Made by-

Digisha Singhal 13bec026

Kinjal Aggrawal 13bec054

Guided by-

Dr. Mehul Naik

1. Deficiency in current communication

2. Necessity of underwater acoustic communication

3. Acoustic communication

4. Basic acoustic communication model

5. Acoustic modem

6. Applications

7. Limitations

8. Conclusion

9. References

Radio waves propagate under water at extremely lowfrequencies (30Hz-300Hz) & require large antennae andhigh transmission power.

Optical waves do not suffer much attenuation but areaffected by scattering.

Wired underwater is not feasible in all situations asshown below-:

o Breaking of wires

o Significant cost of deployment

Acoustic waves are the single best solution for communicating Under water.

Underwater Acoustics is the study of propagation of sound in water & interaction of mechanical waves that constitute with water & its boundaries.

Underwater wireless communication is the wireless communication in which acoustic signals (waves) carry digital information through an underwater channel.

Typical frequencies associated with Underwater Acoustics are 10Hz to 1MHz.

The propagation of sound in the ocean at frequencies lower than 10 Hz is not possible.

Frequencies above 1 MHz are rarely used because they are absorbed very quickly.

When no data is being transmitted, the modem stays in sleepmode, it periodically wakes up to receive possible data beingtransmitted by far end modem. This results in low powerconsumption.

Similarly when the data is to be transmitted , the modem receivesdata from its link in sleep mode and then switches to transmitmode and transmit the data.

This technology can also be used to control small, unmannedsubmarines, called Autonomous Undersea Vehicles (AUV's).

Oceanographers use acoustics to control underwater instruments and acquire the data that they collect remotely.

Underwater acoustic modems are relatively slow compared to telephone or cable modems on land.

Equipment

Autonomous Undersea Vehicles (AUVs)

Underwater sensors (UW-ASN)

A robot crawler carries amodem, a camera, and adigital signal-processing unit.

Traversing the seafloor,searches for an object.

When an object is found, sendsan acoustic signal to a ship orshore based station.

It can then be commanded totake a still frame photo,compress it and transfer theimage to an acoustic signalthat is sent back to theinvestigator.

Autonomous vehicles workingunder the ice can be controlledand their data can betransmitted to a topsidestation using underwateracoustic links.

Underwater data links can be combined with satellite data links toprovide data in real-time from instruments on the seafloor toscientists ashore.

Pressure sensors that are deployed on the seafloor can detecttsunamis.

Solar powered AUVs.

Pollution monitoring.

Battery power is limited and usually batteries cannot be rechargedeasily.

The available bandwidth is severely limited.

Underwater sensors are prone to failures because of fouling,corrosion, etc.

Highly affected by environmental and natural factors such asheterogeneities of the water column, variations of sound velocityversus depth, temperature and salinity, multiple and random seareflections and significant scattering by fish and bubble clouds.

The main objective is to overcome the present limitations andimplement advanced technology for oceanographic research andcope up with the environmental effects on the noise performanceof acoustic systems to compete with the future challenges likeeffective transmission of audio and video signals etc.

1. www.ieee.org/organizations/pubs/newsletters/oes/html/spring06/underwater.html

2. www.link-quest.com/html/oceans2000.pdf/

3. www.gleonrcn.org/pgmdownload_media.php?name=Aquanode.pps

4. www.cs.virginia.edu/sigbed/archives/akyildiz.pdf