HR: 0800h
AN: OS11A-0491    [Abstracts]
TI: Characterising the Surf Zone Wave-Breaking Environment Using Passive Acoustics
AU: * Bass, S J
EM: sbass@plymouth.ac.uk
AF: University of Plymouth, School of Earth, Ocean and Environmental Sciences, Plymouth, Dev PL4 8AA United Kingdom
AB: Preliminary results are presented of an experiment to measure the ambient sound within the surf zone through varying tidal states and wave environments. Surf zone ambient noise from 20 Hz-20 kHz is predominantly generated by breaking waves through injection of oscillating bubbles into the water column. Breaking wave noise is related to the wave energy dissipation and it has been demonstrated that passive acoustic methods are a viable means of monitoring local wave breaking. Ambient noise was recorded using an omnidirectional broad-band hydrophone deployed just above the seabed in the inter-tidal zone for a four-hour period over high water when the hydrophone was submerged. Measurements of velocities, wave heights and suspended sediment concentrations were acquired simultaneously about 2 m away from the hydrophone at the same cross-shore distance. In the frequency range of interest, 20 Hz to 20 kHz, the predominant source of noise was from waves breaking directly above the hydrophone. Simultaneous land-based video recordings of the sea surface above the hydrophone confirm that individual breaking waves are associated with discrete noise events above the ambient background noise. These noise events from individual breakers evolve with the shape of wave crests and correlate with the pressure time series at gravity and infra-gravity frequencies. Throughout the sampling period the ambient noise reflects the type of breaker, water depth and sound propagation conditions. Mean sound intensities at all frequencies vary with the water depth changes with the tide. Literature reports of ambient noise measured within the surf zone are sparse and this work contributes valuable insights into temporally varying breaking wave characteristics in the surf zone and the associated acoustic noise and propagation conditions.
DE: 4259 Ocean acoustics
DE: 4546 Nearshore processes
DE: 4560 Surface waves and tides (1255)
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting