This is going a long way past a telephoto lens:
To get 3D information such as the distance to a far-away object, scientists today bounce a laser beam off the object and measure how long it takes the light to travel back to a detector. The technique, called time-of-flight, is used in machine vision, navigation systems for autonomous vehicles, and other applications — but most have a relatively short range and struggle to image objects that do not reflect laser light well.
That’s according to a team of Scotland-based physicists — who say they’ve tackled these limitations, and have a system that can gather high-resolution, 3-D information about objects that are typically very difficult to image, from up to a kilometer away.
At Heriot-Watt University in Edinburgh, Scotland, the new system works by sweeping a low-power infrared laser beam rapidly over an object. It then records, pixel-by-pixel, the round-trip flight time of the photons in the beam as they bounce off the object and arrive back at the source.
The system can resolve depth on the millimeter scale over long distances using a detector that virtually counts individual photons.
Other approaches have better depth resolution, but the new system images objects like items of clothing that do not easily reflect laser pulses makes it useful in a wider variety of field situations, say the researchers. “Our approach gives a low-power route to the depth imaging of ordinary, small targets at very long range. This single-photon counting approach gives a unique trade-off between depth resolution, range, data-acquisition time, and laser-power levels.”
The primary use of the system is likely to be scanning static, man-made targets, such as vehicles. With some modifications to the image-processing software, it could also determine their speed and direction.
The scanner is particularly good at identifying objects hidden behind clutter, such as foliage. However, it cannot render human faces, instead drawing them as dark, featureless areas. This is because at the long wavelength used by the system, human skin does not reflect back a large enough number of photons to obtain a depth measurement.
The system is not maxed out: it could someday scan and image objects located as far as 10 kilometers away, and be miniaturized and ruggedized. “A lightweight, fully portable scanning depth imager is possible and could be a product in less than five years.”