Mine-sweeping method makes seabed transparent

A new technique for undersea sonar mine detection will make the seabed ‘transparent’ and eradicate the danger of buried mines, US researchers claim.

The method, invented by Dr. David Pierson from North Carolina State University with funding from the US Office of Naval Research, uses a time-reversal technique whereby an echo of a sonar ‘ping’ is broadcast in reverse. The resulting data provides a far clearer picture of buried objects than currently available technology.

The technique could replace today’s complex and often unreliable systems for modelling the seabed and environment, which require vast numbers of sonar transmitters and receivers plus costly hardware and software. The new system works independently of the composition of the seabed and needs only one simple transceiver.

The initial ping is transmitted to the ocean floor and the return echo contains information about the seabed and any other object the signal comes into contact with. The scientists record the echo, reverse it, then transmit it back to the ocean floor in a process known as time-reversal.

Sending out this echo allows measuring equipment to focus in on a fault or mine because it changes the nature of the ultrasound wave from a divergent, reflected wave issued from a defect (or mine) into a convergent wave focusing on this defect (or mine).

Pierson, the first researcher to apply the technique to undersea mine detection, improved on previous time-reversal experiments by selecting only part of the data yielded by the echo to transmit in reverse order. When this echo is recorded, data from the seabed is supressed, while data from buried objects is enhanced.

On the web