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.