Playing garbled acoustic messages backwards could take wireless broadband communication beneath the waves, boosting the speed of data transfers to submarines, undersea robots and data collection devices by up to three times.

Wireless communication in the ocean is difficult because water molecules absorb radio waves very efficiently, an effect exploited by microwave ovens.

Acoustic signals travel better, but also degrade quickly due to echoes, ambient noise, swirling currents and, again, water absorbing the signals.

But a technique called acoustic time reversal can change that. The trick cleans up underwater sound signals, extending their range and capacity.

William Kuperman and colleagues at the Scripps Institution of Oceanography in La Jolla, California, US, and researchers from the NATO Undersea Research Centre in La Spezia, Italy, have been testing the technique in the Mediterranean.

Reconstructed signal
Time reversal exploits the way undersea acoustic signals typically arrive clouded by echoes that travel at different speeds. For example, a "ping" may arrive as three separate sounds

'Time reversal' allows wireless broadband under the sea