Improved equivalent fluid approximations for a low shear speed ocean bottom

The acoustic reflection coefficient for a homogeneous fluid over a homogeneous solid with a low shear speed can be well approximated by replacing the solid with a fluid with suitably chosen parameters. It is shown that previous expressions for the density of this equivalent fluid can be replaced with a single expression which covers a wider range of practical cases. It is further shown that the use of a complex density gives an equivalent fluid which closely reproduces the reflection coefficient of typical soft solid seabeds.