SWIMMERS can drown in busy swimming pools when lifeguards fail to notice that
they are in trouble. The Royal Society for the Prevention of Accidents says that
on average 15 people drown in British pools each year, but many more suffer
major injury after getting into difficulties. Now a French company has developed
an artificial intelligence system called Poseidon that sounds the alarm when it
sees someone in danger of drowning.
When a swimmer sinks towards the bottom of the pool, the new system sends an
alarm signal to a poolside monitoring station and a lifeguard’s pager. In trials
at a pool in Ancenis, near Nantes, it saved a life within just a few months,
says Alistair McQuade, a spokesman for its maker, Poseidon Technologies.
Poseidon keeps watch through a network of underwater and overhead video
cameras. AI software analyses the images to work out swimmers’ trajectories. To
do this reliably, it has to tell the difference between a swimmer and the shadow
of someone being cast onto the bottom or side of the pool. “The underwater
environment is a very dynamic one, with many shadows and reflections dancing
around,” says McQuade.
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The software does this by “projecting” a shape in its field of view onto an
image of the far wall of the pool. It does the same with an image from another
camera viewing the shape from a different angle. If the two projections are in
the same position, the shape is identified as a shadow and is ignored. But if
they are different, the shape is a swimmer and so the system follows its
trajectory.
To pick out potential drowning victims, anyone in the water who starts to
descend slowly is added to the software’s “pre-alert” list, says McQuade.
Swimmers who then stay immobile on the pool bottom for 5 seconds or more are
considered in danger of drowning. Poseidon double-checks that the image really
is of a swimmer, not a shadow, by seeing whether it obscures the pool’s floor
texture when viewed from overhead. If so, it alerts the lifeguard, showing the
swimmer’s location on a poolside screen.
The first full-scale Poseidon system will be officially opened next week at a
pool in High Wycombe, Buckinghamshire. One man who is impressed with the idea is
Trevor Baylis, inventor of the clockwork radio. Baylis runs a company that
installs swimming pools—and he was once an underwater escapologist with a
circus. “I say full marks to them if this works and can save lives,” he says.
But he adds that any local authority spending £30,000-plus on a Poseidon
system ought to be investing similar amounts in teaching children to swim.
