Sound Propagation in Water

Created by Sarah Burch (Sburch8)

How Sound Waves Travel Through Water

The physical effect of sound as it travels through the medium of water has some unique effects not found in transmission mediums such as air or a solid. Basically, a sound wave consists of a repeating pattern of high and low pressures of energy from the point of the sound’s source as it travels through a medium to a sound receiver. Sound waves, known as rays, behave differently depending on the medium that it travels through: air, water, or a solid. Salt water, as a medium for sound propagation, affects sound by changes in temperature, salinity, and pressure as these sound rays do not propagate in straight lines in the ocean, they are refracted (2). Sound speed refraction results in a bigger angle to the plane of the waves when the speed is increased and a smaller angle when speed is decreased thus these changes cause sound to become dependent in how it propagates from its source to a receiver (3).

Speed of Sound in a Medium

The speed of sound in a medium can be determined by the equation: v= (Kρ)-½ where: v is the speed of sound, K is the compressibility, and ρ (rho) is the density (1)

Examples

Figure 1 depicts typical graphs of sound speed affected by temperature, pressure, and salinity.

File:PictureofSound123.jpg

Sound speed affected by temperature, pressure, and salinity.

Fig. 1: Sound Velocity Profile (SVP): temperature vs. sound speed. Sound waves travel faster at higher temperatures and slower at lower temperatures, which can vary from 1450 to 1498 m/sec in distilled water and 1531 m/sec in sea water as sound tends to travels towards the path of least resistance as depicted in Figure 2.

Fig 2: Example of how sound moves towards the path of less resistance.

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Example of how sound moves towards the path of least resistance.

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Connectedness

The physical characteristics of how sound travels through water is fascinating because the medium of water has qualities not found in other mediums like air or a solid, which makes sound behave in an unique manner only found in water. Understanding the physics of sound transmission in water will allow me to develop better acoustic materials that can be used to absorb sound thus reducing sound transmission on ocean going vessels where sound generating from large engines can be reduced as it transmits into the ocean where it will not disturb nearby sea life. Industrial applications can consist of creating sound absorption materials to improve sound quieting, sound transmitters used by commercial vessels to determine the depth of the ocean for safe navigation, sound receivers used by vessels to detect sound energy transmitted by other vessels or marine life for research purposes.

History

Oceanographers and mariners have studied the dynamic effects of sound propagation in water to learn how sound can be used to map the ocean floor to aid in safe navigation of vessels, understand how the topography of the ocean floor affects the movement of currents, and studying the changes in temperature near the equator during El Nino an La Nina occurrences.

See also

Nature, Behavior, and Properties of Sound

Sound Barrier

Speed of Sound

Resonance

Doppler Effect

Transverse and Longitudinal Waves

Standing waves

Further reading

A Text-book of Sound by Edmund Catchpool, 1931

Rarefaction Wave Interaction of Pressure-gradient System by The Pennsylvania State University, 2007

The Sound of Waves by Yukio Mishima, 2013

External links

[1]

[2]

[3]

References

http://hypertextbook.com/facts/2000/NickyDu.shtml>. (1)

http://misclab.umeoce.maine.edu/boss/classes/SMS_491_2003/Week_10.htm (2)

http://misclab.umeoce.maine.edu/boss/classes/SMS_491_2003/sound/profile.gif (3)

http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe2.html