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Advanced marine acoustics

Lecturers: Dr Alec Duncan, Prof Alexander Gavrilov
Location: Curtin University, Bentley Campus
Mode of Delivery: On-line

Prerequisites/assumed knowledge

Physics and mathematics to second year university level including an understanding of wave propagation and Fourier transforms.

Aim/learning objectives

To provide students with an understanding of the physics of underwater sound, including propagation in deep and shallow water, the interaction of sound with the seabed and sea surface, scattering from objects, rough surfaces and random inhomogeneities, and transducers for generating and receiving underwater sound.

Content

  1. Introductory material: Terminology and units of measurement; acoustic characteristics of deep and shallow water; geoacoustic models of the seabed; interaction of sound with the sea surface and seabed; ambient noise; absorption.
  2. Theoretical background: The wave equation and Helmholtz equation for fluid media; acoustic sources; Greens functions; the wave equation for elastic media; boundary conditions.
  3. Ray theory: Derivation of ray equations; methods of solution; intensity calculations; dealing with attenuation and boundary interactions; limitations of ray methods; Gaussian beam tracing; examples of ray codes.
  4. Integral transform techniques: Solution of the wave equation for layered media via the Hankel transform; solution of the depth equation; wavenumber integration methods; Pekeris waveguide; boundary waves; examples of integral transform codes.
  5. Normal modes: Mathematical derivation; methods of solution for range-independent problems; solution for Pekeris waveguide; application to range-dependent problems: adiabatic modes, coupled modes; examples of normal mode codes.
  6. Other numerical techniques: Parabolic Equation method; finite differences; finite elements; boundary elements.
  7. Rough surface scattering: Coherent and incoherent components of scattered signals; small perturbation approximation; Kirchhoff approximation; surface reverberation; computation methods and limitations.
  8. Scattering from objects in the water column: Air bubbles, solid spheres and cylinders, cylindrical and spherical shells, biological organisms; scattering within a waveguide.
  9. Scattering from random inhomogeneities: Scattering from random fluctuations in sound speed; phase and amplitude fluctuations; spatial coherence; volume reverberation; effects of scattering on signal propagation in a waveguide.
  10. Transduction: Physical and electrical properties of sonar transducers; equivalent circuit models; radiation impedance; radiation patterns.
  11. Modelling propagation of broadband and pulse-like signals: Delay and sum methods; Fourier synthesis methods.
  12. Inversion techniques: Stochastic and deterministic optimisation techniques; inversion for seabed properties; inversion for the sound speed profile; acoustic tomography; inversion for source and receiver locations.

Assessment

Submission of module exercises: 20% of total mark
Assignment 1: 20% of total mark
Assignment 2: 20% of total mark
Final test: 40% of total mark

Resources

The text for this unit is:
F B Jensen et. al. “Computational Ocean Acoustics”, Springer-Verlag, 2000.

The following books are useful references:

  • L Brekhovskikh and Y Lysanov “Fundamentals of Ocean Acoustics”, Third Edition, Springer-Verlag, 2003.
  • L E Kinsler et. al. “Fundamentals of Acoustics”, Wiley, 1982.
  • H Medwin and C S Clay, “Fundamentals of Acoustical Oceanography”, Academic Press, 1998.