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31 January 2002 Investigation of falling precipitation with a lidar ceilometer
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The Vaisala ceilometer LD-40 'Tropopauser' is a compact eye-safe lidar measuring continuously under all possible climatic conditions and scanning the atmosphere up to a height of 13000 m. It uses laser diodes with 855 nm wavelength that are pulsed at an average frequency of 4000 Hz. The distance of the system's range bins is 7.5 m. Its main purpose is reporting cloud base heights and vertical visibility for aviation safety purposes. Ceilometers are capable of retrieving additional atmospheric parameters. These parameters include a vertical profile of planetary boundary layer aerosol backscatter, and an estimation of the cloud coverage for all cloud layers detected. The main focus of this paper however is directed on the investigation of backscatter data from falling precipitation. The LD-40 ceilometer is able to detect virga and precipitation reaching the ground, and it can distinguish between frozen and non-frozen precipitation by examining backscatter data profiles. This ability is caused by the biaxial lidar optics in combination with the different scattering phase functions of droplets, soft hail, and snow. Results of LD-40 measurements gathered on a regular basis are presented together with comparison data obtained from precipitation and visibility meters.
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Christoph Muenkel, Jyrki Ojanpera, and Pekka Ravila "Investigation of falling precipitation with a lidar ceilometer", Proc. SPIE 4539, Remote Sensing of Clouds and the Atmosphere VI, (31 January 2002);

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