It seems like something from James Bond: to be able to track objects moving when they are out of view hidden around a corner. And yet this is exactly what researchers have managed to do. A team from Heriot-Watt University, Edinburgh, has developed a camera that logs individual photons, which allows them to track objects moving out of sight.
“The system works by sending light from the camera towards the hidden object or person, and getting it back again,” explains Genevieve Gariepy, who coauthored the paper published in Nature Photonics, in a statement. “By measuring the time it takes to return to the camera, we know how far away the object is. By recording the shape of the laser ‘echo,’ we know what direction it’s coming from. It takes only a second for the camera to record all of this: so if the object is moving, we can follow it.”
Previous studies have shown that it is possible to identify objects hidden out of view, but these methods require time to receive and decode all the information, and so limit the camera's ability to track objects as they move. This new technique, however, receives enough information in one second to work out where the object is, enabling the team to be able to track hidden objects as they move in real time.
The camera used is some really specialized kit, probably not available on your local high street. Able to register the position of an individual photon, it records at an astonishing 20 billion frames per second. This allows the researchers to set the camera near to the corner around which they want to peer, then bounce a simple laser beam off the floor near to the corner. This produces an “echo” of photons that spread out around the point at which the laser hits the ground.
When the photons hit the hidden object, the tiny foam man in the video above, they bounce back from behind the corner and into the field of view of the camera. It is this pattern of returned photons that the camera can measure. This alone can’t identify the object though – as a solid wall will also reflect the photons – but if the object in question is moving, then the camera can record the changes in the patterns of photons detected.
This is different from previous methods that have attempted to build up 3D images of static objects hidden out of sight, which have required longer periods of time to create the overall picture. The new study instead focuses on how to track objects, but not necessarily on knowing what that object is.
The researchers hope that the technology could be used in disaster zones, where going on the ground might been too dangerous, or even in vehicles for seeing around corners. “We’ve already increased the distance from which the camera system will work, which is over several meters,” says Daniele Faccio, who led the study. “We’re also focusing on how we could attempt 3D reconstruction of the objects captured by the camera.”
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