Introduction to Ocean Acoustics

Introduction to Ocean Acoustics

After completing the module, the learner should be able to do the following:

Physics of sound propagation

  • Explain why sound is a pressure wave
  • List and describe the important characteristics of sound waves
  • Describe the relationship between sound pressure and sound intensity

Sound Speed

  • List the factors that affect underwater sound speed (temperature, salinity, pressure)
  • Describe how sound speed changes with changes in temperature, salinity, and pressure
  • Describe typical sound speed profiles in the world's oceans and major marginal seas

Refraction and Reflection

  • Given a sound speed profile, describe how sound will refract
  • Describe the relationship between refraction and frequency
  • Describe the factors that affect sound reflection off of the seafloor or sea surface

Propagation Paths

  • Describe the surface duct, mixed layer, and sonic layer depth and their interrelationship
  • Describe sound propagation in the surface duct
  • Describe the conditions that lead to sound channels
  • Describe the deep and secondary sound channels
  • Describe the convergence zone
  • Describe factors that lead to bottom bounce

Ocean Structures

  • Describe how sound propagation is affected by oceanic fronts and eddies

Sources of Change in Ocean Acoustic Features

  • Describe seasonal and diurnal effects on ocean sound speed profiles
  • Describe the effect of large storms on ocean sound speed profiles
  • Describe the effect of internal waves and tides on sound propagation

Scattering and Absorption

  • Describe the factors that affect scattering and absorption of sound at the seafloor
  • Describe how bathymetry affects scattering and sound propagation
  • Describe how seawater absorbs sound energy
  • Describe how air bubbles affect sound propagation

Factors Affecting Detection of Sound

  • List the factors that affect the detection of sounds under water
  • List sources of ambient noise in the ocean
  • Describe the difference between spherical and cylindrical spreading of sound waves
  • Describe how sound propagation paths affect the detection of sound sources

Sensors

  • Explain the difference between active and passive sonar systems
  • Describe the strengths and weaknesses of active and passive sonar systems
  • Describe the factors that determine target strength

SONAR Equation (Advanced Topic)

  • List the variables in the sonar equation
  • Recall the difference in the sonar equation for active and passive systems
  • Describe the Figure of Merit (FOM)