A camera system that can look around corners and sense the position of a hidden object-with centimetre precision-and then track its movement, is described in a paper published online in Nature Photonics this week. The study may pave the way for tracking hidden objects in real time in a number of real-life scenarios, including surveillance and vehicle collision avoidance systems that can see around blind corners.
The ability to detect the 3D shape of static, hidden objects has been demonstrated in recent studies. However, the long acquisition times required by existing methods means that locating the position of moving objects and monitoring their movement in real time remains a major challenge.
The system designed by Genevieve Gariepy, Daniele Faccio and colleagues comprises two pieces of equipment: a laser and a single-photon avalanche diode (SPAD) camera, which is highly sensitive and has an ultrafast response. The authors fired a stream of short pulses of light from the laser onto the floor just in front of the corner, which were then scattered by the floor and went on to hit a hidden object (a human form made of foam 30 cm high). The light pulses reflected back off the object, into the field of view of the camera (which also points at the region of the floor in front of the corner), and are then detected and analysed. The system uses the time of flight of the light pulses and shape of the pattern of light received by the camera to provide information about the object’s position.
With this technology, the authors are able to locate the position of an object hidden behind a wall with only three seconds acquisition time, and can reliably track, in real time, the movement of an object located a metre away from the camera. They note future work could attempt 3D reconstruction of the object.