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A CAMERA that lets divers see through the murkiest of waters is being
developed by a subsidiary of the aerospace company Lockheed Martin. It uses
ultrasound rather than light to produce still or moving images of its
surroundings even when divers can鈥檛 see their hand in front of their face. Its
inventors say it would be ideal for underwater mine clearance and similar
tasks.

Just as we see an object by detecting the light waves reflected from it,
acoustic cameras 鈥渟ee鈥� an object underwater by bouncing sound waves off it.
Conventional sonar, which uses ordinary sound waves to work out the direction
and distance to an object, can only achieve very low resolution. The new
acoustic camera鈥攄ubbed Sonocam鈥攗ses ultrasound, and can make out
details on the surface of any object in its sights.

This will be useful in shallow, muddy waters when a diver is looking for
something like a mine or a crashed aircraft鈥檚 recorders. 鈥淲ith light, there鈥檚 no
useful range, because the waters tend to be very murky,鈥� says Tim White, an
engineer at the Sanders company of Nashua, New Hampshire, a division of Lockheed
Martin. 鈥淲ith sonars, you don鈥檛 get the resolution.鈥�

White and his colleagues plan to make their acoustic camera small enough for
a diver to hold in his or her hands. They have tested components operating at
two ultrasonic frequencies: 1 megahertz gives a coarse picture up to a range of
about 50 metres, while 3 megahertz gives a fine picture鈥攚ith a resolution
of about 1 centimetre鈥攁t distances up to 10 metres.

Michael Buckingham, a physicist at the Scripps Institution of Oceanography in
La Jolla, California, believes a hand-held acoustic camera would be useful.
鈥淭here are a number of applications out there,鈥� he says. 鈥淭he optical visibility
can be almost zero, but an acoustic system cuts right through that.鈥�