Evaluation of sound propagation models used in bottom volume scattering studies

The proper evaluation of sound propagation between sources/receivers and scatterers is important in characterizing bottom volume scattering. In this article, several sound propagation models used in bottom volume scattering studies are evaluated and their results compared to the exact solution obtained through a numerical wave number integration technique. It is found that Hines' approach [J. Acoust. Soc. Am. 88, 324-334 (1990)] works well for the two isovelocity half-space case except when the grazing angle is close to the critical angle. The far-field approximation, given by Ivakin [Sov. Phys. Acoust. 32(6), 492-496 (1986)] and Mourad and Jackson [J. Acoust. Soc. Am. 94, 344-358 (1993)], has a performance depending upon the sound speed structure in the sediment. For an isovelocity slow bottom, it agrees well with the exact solution. However, discrepancies arise for an isovelocity fast bottom or a bottom with a complex sound speed structure. In addition, the appropriateness of using the equivalent surface scattering strength as a function of grazing angle in volume scattering characterizations is studied. In conclusion, precautions need to be taken in modeling both the propagation effects and the scattering mechanisms associated with the bottom volume scattering process.