| << | Validation of Measurements and Models | >> |
Abstract
In April 2006 the backscatter lidar CALIOP onboard of the CALIPSO satellite was launched as part of NASA’s A-Train. The aim is to retrieve vertically resolved optical properties of clouds and aerosols, in particular profiles of extinction coefficient and particle depolarization ratio.The derivation of extinction coefficients suffers from uncertainties in the estimation of the lidar ratio. As a consequence, validation is required. As part of a validation effort in the framework of EARLINET, the Meteorological Institute of the Ludwig-Maximilians-Universität performed measurements with the Raman lidar MULIS at Maisach (48.20°N, 11.25°E). The Raman lidar methodology allows to determine extinction and backscatter coefficients without a priori knowledge of the lidar ratio.
Profiles of attenuated backscatter and of aerosol extinction coefficient as derived from MULIS and CALIOP data were compared for a limited number of case studies. In case of stable weather conditions the agreement with respect to the identification of aerosol layers is good. Only very thin aerosol layers could not be retrieved as the CALIOP signals were below predetermined thresholds. The agreement of the extinction profiles is limited – the reasons are not necessarily deficiencies of the measurements or their evaluation, but they could also be due to the distance of the sub-satellite track from Maisach. However, unrealistically high aerosol extinction coefficients retrieved from CALIOP (order of 2 km-1) let assume that the aerosol/cloud discrimination sometimes fails or that ground returns may be misinterpreted in case of strong orography. Finally, we found cases which suggest amendments of CALIPOS’s lidar ratio database.