Annual Report 2007

Measuring Optical Turbulence to Create a Clear Future GTRI researchers are using lidars to study the optical turbulence that makes ground-based astronomy difficult. TRI researchers are laying the foundation for techniques that could do for groundbased imaging what the Hubble Space Telescope did for astronomy. The matter under study is called optical turbulence, the distortion of light caused by its passage through the atmosphere. Optical turbulence causes stars to twinkle and a desert horizon to shimmer – and makes accurate, detailed ground-based observation of distant objects all but impossible. The phenomenon also inhibits long-range “free-space” laser applications – that is, laser light moving through the air rather than through a medium such as fiber optic cable. With a laser radar (lidar) developed at GTRI, “We can point that system in any direction in the sky and measure the strength of the turbulence effect,” said Gary Gimmestad, the Glen Robinson Chair in Electro-Optics and senior faculty leader in remote sensing technology. “That has never been accomplished before.” G The three-year Department of Defense project represents a crucial step toward controlling the effects of optical turbulence. But first, “it must be measured and characterized and monitored,” Gimmestad noted. The eventual development of algorithms or other techniques to compensate for optical turbulence could provide Earth-based telescopes with Hubble-like clarity and dramatically improve the quality of long-distance imaging, particularly for satellite imaging and surveillance. Mitigating optical turbulence could also set the stage for a range of free-space laser applications. One example cited by Gimmestad involves laser-beam data links or “free-space optical communication.” A commercial version already exists, but atmospheric effects limit its range. “At some point when you get enough optical turbulence, the whole thing becomes totally inoperative,” he said. “So again, characterizing the level of turbulence out there becomes an issue.” Another potential benefit of the work involves use of ground-based lasers to recharge satellite batteries by aiming the light at a recharging panel on an orbiting satellite. “The big problem is that turbulence is worse by the ground, right where your transmitter is, and it tends to spread the laser beam and make it wander all over the place,” Gimmestad explained. Compensating for that “spread” either at the transmission point, the receiving point or both, could not only have an enormous impact on satellites, but also open the door to a number of new laser-operated tasks. www.gtri.gatech.edu http://www.gtri.gatech.edu

Table of Contents Feed for the Digital Edition of Annual Report 2007

Annual Report 2007 Contents From the Director Research at GTRI Defense and Security Health and Human Systems Energy and Environment Manufacturing Technologies Information and Communication Technologies GTRI Around the World Interdisciplinary Research Centers The Laboratories of GTRI Georgia Tech Ireland GTRI by the Numbers GTRI and Georgia Tech Supporting Breakthrough Research GTRI Professional Education The People of GTRI

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