Geoacoustic inversion depends on relationships between geophysical and acoustic parameters. For unconsolidated granular sediments, the most reliable empirical relationship is between reflection loss and sediment density. However, there is a discrepancy between the empirical relationship and the well-known Rayleigh reflection formula (r1c1-r2c2)/(r1c1+r2c2) at normal incidence. To resolve the discrepancy, it is necessary to replace Rayleigh reflection formula with Biot’s theory for porous media. The permeability is another interesting parameter. On the geophysical side, it is connected to the shape and size of the pores and hence also the grain size and shape. On the acoustic side, it is connected with the attenuation. This because acoustic attenuation is mostly due viscous drag caused by relative motion between pore fluid and the solid grains. Therefore, there is a connection between acoustic attenuation and grain size. At least for single size grains that are approximately spherical, there is a possibility of connecting acoustic properties, such as wave speeds and attenuations, with geophysical properties, including grain size, porosity, and the material properties of the grains and fluid. [Work supported by ONR, Ocean Acoustics Program]
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