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Multidirectional visible and shortwave infrared polarimeter for atmospheric aerosol and cloud observation: OSIRIS (Observing System Including PolaRisation in the Solar Infrared Spectrum)

The aim of this project is to improve the characterization of radiative and microphysical properties of aerosols and clouds in the atmosphere. These two atmospheric components and their interactions are among the main sources of uncertainty in the numerical forecast of climate change. In this context, we have designed a new airborne polarimeter for measuring directional, total and polarized radiances in the 440 to 2200 nm spectral range. This instrument is based on the POLDER concept, instrument that is currently aboard the PARASOL microsatellite. This new sensor consists in two optical systems for the visible to near infrared range (440 to 940 nm) and the shortwave infrared (940 to 2200 nm). Each optical system is composed of a wide field-of-view optics (114° and 105° respectively) associated to two rotating wheels for interferential filters and analysers respectively, and a 2D array of detectors. For each channel, the total and polarized radiances are computed using the measurements performed with the three analysers shifted by an angle of 60°. Thanks to the large field of view of the optics, any target is seen under several viewing angles during the aircraft motion. This type of instrument has been designed for the retrieval of optical thickness and microphysical properties of aerosols as well as for the determination of microphysical, macrophysical and radiative properties of clouds. In this paper, we will present this new instrument design and some preliminary results recently obtained during the first field campaign in May 2008 over Europe.