Douglas H. Cato
Maritime Operations Div., Mater. Res. Lab., Defence Sci. & Technol. Organisation, P.O. Box 44, Pyrmont, NSW, 2009, Australia
This paper discusses the main features of ambient noise in shallow tropical waters near Australia and the implications for shallow water acoustics. Noise from biological sources is usually the dominant component of the ambient, in the absence of high winds and heavy rain. Noise levels fluctuate by more than 30 dB (commonly by about 20 dB) as a result of biological activity. Diurnally varying biological choruses produce the highest noise levels and are evident in the frequency range 40 Hz to 5 kHz. Snapping shrimp noise, extending to frequencies beyond 200 kHz, is the dominant component of ultrasonic noise where habitats are favorable. Biological transients (signals detectable from individual animals, usually fish and whales) are also important. Traffic noise varies from high levels near ports to negligible in areas remote from ports and where propagation is poor.