Water vapor is one of the most important greenhouse gases; it causes about two third of the natural greenhouse effect of the Earth’s atmosphere. To improve the understanding of the role of the water vapour in the atmosphere, extensive water vapour profiles with high spatiotemporal resolution are necessary. Observations of the water-vapor mixing ratio in the lower atmosphere and its temporal evaluation have been made with a ground-based Raman lidar system in Athens, Greece (37.9°N, 23.6°E, at 200m asl.). The moisture structure, observed up to an altitude of 5-6 km and over a 150 min period during nighttime, showed temporal variations of several atmospheric features which could not be resolved by the locally available radiosoundings. The system is based on a frequency tripled Nd:YAG laser, witch emits simultaneously pulses of 75 mJ and 130 mJ output energy at 3 different wavelengths (355,532 and 1064 nm), respectively with a 10 Hz repetition rate. The optical receiver is a Cassegrainian reflecting telescope with a primary mirror of 300 mm diameter and of focal length f=600 mm, directly 10 coupled, through an optical fiber, to the lidar signal detection box.

The detectors are operated both in the analog and photon-counting mode and the spatial raw resolution of the detected signals is 15 m. Water vapor mixing ratio measurements are retrieved from simultaneous inelastic H₂O and N₂ Raman backscatter lidar signals at 387, 607 nm for N₂ and 407 nm for H₂O. Systematic measurements are performed since May 2006. A specially-developed software code will be used to retrieve water vapor profiles. All the lidar observations are complemented with radiosondes launches. Radiosondes data from the meteorological station in “Hellinicon” (37. 54° N, 23.44° E, at 15m asl) in Athens, Greece are used. The radiosondes are carried out daily at 00:00 UTC and 12:00 UTC. Systematic results (mostly cases studies) of the intercomparison between water vapor lidar profiles and radiosondes profiles will be presented. Poster Presentation Acknowledgements: This work was co-funded by the European Union – European Social Fund (75%) and National Resources (25%) of the Greek Ministry of Development, GSRT/PENED (03-ED-169) Project and Raymetrics SA., in the frame of Measure 8.3 - Operational Program "COMPETITIVENESS" of the Community Support Framework (2000-2006).