Acoustic modem



Acoustic modems are most commonly used as a basic building block in ocean technology to transmit data through water using sound. This can be achieved by sending a pulse position modulation signal to a ceramic element or sonar transducer that is acoustically coupled to the water (by covering it with epoxy inside a waterproof housing) and decoding the message on a receiving unit with a similar setup. Using this kind of simple setup you can achieve data rates of 5 to 150 bits/sec depending on environmental noise, water depth, and terrain geometry.

Distances can also be measured by these devices by measuring the time it takes to get a "ping" from one device to another. If you know the temperature, water salinity, and depth of the device then you can achieve a more accurate distance measurement by taking those factors in to account when you calculate the speed of sound as it travels from one station to another.

Example Modems

 * SAM-1: www.desertstar.com/Products_product.aspx
 * www.benthos.com/acoustic-telesonar-modem-product-comparison.asp

Devices integrating this kind of technology

Diver and Remotely operated vehicle positioning and messaging systems.

Acoustic releases that allow you to retrieve instruments from the sea floor.

Between diver low air pressure alert, signaling, and remote control devices.

Acoustic net geometry measurement system for gauging the size of a fishing net opening and accurately sampling fish populations.