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Ali H. Omar, David M. Winker, Mark A. Vaughan, Yongxiang Hu, Charles R. Trepte, Richard A. Ferrare, Kam-Pui Lee, Chris A. Hostetler, Chieko Kittaka, Raymond R. Rogers, Ralph E. Kuehn, and Zhaoyan Liu

top-of-atmosphere radiation to relate satellite-based observations to aerosol properties by using theoretical models. These models are usually based on measurements or established climatologies (e.g., d’Almeida et al. 1991 ; WCRP 1986 ) In most cases these algorithms make assumptions about the vertical distribution of aerosols and surface reflectance, all of which have significant contributions to the top-of-atmosphere radiation. OMI ( Levelt et al. 2006 ) uses two spectral regions—17

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Yongxiang Hu, David Winker, Mark Vaughan, Bing Lin, Ali Omar, Charles Trepte, David Flittner, Ping Yang, Shaima L. Nasiri, Bryan Baum, Robert Holz, Wenbo Sun, Zhaoyan Liu, Zhien Wang, Stuart Young, Knut Stamnes, Jianping Huang, and Ralph Kuehn

prelaunch CALIPSO cloud phase algorithm, which is used in the release 2 data product, is based primarily on theoretical model simulations of lidar backscatter and polarization ( Hu et al. 2001 ). In the prelaunch CALIPSO phase algorithm, the depolarization threshold values that separate water and ice clouds are a function of layer-integrated attenuated backscatter coefficients. With this approach, we have found that horizontally oriented ice (HOI) cloud particles may be classified as either ice or water

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David M. Winker, Mark A. Vaughan, Ali Omar, Yongxiang Hu, Kathleen A. Powell, Zhaoyan Liu, William H. Hunt, and Stuart A. Young

–polarization techniques. Nevertheless, the original measurement requirements defined for CALIOP (see Table 1 ) constitute a unique and important dataset and form the core of the CALIOP data products. This overview paper provides a brief summary of the CALIPSO mission, the CALIOP instrument and data products, and the algorithms used to produce them. Few lidars have flown in space and none with the capabilities of CALIOP. Therefore, many aspects of the CALIOP algorithms are unique. We describe the conceptual basis of

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Stuart A. Young and Mark A. Vaughan

level 2 data products from the lidar are the locations of atmospheric regions containing particulate matter (clouds and aerosols), the identification of these particles according to type, and profiles and layer integrals of particulate backscatter and extinction in these regions. This paper focuses on the fully automated retrieval of profiles of particulate backscatter and extinction. Note that the level 2 algorithms covered here are applied to measurements made by a single instrument (CALIOP

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Zhaoyan Liu, Mark Vaughan, David Winker, Chieko Kittaka, Brian Getzewich, Ralph Kuehn, Ali Omar, Kathleen Powell, Charles Trepte, and Chris Hostetler

of attenuated backscatter coefficients ( Hostetler et al. 2006 ; Powell et al. 2009 ) are reported in the CALIOP level 1B data products. These level 1 profiles are further analyzed in level 2 processing to derive the optical and physical properties of clouds and aerosols ( Vaughan et al. 2004 ). The level 2 processing algorithms include three primary modules: a layer detection algorithm known as the selective, iterated boundary locator (SIBYL), the scene classification algorithms (SCA), and the

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Kathleen A. Powell, Chris A. Hostetler, Mark A. Vaughan, Kam-Pui Lee, Charles R. Trepte, Raymond R. Rogers, David M. Winker, Zhaoyan Liu, Ralph E. Kuehn, William H. Hunt, and Stuart A. Young

polarization plane of the outgoing beam. Each component is measured separately using photomultiplier tubes (PMTs). Additional information about the CALIOP transmitter and receiver design and operation can be found in Hunt et al. (2009) . Accurate calibration of all three lidar signals is essential for layer detection and the subsequent retrieval of layer optical properties. Complete details of all CALIOP calibration algorithms are presented in Hostetler et al. (2006) . Essential aspects of the CALIOP

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Mark A. Vaughan, Kathleen A. Powell, David M. Winker, Chris A. Hostetler, Ralph E. Kuehn, William H. Hunt, Brian J. Getzewich, Stuart A. Young, Zhaoyan Liu, and Matthew J. McGill

CALIOP profile measurements are the spatial locations of these many different types of geophysical entities. The function of the CALIOP layer detection algorithm is thus to untangle scenes such as that shown in Fig. 1 , to identify those portions of the profiles backscattered from clouds, aerosols, and/or the earth’s surface, and to clearly separate those backscattered portions from the ambient “clear air” scattering (i.e., from regions of purely molecular atmosphere). To refer in general to any of

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William H. Hunt, David M. Winker, Mark A. Vaughan, Kathleen A. Powell, Patricia L. Lucker, and Carl Weimer

1. Introduction This paper describes the design and performance of the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP), a three-channel elastic backscatter lidar that is the prime payload instrument on the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation ( CALIPSO ) satellite. It provides background material for a collection of CALIOP algorithm papers that are to be published in the Journal of Atmospheric and Oceanic Technology ( Winker et al. 2009 ). CALIPSO was

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