Acoustic propagation affected by environmental parameters in coastal waters

Abstract

In coastal regions various factors affect the propagation of acoustic signals such as wind, tidal effects, off shore currents and even river outflows. Shallow water waveguide is also characterised by site-specific source nature, bathymetry, sediment properties and sound speed profile. Monterey-Miami Parabolic Equation (MMPE) model has been used to study the propagation in very shallow waters of Arabian Sea with respect to environmental parameters. Sound speed Profiles (SSP) and bottom sediment samples measured at the site characterize the water column and the ocean bottom respectively. Bottom is clay (soft bottom) which can lead to absorption of acoustic intensity into the sediment leading to a decrease in reflected acoustic rays. Under these conditions propagation to large distances will be associated with

large losses in acoustic energy. Critical angle of propagation determined theoretically is found to be ±11.42^o with respect to horizontal representing low order trapped modes. SSP is downward refracting enhancing propagation along the bottom. In this paper Transmission Loss (TL) computation have been carried out for different frequencies with respect to range and depth. Signal loss and arrival structure and the travel time have been computed for different ranges from 0 to 6 km. Model results have been evaluated by comparing with field measurements and are found to be suitable for modelling extremely shallow water environments.