Features and limitations of the Weston α parameter as a descriptor of seafloor bottom loss

Abstract

It is straightforward to prove that, for very small seafloor grazing angles, the Weston α parameter [Weston, J. Sound Vib. 18, 271–287, 1971] provides a reasonable estimate of the slope of bottom loss in dB versus grazing angle. However, for some circumstances, the descriptions of bottom loss versus grazing angle based on the Weston α parameter are valid over a considerable span of grazing angles and to large loss values. By studying the seafloor reflection in terms of impedance, and as linked to the geoacoustic parameters, greater knowledge of the features and limitations of the Weston α parameter as a descriptor of seafloor bottom loss has been obtained. This paper covers the theory, applicable to a variety of seafloor types, each of a uniform half-space. Seafloors considered include those with either fast or slow compressional speed. For fast seafloors, shear speed is considered as one of less than, near to, or greater than the water sound speed. The effects of each of compressional and shear absorption in the seafloor are considered. Numerous sample plots of bottom loss versus grazing angle are used to demonstrate the accuracy of the analysis.