Synthesis of distant signatures of underwater explosions for sea mammal hearing studies

Abstract

Experiments which measure temporary threshold shifts (TTS) in marine mammals produced by loud noises provide one means for determining the effects that underwater explosions might have on sea life in the neighborhood of the explosion [S. Ridgway et al., J. Acoust. Soc. Am. 101, 3136(A) (1997)]. In order to obtain meaningful results which do not presuppose an understanding of the possible hearing damage mechanisms, the waveforms of the noises used as stimuli in the TTS measurements should reproduce the complexities of the actual sound field experienced by sea mammals at the outer edges of the region within which significant acoustic effects on hearing are expected. Multipath arrivals and significant refractive effects complicate the far-field signals produced by explosive shock tests. For example, a large number of superimposed short impulses are often observed. In this talk a system for synthesizing distant signatures of underwater explosions will be described. The computer-controlled system takes calculated pressure-time waveforms as input and generates an acoustic simulation of the input signal. Preliminary tests to validate the operation of the system will also be reported.