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Forschungszentrum Jülich - Research in Jülich 2_2012

2|2012 Research in Jülich 9 radicals. The first is based on the fact that the intensity of laser light is reduced by the OH radicals, that means it is ab- sorbed. The second method uses a laser to excite the OH radicals, causing them to fluoresce.” In an effort to ensure that enough of the rare hydroxyl radicals are recorded by the first method, the researchers reflect a laser beam back and forth more than a hundred times between mirrors placed around twenty metres away from each other. “Such a setup is used, for example, in our atmosphere simulation chamber SAPHIR – and in other locations where we have enough space,” explains Hof- zumahaus. The second method is just as accurate but requires less space, making it an ideal candidate for the Zeppelin’s top platform, which is around five metres long. “Being able to use two different methods has the great advantage that we can verify the results obtained with the two measuring techniques against each other,” says Andreas Hofzumahaus. The second laser setup is not affected by changes in temperature or air pressure and functions perfectly at increasing alti- tudes on board the Zeppelin. The credit for this goes to engineers at Jülich’s Cen- tral Institute of Technology (ZAT). They first reduced the weight of the setup as a whole. “For aircraft transport, every gram counts – our aim was therefore to reduce the weight over and again,” says Knut Dahlhoff from ZAT. However, the equip- ment must remain robust. “The original ground instrument made a pretty reliable impression. But every time the ambient temperature dropped by only two de- grees, it had to be readjusted,” Dahlhoff recalls. Together with colleagues from the Fraunhofer Institute for Laser Technology in Aachen, they developed a unique preci- sion instrument that is light, compact and also robust enough for use on the long Zeppelin flights. The team of scientists and engineers also scored a similar success with an in- strument that determines how polluted COVER STORY | PEGASOS The flight routes were determined by existing scientific ground meas- uring stations. They supplement the data acquired with the Zeppelin NT. The airship took the east route to Italy and back. GERMANY THE NETHERLANDS Rotterdam Lyon Ozzano Friedrichshafen AUSTRIA SWITZERLAND ITALY SLOVENIA As of: 20 July 2012

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