The world’s most pow­er­ful 3D laser imager

SP's MAI - - TECHNOLOGY -

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.

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