SNAPPING SHRIMP DOMINATED NATURAL SOUNDSCAPE IN SINGAPORE WATERS

Snapping shrimp dominate the high frequency soundscape in the warm shallow waters around Singapore. The noises produced by these small creatures are a result of the collapse of cavitation bubbles they produce. During the rapid collapse, the temperatures in the bubble can momentarily reach the surface temperature of the sun, and produce impulsive noise with source levels higher than 190 dB re 1 μPa @ 1m. With millions of snapping shrimp, the resulting cacophony is heard in the form of a background crackle familiar to many tropical divers. The resulting ambient noise has a heavy tailed pressure amplitude probability distribution. This has an adverse impact on the performance of acoustic sensing and communication systems that are developed using the commonly adopted Gaussian noise model. On the other hand, systems designed with a proper understanding of the snapping shrimp noise statistics are able to perform well in Singapore waters. Interestingly, snapping shrimp can also serve as sources of opportunity for acoustic sensing. For example, ROMANIS, an ambient noise-imaging camera developed at the Acoustic Research Laboratory, is able to image underwater objects using snapping shrimp noise as acoustic 'illumination'. To develop techniques for acoustic sensing in snapping shrimp dominated soundscapes, a good understanding of the spatio-temporal statistics of the noise made by these creatures is vital. We present statistical analysis of acoustic data from several experiments in Singapore waters. We discuss the spatial anisotropy that is observed and its implications on acoustic sensing. We also present point process models that accurately capture the observed temporal clustering of shrimp snaps. Contributions to Marine Science 2012: 127-134

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