Ultrasonic Ambient Noise in Australian Shallow Waters at Frequencies up to 200 kHZ
Abstract
Little is known of ambient noise in the ocean at frequencies above 50 kHz and there are few measurements above 20 kHz. The results of this study indicate that the sustained ambient noise at frequencies up to 200 kHz in temperature and tropical waters of depths less than about 60 m is characterized by the numerous sharp transient sounds of snapping shrimps. These transients have pulse widths of typically 3 to 8 micros (at one-third the peak voltage)and their bandwidth extends to well in excess of 200 kHz. Large variations in shrimp noise are to be expected over relatively short distances (hundreds of metres) as habitats change and hence shrimp numbers vary. Highest noise levels are to be expected near the bottom and where there ire coral or rock outcrops, shells, sponges or debris to provide shelter for shrimps. Noise measured under these conditions exceeded a peak level of 140 dB re 1 microPa2 at an average of about 20 pulses per second and exceeded 150 dB re 1 microPa2 at an average of 3 to 4 pulses a second. Lowest noise levels have been observed over uncluttered mud or sand. Shrimp noise shows little diurnal or seasonal variation.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 01, 1992
- Accession Number
- ADA251679
Entities
People
- Douglas H. Cato
- Michael J. Bell
Organizations
- Defence Science and Technology Group