Interaction of Mid-to-High Frequency Acoustic Waves with a Sandy Riverbed – Estimation of Geoacoustic Parameters and Modelling of Transmission Loss

Abstract

Sediment samples collected from 3 shallow water test sites in Idukki reservoir in Kerala are used to estimate the geophysical properties such as porosity, wet bulk density, mean grain size and sediment grain size distribution. The measured geophysical properties are utilised to estimate the geoacoustic parameters, including the compressional speed and compressional attenuation based on effective fluid density model (Biot-Stoll theory), grain and viscous grain shearing model (Buckingham’s theory). The derived geoacoustic parameters are then used for modelling the transmission loss in the sediment layer. TL variation is analysed as a function of source depth in the mid-to-high frequency (5-15 kHz) band. Modelling results supports that the penetration is minimal for low grazing angles and higher penetration occurs only at grazing angles greater than the critical angle.