The water vapour lidar in Potenza has recently joined the NDACC lidar working group. The University of Basilicata Raman lidar system (BASIL) is operational in Potenza, Italy (40°38'45"N, 15°48'32"E, 730 m above mean sea level). BASIL has been developed by the Department of Environmental Engineering and Physics (DIFA). The major feature of BASIL is represented by its capability to perform high-resolution and accurate measurements of atmospheric temperature and water vapour mixing ratio, both in daytime and nighttime, based on the application of the rotational Raman lidar technique (Behrendt and Reichardt 2000; Di Girolamo et al. 2004; Behrendt 2005; Di Girolamo et al. 2006) and the vibrational Raman technique (Whiteman 2003a,b) in the UV, respectively. Besides temperature and water vapour, BASIL is capable of providing measurements of particle backscatter at 355 and 532 nm, particle extinction at 355 nm, particle depolarization at 355 nm in both daytime and nighttime. Relative humidity measurements are obtained from the simultaneous measurements of water vapour and temperature. This ensemble of measurements makes this system very suited for the study of meteorological processes and the characterization of aerosol and cloud microphysical properties. BASIL makes use of a neodymium-doped yttrium aluminium garnet (Nd:YAG) laser source equipped with second and third harmonic generation crystals and capable of emitting pulses at 355 and 532 nm, with single pulse energies of 250 and 300 mJ, respectively; a pulse repetition rate of 20 Hz; and a pulse duration of 5-6 ns. The beam divergence is 0.5 mrad (FWHM) and the beam diameter is 8 mm. Laser beams at 355 and 532 nm are simultaneously transmitted in the atmosphere along the zenith.

The receiver is built around a telescope in Newtonian configuration (40-cm diameter primary mirror). Using dichroic or partially reflecting mirrors, the received signal is slit into eight portions: two for temperature measurements, two for water vapour and nitrogen Raman channels, two for the elestic channels (355 and 532 nm) and two portions for the determination of particle depolarization. Signal detection is accomplished by means of photomultipliers located in cascade with each interference filter, whereas detected signals are sampled by means of photon-counting units. The vertical and temporal resolutions of the rough data are 30 m and 1 minute, respectively. More details on the system setup can be found in Di Girolamo et al. (2009a) and a discussion of the capability of Raman lidars to measure humidity in presence of cirrus clouds, both below and inside the cloud, can be found in Di Girolamo et al. (2009b).


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