• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

The applications of underwater acoustics and their advantages and disadvantages

Extracts from this document...

Introduction

Non-radio communications- Underwater Acoustics.

Engineering Systems: Communications ELA012

My Communications coursework will be on non-radio communications. My chosen topic is underwater acoustics. The applications of underwater acoustics and their advantages and disadvantages will be studied.  

        All forms of non-radio communications are based on waves. Waves are generally a disturbance in a surface, transferring energy from A to B. Waves can be mechanical vibrations travel through a medium. For example: water, sound. These waves are called mechanical waves. Progressive waves are created from a point and energy is distributed to the surroundings. For example: dropping a pebble in the middle of a pond causes energy to be distributed outwards. All waves can be classed into two categories:

  • Transverse waves: In Transverse waves the direction of the particle movement is perpendicular to the direction of the wave.

image06.pngimage07.pngimage00.pngimage01.png

  • Longitudinal waves: The particles in longitudinal waves travel in the same direction as the direction of the wave.

image00.pngimage08.png

Waves that can travel underwater without getting too distorted are used for comunicating underwater. Sound waves fill this criteria as they can travel long distances without getting distored too much. Sound waves are longitudnal and mechanical waves. They are longitudinal because when they travel they create an area of compression and then rarefractions within the air. A sound wave, like any other wave is introduced into a medium by a vibrating object. The motion of the particles in the medium in which a sound wave vibrates back and forth is measured by the frequency.

...read more.

Middle

So when a sound waves hits the sea bed or hits an obstacle in the sea it will reflect of it. But this is only for flat surfaces. The waves behave differently when the hit circular surfaces. When the waves hit a circular object the reflect into a center focal point. So two waves hiting a semi-circular object at oppostie ends will both reflect toa  focal point at the center of the circle.

image16.png

Waves can also changes their path by diffracting around an obstacle or when they go through an opening. This can be observed when sound can be heard around a corner. This property increases a waves ‘reach’.

image17.png

When a wave hits a different medium to what it is already travelling in, it can either speed up or slow down depending on the medium. Sound waves speed up when they travel from air to water. But underwater, waves slow down when then hit shallow water because they move away from the normal. They travel fastest in deepwater.

There are two important areas where underwater communication uses acoustics.These are:

  • Monitoring marine-life and communication between marine life.
  • SONAR.

Its is very important to monitor marine-life in the water for many different reason. Over fishing can cause a species of fish to become extint. Also if there is a sudden decrease in a population for certain species of fishes it can tell us that there is a high amount of fishing activity going on or there is another predator in the sea.

...read more.

Conclusion

If the source or destination are moving (and it is unusual to have anything at sea which is perfectly still), then the Doppler effect will 'stretch' or 'shrink' the transmitted signal.Acoustic waves travel slower in water than the electromagnetic waves discussed above, approximately 1500m/s for sound, 3x10^8 m/s for light, RF, and cable connections

Some of these disadvantages can be removed by using digital signal processing:

  • Digital filtering removes or reduces the unwanted noise signals
  • Digital processing can be used to 'ignore' reverberance and echoes
  • Array processing can be used to electronically 'steer' the receiver to point towards the best signal. 
  • Processing techniques have been developed to calculate and compensate for significant Doppler effect.

Underwater acoustics are an alternative to radio communications. Sound waves are used for this form of communication because they travel really well underwater. DSP has also ensured that the signal is clearer and there is less loss in signal. An obvious improvement would be to try to increase the strength of the sound waves. This way they can reach further without getting too distorted.

References:

Books:

  • Computational Ocean Acoustics- Jensen, Kuerman, Porter and Schmidt
  • Underwater acoustics- Albers
  • Underwater acoustics- R.W.B. Stephens

Websites:

  • www.members.aol.com/nicholash/waves/waves.htm
  • www.physicsclassroom.com/class/waves
  • www.oceanlink.island.net/oinfo/acoustics.html
  • www.lowrence.com/tutorials/sonar/sonar_tutorial_02.asp
  • http://omp.gso.uri.edu/dosits/people/defense/1.htm
  • http://flipper.ncl.ac.uk/intro.html

        Sankesh Waghray A361261

...read more.

This student written piece of work is one of many that can be found in our GCSE Waves section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related GCSE Waves essays

  1. Marked by a teacher

    Is Sunbathing Good?

    4 star(s)

    been manufactured that produced higher levels of UVB to mimic the solar spectrum and speed the tanning process. While UVB has well known carcinogenic properties and whose excessive exposure is known to lead to the development of skin cancers, recent scientific studies suggest that high exposures to the longer wavelengths UVA could also have an impact on skin cancer."

  2. Investigating into How the Depth of Water has an Affect on the Speed of ...

    I will then take an average to make sure that the surface area is constant. I will note this down to be the depth.

  1. What factors affect the strength of an electromagnet?

    changing the number of coils of wire, changing the current and changing the equipment. This is correct because on my results the higher the voltage the more distance the paperclip can jump from and also the higher the number of coils the further distance it can jump from.

  2. Deviation of Light by a Prism.

    Diagram Implementing Actual Results Obtained Before this page is all my actual results for each different angle of incidence that I measured. They are drawings of the prism itself and both the angles of incidence and the angles of emergence are labelled on them.

  1. Investigation Into How the Depth of Water Affects the Speed of a Wave.

    Height 8 2.7 2.5 2.6 2.3 2.1 2.4 Height 10 2.5 2.4 from 2.3 4.2 2.3 2.7 ANALYSIS When my graph is looked at its clear to see that the gradient of the line doesn't show any particular increase in gradient.

  2. The aim of my experiment is to see what factors affect electromagnetism the most ...

    that are used to strengthen the electromagnet. As the current increases although the amount of electrons also increase and so does the magnetic field, which in turn also increases the power of the electromagnet. So as the current increases so does the mass of paperclips being picked up by the electromagnet.

  1. Investigating the speed of travelling waves in water.

    The markers are 15 cm apart, as this gives me ample time to start and stop the clock watch, whilst observing the travelling wave. There is human error, when starting and stopping the stop clock and I estimate that this error is about 0.1 seconds as it is roughly the reaction time of a young person.

  2. Wave Motion and Definitions

    2.2.10 Conditions for Observing Interference with Light. * The Light must be COHERENT.. This may be achieved by using a laser, followed by the double slit to produce two sources. OR By using a single slit followed by the double slit.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work