Optical characteristics of dust and smoke aerosols observed with multi-wavelength Raman lidar in Tokyo

We have been carrying out multi-wavelength Raman lidar observations at Etchujima campus (35.66degreesN, 139.80degreesE) of Tokyo University of Marine Science and Technology (TUMST) since early 2003. The lidar system is based on two pulsed Nd:YAG lasers which emit at 355, 532 and 1064-nm wavelength. In the spring of 2003, we acquired data sets for particular regional aerosol events: Asian dust and Siberian forest-fire smoke. These data show clear signatures of the optical characteristics for each aerosol type. In the highly depolarizing Asian-dust layer, the spectral dependence of backscatter and extinction coefficients is low and hence the extinction-to-backscatter ratio (lidar ratio) at 355 nm is close to that at 532 nm. On the other hand, in the case of smoke layer, we found that the spectral dependence is high for the backscatter coefficient, but low for the extinction coefficient. As a result the lidar ratio at 355 nm is considerably lower than the one at 532 nm. We also found the smoke layer had a small but non-negligible depolarization ratio. An inversion algorithm was used to derive microphysical properties of the smoke aerosol.