Features of ambient noise in shallow water

TitleFeatures of ambient noise in shallow water
Publication TypeJournal Article
Year of Publication1997
AuthorsCato, Douglas H.
JournalShallow Water Acoustics
EndNote Rec Number2627
Keywordsambient noise

This paper describes the main features of shallow water ambient noise in temperate and tropical waters around Australia, which may be indicative of shallow water noise elsewhere in the Asia Pacific region. The ambient noise is characterised by a wide range of temporal and spatial variability due to the variety of sources and propagation conditions. Variation in level exceeds 30dB at times, while variation of around 20dB is common. High levels of traffic noise have been observed near ports and along shipping routes, but in some areas near Australia where shipping concentrations are low and long range propagation is poor, traffic noise is negligible. Wind dependent noise is then the dominant component at low frequencies. In tropical waters, noise from biological sources is usually the dominant component of the ambient, in the absence of high winds and heavy rain. Diurnally varying biological choruses, that result when large numbers of animals are calling, occur regularly in both temperate and tropical waters. These are evident in the frequency range 50Hz to 3kHz and cause increases in noise level of up to 30dB, the most common time of occurrence being after sunset. At ultrasonic frequencies, snapping shrimp noise is usually dominant up to frequencies of at least 300 kHz where habitats are favourable, but shows large variation over short distances. Whale sounds are becoming an increasingly important component of ambient noise as their number increase.