Directional underwater noise estimation

In the waters surrounding Australia and New Zealand, there are features of the measured three-dimensional ambient noise field (20–200 Hz) which appear similar to those found in the northern hemisphere where shipping noise is dominant. In the latter case, this shipping noise can be enhanced when vessels are at high latitudes or over sloping bathymetry. However, in the southern hemisphere, there are fewer ships, negligible numbers over suitable bathymetric slopes, and practically none at all at high latitudes. This apparent inconsistency in interpretation of the broad features between the different hemispheric noise data had led to the development of the directional underwater noise estimates (DUNES) model for ambient noise. The model includes wind-generated noise from local, bottom bounce, RSR, and RR path sources. The last sources include the high latitude winds and continental or seamount slope enhanced wind noise [R. W. Bannister, J. Acoust. Soc. Am. 79, 41–48 (1986)]. The same wind-generated surface source levels {based upon upgraded values [A. S. Burgess and D. J. Kewley, J. Acoust. Soc. Am. 73, 201–210 (1983)]} are used for each source location and when combined with an appropriate transmission process produces predictions of vertical noise directionality and resulting omnidirectional noise. Features included are a speed and frequency-dependent wind-source depth, season, latitude, depth, and bottom reflection loss dependences, and specific shipping sources, with or without slope enhancements. Comparison with vertical directionality data shows that the levels and frequency relations of the various angular components match well.