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We are used to using cable connections for underwater data transfer between two locations. This is the most commonly used method for long-distance transmission. However, wireless underwater data telemetry technology is currently proving capable of providing an alternative method. Acoustic modems are designed to offer a seamless interface for subsurface data transmission and are already in use in many applications.
So the technology works. But practicality is the issue in many cases where, for instance, horizontal and vertical performance is involved. A system might perform to full satisfaction in one case but a change in conditions or application may reduce performance. Optimum performance of wireless acoustic modem systems depends upon several conditions: speed of sound, water depth, existence of thermoclene zones, ambient noise and seasonal change. It appears that long-term average rates of successful transmission may fall dramatically at a range of several km in the typically adverse shallow-water acoustic channel. This might be adequate for networked acoustic modems to be cost-effective in providing quantities of data typically required for data assimilative modelling of coastal oceanographic processes. However, systems equipped with message storage and handshaking-protocol technology can improve the liability and performance of the wireless data connection.
Most systems are capable of being mounted on moving platforms such as AUVs, drifters, submarines, ships and buoys. These applications require multiphase Doppler correction algorithm in order to render them capable of compensating for relative movements between source and receiver. For longer-distance connections, network solutions with repeater stations are another possibility.
Hydro International is much indebted to all the manufacturers who contributed to this product survey, thus exposing their products to scrutiny. Some manufacturers, announced the launch of new data-communication products later this year. These are not included in this Product Survey. We would also like to acknowledge the assistance of Paul van Walree of TNO, who helped prepare the survey.
Participating Suppliers:
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