|Vol 30 No 1||
Scattering in the ocean
L.J. Hamilton (ed), S. Anstee, P.B. Chapple, M.V. Hall and P.J. Mulhearn
Australian research in ambient sea noise
D.H. Cato and R.D. McCauley
An introduction to ship radiated noise
Seafloor data for operational predictions of transmission loss in shallow ocean areas
A.D. Jones, J.S. Sendt, P.A. Clarke and J. R. Exelby
Tales about Graeme Yates
Acoustics Australia Information
Australian Acoustical Society Information
Vol. 30, No. 1 pp 5-11 (2002)
ABSTRACT. Acoustic scattering in the ocean can arise naturally from interactions of sound with suspended particles, volume inhomogeneities, bubbles, the moving random sea surface, the seabed, and organisms, either in resonant or nonresonant processes. Measurements of backscatter stimulated via these processes by active sonar associated with these phenomena generated by active sonar devices are becoming increasingly useful as remote sensing tools in highly diverse applications. These include assessments of fish stocks and fish migration, seabed and habitat characterization, inferences of turbidity, measurements of waves and currents, and detection of objects. Some of these applications are broadly described, together with the physical scattering mechanisms involved.
Vol. 30, No. 1 pp 13-20 (2002)
ABSTRACT. Ambient noise in the ocean results from the contributions of many different sources and varies over a wide range of levels, more than 20 dB variation being common. It causes a wide variation in sonar performance and prediction methods are required for the effective design, acquisition and operation of sonars. Ambient noise in Australian waters is substantially different to that in the waters around North America and Europe where most earlier measurements of noise were made. Consequently, ambient noise prediction methods developed in the northern hemisphere are of limited use in Australian waters and there has been a continuing, though low level, research effort to categorise ambient noise in this part of the world. This paper reviews recent research on ambient noise in Australian waters in the context of earlier work. The main components of ambient noise are the noise of breaking waves at the sea surface and the noise of the marine animals. Distant shipping traffic and rain on the sea surface are also significant. Lower levels of traffic noise in this part of the world have revealed aspects of natural noise not examined elsewhere. The extraordinary range and variety of marine animal sounds are of particular interest both in the impact on sonar and the significance in animal behaviour.
Vol. 30, No. 1 pp 21-25 (2002)
ABSTRACT. Radiated noise from ships is important for naval vessels, hydrographic survey ships and oceanographic ships. This article provides a broad overview of the major sources of radiated noise, transmission paths, and noise reduction methods. Its principal objective is to introduce the reader to the topic of radiated ship noise. Many of the procedures for estimating the radiated noise form ships have been derived empirically. This paper is written to provide a general overview of the topic, rather than a detailed technical discussion.
Vol. 30, No. 1 pp 27-31 (2002)
ABSTRACT. The Maritime Operations Division (MOD) of DSTO is assisting the Royal Australian Navy in its assessment of a sonar performance prediction tool for range dependent ocean environments: TESS 2, prepared by Thales Underwater Systems (TUS). This assessment has included comparisons between acoustic transmission loss data measured by MOD at shallow ocean sites with range-dependent transmission predictions obtained by TUS based on a geophysical-based seafloor database. This task has included an assessment of the potential for an MOD in-situ technique to infer seafloor reflectivity at shallow grazing angles and provide input to TESS 2 for regions for which existing holdings of seafloor properties are sparse. Examples of comparisons are detailed in this paper. This paper also reviews the need for more detailed description of the seafloor for steep angles of incidence, and shows progress of a MOD technique for inference of seafloor properties suitable for short range transmission predictions.