Seeing Things Through Sounds

By Teh Jen Lee

The sound that comes from shrimps is music to Associate Professor John Potter's ears.

No, the National University of Singapore don is not trying to create an underwater symphony a la Disney's Little Mermaid.

Rather, together with six engineers from the Acoustic Research Laboratory of NUS' Tropical Maine Science Institute (TMSI) he has made a breathrough in underwater defence technology, by converting ambient underwater sound into images.

Possibly the first of its kind in the world, their $2.5 million project has received the thumbs-up and backing from Singapore's Defence Science & Technology Agency.

Known as the Remotely Operated Mobile Ambient Noise Imaging System, or Romanis, their invention is basically an acoustic video camera that can record silent underwater objects, well, silently.

This makes it better than existing active sonars, which can only detect targets by emitting a sound wave and looking at the reflection that bounces back. Sending out a signal would give away one's location to potential enemies.

Apart from detecting intruders, Romanis can also identify mines.

The idea behind Romais is novel -- if you don't want others to hear you, why not build a special "camera" just to look at them?

Like Human Eyes

It is similar to the way our eyes see with the light around us bouncing off objects.

Dr Potter, 46 said: "We've managed to solve tricky technical problems in elegant ways that allow us to get away with things that other people said would never work."

This cutting-edge technology relies on ambient sound in the sea, which could come from rainfall, passing ships, breaking waves and with conventional sonar signals and had to be filtered out.

And the researchers' test subject? The inedible snapping shrimps, which are typically 2 to 5 cm long.

Abundant in warm shallow waters around Singapore, they are also known as pistol shrimps because of the loud snaps they make with their claws to possibly stun prey like small fish.

Dr Potter's team has studied the characteristics of this ambient noise to come up with signal processing algorithms that can generate the best images.

In other words, snapping shrimp noises can now be used to "see" underwater.

With Romanis, images of objects up to 70m away have been successfully produced, almost twice by the previous record of 3m achieved by an earlier camera of Dr Potter's.

1,000 Times Faster Than Cable

The Romanis camera has 508 sensors with 54 networked Pentium processors to transmit data at 1.6 gigabits per second.

That is approximately 1,000 times faster than the downloading speed of cable modems.

Dr V Venugopalan, deputy head of resources at the4 acoustic lab, note that experts from at least eight fields including marine biology, physical oceanography, material science and digital signal processing were involved in the project.

Besides defence purposes, Romanis could also track and count silent whales to help protect endangered species through better management.

There have been two successful trial runs in February and May.

The first tested the system in a real sea environment while the second looked at Romanis' potential in producing images.

Dr Potter is excited about the future of Romanis.

"Romanis is a tool that can be used in a lot of different ways to explore the underwater."