Underwater ambient noise in shallow-water areas of the Indian Ocean within the tropical zone

Frequency spectra of underwater ambient noise were measured in the lagoon of a coral atoll, outside the reef, and on shallow-water banks in the tropical zone of the Indian Ocean. The measurements were performed in the frequency range from 0.003 to 9 kHz with the use of self-contained acoustic buoys and a small boat. In all of the regions studied, continuous underwater noise of biological origin was observed with spectral maxima at frequencies of 1–1.5 and 7–8 kHz. In the lagoon of an atoll, this noise was much more intense than regular dynamic noise in the ocean. The maximum noise levels were observed in the first half of night.