Abstract
ENEA is planning to develop a lidar system for measurement of the vertical profi le of water vapour mixing ratio in daytime at a remote site, the Station for Climate Observations located in Lampedusa, Italy. The Raman lidar technique has been retained because of its experimental simplicity with respect to DIAL, and the UV spectral range has been chosen because Raman cross-sections and detector effi ciencies are larger. For a wavelength larger than ~ 300 nm the signal is limited in daytime by sky background, but extinction is acceptable, and the aims of the system can be reached with a strong laser source. The 355 nm wavelength of a frequency-tripled Nd:YAG laser has been retained as this laser source permits to reach a large pulse energy while keeping the system simple to operate. Geometrical form factor calculations need to be performed to evaluate the near-range overlap between the laser beam and the fi eld-of-view of the receiver. Among several options, a dual-receiver system has been retained to account for the several orders of magnitude expected in the backscattered signal intensity: a smaller receiver, with a primary mirror of 200 mm diameter for the 0.2-1 km range, and a larger 500 mm receiver for the 1-3 km range.
Highlights
Water vapour plays an important role in several meteorological and climate processes, and it can be considered one of the most important substances present in the atmosphere
Energy and Environment (ENEA) is planning to install in Lampedusa a lidar system for measurement of the vertical profile of water vapour mixing ratio, based on the Raman technique: this technique is based on a shift in received wavelength to identify the scattering molecule
Besides Raman lidar, another possibility is available for water vapour measurements: DIfferential Absorption Lidar (DIAL) in the near infrared (Browell et al, 1979; Browell, 1983; Senff et al, 1994; Kiemle et al, 1997; Giez et al, 1999; Wulfmeyer, 1999; Wulfmeyer and Walther, 2001a,b)
Summary
Water vapour plays an important role in several meteorological and climate processes, and it can be considered one of the most important substances present in the atmosphere. A lidar is based on the emission of light pulses into the atmosphere and on the measurement of the radiation backscattered by the atmospheric layers under investigation. ENEA is planning to install in Lampedusa a lidar system for measurement of the vertical profile of water vapour mixing ratio, based on the Raman technique: this technique is based on a shift in received wavelength to identify the scattering molecule. Raman lidar measurements of water vapour have been performed by Vaughan et al (1988); Whiteman et al (1992); Goldsmith et al (1998); Bisson et al (1999), and many others. That the difficulty of reaching larger altitudes may constitute a limitation for the study of planetary boundary layer meteorology
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