract

Recently, ocean acoustic thermometry is being planned in shallow water. Characteristics of sound propagation in shallow water are influenced by bottom media because sound propagation is affected by acoustic boundary conditions of the water-sediment interface. To investigate characteristics of sound propagation in shallow water, it is necessary to develop an accurate numerical method to model sound propagation. Elastic finite difference time domain method (elastic FDTD) is very accurate and is useful for range-dependent models in shallow water. Therefore, we calculate the sound waveform reflected from the sea bottom with a transition layer in shallow water using elastic FDTD. It is assumed that a 1.5-kHz transducer is placed at 50-m depth. The influence of the sea bottom with the transition layer is calculated for a 400-m range. To determine the influence of thickness of the transition layer to sound propagation, we calculate sound pulses as transition layers of varying thickness. Results show that fluctuation of the pulse amplitude depends on the transition layer thickness if the thickness is greater than one wavelength. A sea bottom with a transition layer clearly affects sound propagation in shallow water.