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Lidar system focuses on the weather

14 Sep 2005

Engineers develop LIDAR apparatus that can profile atmospheric humidity up to 10,000 m above the ground.

German firm Kayser-Threde has installed what it claims is the first LIDAR system of its kind at a meteorological observatory in Lindenberg near Berlin. By continuously profiling atmospheric humidity between 100 and 10,000 m above ground level, the unit is said to benefit weather prediction and improve the accuracy of satellite-based measurements.

Conventionally, humidity data is gathered using radiosondes, balloon-borne instrument platforms with radio transmitting capabilities, which are launched from the weather station every six hours. The big advantage of the LIDAR unit is that it allows frequent and hassle-free measurements.

Dubbed RAMSES, the LIDAR apparatus features an ultraviolet laser emitting at 355 nm and analyses Raman signals at 387 nm and 408 nm, which correspond to nitrogen and water vapour, as well as elastic backscatter signals at 355 nm. The system uses two telescopes, a far field telescope with an 80 cm aperture and a near field telescope with a 20 cm aperture, to monitor the troposphere - the atmospheric region close to the earth's surface containing rising and falling packets of air. Signals are detected using photomultiplier tubes.

"The main challenge was to develop a hands-off system that can be operated for extended periods," Volker Klein of Kayser-Threde told Optics.org. "A local network of three computers performs real-time data storage, continuous housekeeping, as well as processing and calibration of the raw data using information from local radiosondes."

Currently in its testing phase, RAMSES can track the passage of frontal weather systems, such as severe cold fronts, with a time resolution down to 10 seconds. Klein says that future developments include day and night operation, thanks to the robust nature of the unit, and the addition of further data channels to monitor atmospheric temperature.

Author
James Tyrrell is reporter on Optics.org and Opto & Laser Europe magazine.

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