A combined Rayleigh-Raman lidar for measurements of tropospheric water vapour and aerosol profiles

The receiver of the Differential Absorption Lidar system of the University of L'Aquila (Italy) has been upgraded for the detection of Raman scattering from nitrogen and water vapour induced by XeCl and XeF excimer laser lines . In this configuration, only the XeF source is activated, so we can measur e the tropospheric water vapour mixing ratio profiles with a height resolut ion of 300 m and 10 min in time. The lower limit sensitivity for the mixing ratio of water vapour is about 2 . 10(-4) and the precision ranges between 5% at 2 km and 50% at 9 km. The aerosol back-scattering ratio profiles can be measured with the same altitude and time resolution up to the lower str atosphere, the relative error is below 5% in the troposphere and about 30% at the highest altitudes. Comparisons with coincident PTU balloon-sondes sh ow that the performances of the system in measuring the tropospheric water vapour are well calibrated for studying the water vapour evolution and clou d formation in the troposphere.