1. UNDERWATER WIRELESS COMMUNICATION

2. INTRODUCTION hydrophone
Underwater wireless communication  is a technique of sending and receiving message ,images, videos & information below water.
There are several ways of employing such communication but the most common is using hydrophones
A hydrophone
(Greek "hydro" = "water" and "phone" = "sound")
is a microphone designed to be used underwater for
recording or listening .
hydrophone

3. Definition:
Under water wireless communication is defined as the telecommunication in which the acoustic waves carry the signal below the water.

4. acoustic waves
Acoustic waves are a type of longitudinal waves that propagate by means of adiabatic compression and decompression. Longitudinal waves are waves that have the same direction of vibration as their direction of travel. Important quantities for describing acoustic waves are sound pressure, particle velocity, particle displacement and sound intensity.

5. Importance of acoustic waves rather than electromagnetic waves:
underwater communication uses acoustic waves instead of electromagnetic waves.
Because Under water communication is difficult due to factors like multi- path propagation, time variations of the channel, small available bandwidth and strong signal attenuation, especially over long ranges. In underwater communication there are low data rates compared to terrestrial communication

6. 2-D ARCHITECTURE: Sensor nodes are anchored to the bottom of the ocean
UNDERWATER ACOUSTIC SENSOR NETWORKS COMMUNICATION ARCHITECTURE:
2-D ARCHITECTURE:
Sensor nodes are anchored
to the bottom of the ocean
with deep ocean anchors.
By means of wireless acoustic
links, underwater sensor nodes
are interconnected to one or
more underwater sinks
(UW-sinks).

7. UW-sinks are equipped with two acoustic transceivers, horizontal and vertical transceiver. The first is used by the UW-sinks to communicate with the sensor nodes, while the second is used by the UW- sinks to relay data to a surface station
Vertical transceivers must be long range transceivers for deep water applications. The surface station is equipped with multiple acoustic transceivers, one for each UW-sink deployed.

8. 3-D ARCHITECTURE:
Sensor nodes float at different depths in order to observe a given phenomenon.
The possible solution to achieve different depths would be to attach each UW-sensor node to a surface buoy, by means of wires.
Multiple floating buoys may obstruct ships navigating on the surface.
They may also be easily detected and deactivated by enemies in military settings.
Due to the above reasons, each sensor is anchored to the ocean bottom and equipped with a floating buoy that can be inflated by a pump. The buoy pushes the sensor towards the ocean surface. The depth of the sensor can then be regulated by adjusting the length of the wire that connects the sensor to the anchor, by means of an electronically controlled engine that resides on the sensor.

9. ADVANCED MODEMS AVAILABLE:
CHARACTERISTCS
UWM1000
UWM2000
UWM3000
UWM4000
DEPTH(in m)
200
1000
2000
6000
RANGE(in m)
300
1500
3000
4000
POWER CON-
SUMPTION(W) 1 4 20 35

11. UNDERWATER ACOUSTIC SENSOR NETWORKS:
Underwater networks consist of a variable number of sensors and vehicles that are deployed to perform collaborative monitoring tasks over a given area.
Traditional approach for ocean bottom monitoring is to deploy underwater sensors that record data and then recover the instruments.
By this method real time monitoring is not possible, failures occur. This can be overcome by connecting underwater instruments by means of wireless links.

12. Applications of Under water communication

13. Solar powered AUV:
It is designed to provide better observation and monitoring of complex aquatic system

14. Deep Sea Observatory:
The figure above shows the concept of the deep sea observatory. At the core of the system is an underwater cable that hosts a multitude of sensors and instruments and provides high-speed connection to the surface.

15. LIMITATIONS:
Underwater sound propagation is highly affected by environmental and natural factors such as heterogeneities of the water column, variations of sound velocity versus depth, temperature and salinity, multiple and random sea reflections and significant scattering by fish, bubble clouds and plankton.

16. CONCLUSION: 
This topic gives the overall view of the necessity of underwater wireless communication and its applications.
Despite much development in this area of the underwater wireless communication, there is still an immense scope so more research as major part of the ocean bottom yet remains unexploded.
Advanced versions of the existing applications. Therefore, the main objective is to implementation of advanced technology to overcome the present limitations such as the environmental effects on the noise performance of acoustic systems as mentioned in this topic.

17. REFERENCES: 
1.  ters/oes/html/spring06/underwater.html 
2.  quest.com/html/oceans2000.pdf/
3. download_media.php?name=Aquanode.p ps 
4.  diz.pdf 

18. Any quires???

19. Thank you