2019_programme: PROPAGATION AND DIRECTIONALITY OF SOUND FROM SEISMIC AIR GUN ARRAYS IN TWO HETEROGENEOUS SHALLOW WATER ENVIRONMENTS

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  • Session: 03. Acoustic Monitoring of Ocean Environments and Processes: Biology, Ecology, Geophysics and Man-made activities
    Organiser(s): Ratilal Purnima, Miksis-Olds Jennifer
  • Lecture: PROPAGATION AND DIRECTIONALITY OF SOUND FROM SEISMIC AIR GUN ARRAYS IN TWO HETEROGENEOUS SHALLOW WATER ENVIRONMENTS [invited]
    Paper ID: 1009
    Author(s): Mccauley Robert, Cato Douglas, Noad Michael, Dunlop Rebecca
    Presenter: Cato Douglas
    Presentation type: oral
    Abstract: Over 2010 to 2014, experiments were conducted off Peregian Beach, Queensland (~ 26.5° S) and off Dongara, Western Australia (~ 29.25° S), to establish the response of southerly migrating humpback whales to marine seismic surveys. Measurements were made of the received levels of air gun signals at multiple positions at the two sites to develop empirical propagation models for use in estimating received levels at individual whales. The measurements were also used to determine the sound radiation characteristics of the arrays, including the beam patterns. Off Peregian Beach, seismic sources used were a 20 in³ (0.33 L) single air gun, a 6 gun cluster (2.1 m tow, x 1.3 m abeam) with stages of 20, 60, 140 or 440 in³ (0.33 – 7.2 L) and a 21 element commercial seismic array with ramp up stages of 40, 250, 500 and 1440 in³ to full power at 3130 in³ (51.3 L). Off Dongara, the 6 gun cluster was used. Sound propagation and sea floor properties differed significantly between and within sites. The seabed at Peregian was a mosaic of deep sand, exposed soft rock or reefs, or shallow sand (< 2 m) over the soft rock. Sound propagation across areas of shallow sand over rock and exposed rock (or reef) exceeded that over deep sand by ~ 3.5, 7.4 dB / km respectively. Seabed slope and water depth were also important. The 3130 in³ in source was highly directional, with levels increasing by 10-15 dB from forward to abeam. The Dongara site was a gradation of thin sand over limestone to deeper sand over limestone on moving offshore, with sound propagation worse (greater loss) than off Peregian. Models to predict received levels at individual whales were developed for both sites, incorporating the complexity of the propagation and the directionality of the source.
  • Corresponding author: Prof Cato Douglas
    Affiliation: Defence Science & Technology Group and University of Sydney
    Country: Australia
    e-mail:

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