Applied Physics B Raman lidar for the study of liquid water and water vapor in the troposphere

Abstract. A Raman lidar system based on a tripled Nd:YAG laser is used for profiling of water vapor and liquid water in the troposphere. The Raman signals from water in the gas and liquid state are separated by interference filters and their relative intensities are studied for different atmospheric conditions. For clean weather or immediately after the rain the Raman signal from liquid water inside PBL is about one order of magnitude lower than the signal from water vapor. But during cloud measurements both Raman signals become comparable and the results of water vapor measurements must be corrected for the interference of liquid water Raman scattering. The obtained results are used for the estimation of liquid water content in the atmosphere. 42.68.Rp; 93.85.+q; 94.10.Gb; 92.60.Jq The conversion and transport of liquid water to vapor and back again is a subject of intense research. The lidars provide an unique opportunity for the atmospheric research because of the ability to monitor relatively large areas with high temporal resolution. In the last decade both DIAL and Raman systems have been successfully applied to atmospheric water studies ([1-4] and references therein). The Raman lidars, though possessing lower sensitivity as compared with DIAL systems, provide higher spatial resolution, no complicated tunable laser sources are demanded and the strong Raman line of water vapor with high frequency shift of 3657 cm −1 may be easily separated from elastic backscattering and Raman lines of other molecules. Raman method may be extended to include liquid water scattering. The knowledge of liquid water content is essential in physics of clouds, atmospheric photochemistry and in the study of condensation processes in polluted environments or in the presence of radioactive sources. Moreover, since the Raman contours of vapor and liquid water are partially overlapped, the bleed throw of Raman signal from liquid water may introduce significant errors in vapor measurements, especially when wideband excimer lasers are used for the sounding. PACS: Raman scattering by bulk water in the laboratory has been reported by a number of investigator