The world’s most powerful 3D laser imager
Airborne laser scanning has produced stunning maps and insights in the last few years. Among others, it revealed the faint outlines of a vanished medieval city street grid obscured by the jungle surrounding Cambodia’s Angkor Wat, a feat that required 20 hours of helicopter flight time to map 370 square kilometres to a resolution of one metre.
But in a secure hangar at Hanscom Air Force Base in Bedford, Massachusetts, the belly of a Bombardier turboprop has been outfitted with technology that could pull off the Cambodian job in about half an hour. The fuselage holds a new LIDAR (light detection and ranging) 3D imaging system that works with unprecedented speed and high resolution, says Dale Fried, principal developer of the system at Lincoln Laboratory, a federally funded R&D centre run by the Massachusetts Institute of Technology.
LIDAR systems fire lasers and detect returning photons, using the timing of those return trips to measure distance and thus make 3D images. At the heart of the new imaging system is a microchip bearing the largest-ever array of pixels that detect just one photon apiece—more than 16,384 pixels in all. The array of pixels, when paired with optical lenses, allows imaging of wider areas. “Arrays of these single-photon detectors are able to map wide areas very quickly,” Fried says.
In today’s airborne LIDAR systems, individual detectors are much less sensitive; and they are mechanically moved along with the laser that emits the light to capture a wider field of view.
While no images from the new system taking shape in Hanscom are publicly available, an earlier generation of the technology—built four years ago with only one-quarter as many pixels— has been tested. The system was dispatched by the US military on a humanitarian mission after the January 2010 Haiti earthquake; a single pass by a business jet at 10,000 feet over Port-au-Prince was able to capture instantaneous snapshots of 600-metre squares of the city at a resolution of 30 centimetres, displaying the precise height of rubble strewn in city streets.
This system was already roughly four times faster and more detailed than the Angkor Wat system. But the detector array now in the Hanscom hangar is another 10 times better and could produce much larger maps more quickly, Fried says.
The technology uses a semiconductor called indium gallium arsenide, which operates in the infrared spectrum at a relatively long wavelength that allows for higher power and thus longer ranges for airborne laser scanning.