2019_programme: LOW FREQUENCY NOISE SOUTH OF AUSTRALIA FROM DISTANT SOURCES IN THE SOUTHERN OCEAN

• Session: 06. Underwater Noise - Modelling and Measurements
  Organiser(s): Gavrilov Alexander, Skarsoulis Emmanuel, Taroudakis Michael
• Lecture: LOW FREQUENCY NOISE SOUTH OF AUSTRALIA FROM DISTANT SOURCES IN THE SOUTHERN OCEAN [invited]
  Paper ID: 1029
  Author(s): Zhang Z.Y., Gavrilov A.N.
  Presenter: Zhang Yong
  Presentation type: oral
  Abstract: Multi-year ambient noise data recorded south of Australia show persistently high levels at low frequencies that could not be explained by shipping or local winds. The monthly median noise levels below 80 Hz are higher in Austral summer/autumn than in winter/spring. There are two possible sources of the persistently high noise at low frequencies and its seasonal variation: the strong westerly winds in the Southern Ocean and ice-related events (e.g., glacier and iceberg calving) in and near Antarctica. Examination of the wind and ice coverage in the Southern Ocean shows that the winds south of the Antarctic polar front are one of the major sources of the low frequency noise in austral summer. The retreat of the ice-edge in summer and autumn increases the open water surface area south of latitude 60 degree South. Although the winds over this area in summer are generally weaker than that north of latitude 60 degree South, the sea surface is not shielded by sea ice and hence exposed to wind waves that generate underwater noise ducted in the near-surface sound channel. Significant correlation was observed between the noise level below 80 Hz at the edge of the southern continental shelf in Australia and wind speed south of the Antarctic polar front in summer, whereas no correlation was found in winter. Ice breakup events also remain a likely source of seasonal variation of the low frequency noise observed south of Australia. The higher air and water temperatures near Antarctica in summer cause more frequent and intense calving of icebergs from ice-shelves and icebergs. Because the underwater sound channel is near the water surface in Antarctic waters, the noise energy from the ice events is efficiently coupled into the deep sound channel and ducted northwards with small losses, leading to a higher level of ambient noise at low frequencies and its seasonal variation.
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• Corresponding author: Dr Zhang Yong
  Affiliation: Defence Science and Technology Group
  Country: Australia
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