Retrieval of cloud properties using CALIPSO Imaging Infrared Radiometer. Part I : effective emissivity and optical depth Article - 2012

Anne Garnier, Jacques Pelon, Philippe Dubuisson, Michaël Faivre, Olivier Chomette, Nicolas Pascal, David P. Kratz

Anne Garnier, Jacques Pelon, Philippe Dubuisson, Michaël Faivre, Olivier Chomette, Nicolas Pascal, David P. Kratz, « Retrieval of cloud properties using CALIPSO Imaging Infrared Radiometer. Part I : effective emissivity and optical depth  », Journal of Applied Meteorology and Climatology, 2012, pp. 1407-1425. ISSN 1558-8424

Abstract

The paper describes the operational analysis of the Imaging Infrared Radiometer (IIR) data, which have been collected in the framework of the CALIPSO mission for the purpose of retrieving high altitude (above 7 km) cloud effective emissivity and optical depth that can be used in synergy with the vertically resolved CALIOP lidar co-located observations. After an IIR scene classification is built under the CALIOP track, the analysis is applied to features detected by CALIOP when found alone in the atmospheric column or when CALIOP identifies an opaque layer underneath. The fast-calculation radiative transfer FASRAD model fed by ancillary meteorological and surface data is used to compute the different components involved in the effective emissivity retrievals under the CALIOP track. The track analysis is extended to the IIR swath using homogeneity criteria based on radiative equivalence. The effective optical depth at 12.05 μm is shown to be a good proxy for about half of the cloud optical depth, allowing direct comparisons with other data bases in the visible spectrum. A step-by-step quantitative sensitivity and performance analysis is provided. The method is validated through comparisons of co-located IIR and CALIOP optical depths for elevated single layered semi-transparent cirrus clouds, showing an excellent agreement (within 20%) for values ranging from 1 down to 0.05. Uncertainties have been determined from the identified error sources. The optical depth distribution of semi-transparent clouds is found to have a nearly exponential shape with a mean value of about 0.5 to 0.6.

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