19 November 2012 Evaluation of water vapor Raman lidar signals from clouds
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Abstract
Raman lidar is commonly used for measurement of water vapor profiles in the lower atmosphere. However, the treatment of the Raman lidar signals from clouds is not well established. A simplified model taking multiple scattering into account is proposed. The model results in a difference of two exponential functions, one which represents the extinction of laser light inside the cloud, and another which represents the effect of multiple scattering. The model was applied to measurement results using a Raman lidar system consisting of a laser wavelength of 280 nm and detection channels for Raman scattering from water vapor and atmospheric nitrogen. When a cloud was present in the field of view of the lidar, the water vapor Raman scattering signal increased from almost zero at the cloud base to a maximum at a penetration distance of about 50 m, whereas the nitrogen Raman scattering signal decreased monotonously beyond the cloud base. This behavior could be explained by the model, and the measured signals could be adequately reproduced by setting the decay constant of one exponential function equal to the attenuation coefficient of the nitrogen Raman scattering signal, and optimizing the decay constant of the other exponential function. Comparison of measurement results and calculation results based on the model showed that the model is mainly applicable to optically thick clouds, for which the attenuation coefficient is larger than 0.02 m-1.
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Tetsuo Fukuchi, Tetsuo Fukuchi, Takashi Fujii, Takashi Fujii, } "Evaluation of water vapor Raman lidar signals from clouds", Proc. SPIE 8526, Lidar Remote Sensing for Environmental Monitoring XIII, 852610 (19 November 2012); doi: 10.1117/12.977293; https://doi.org/10.1117/12.977293
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