Offres d'emploi

Polarimetry and spectroscopy to reveal the intrinsic depolarization of dust aerosol in laboratory

Type de contrat : CDD
Entreprise : ILM / Lyon
Fonction : Post-doctorat

Description du poste : Scientific context and motivations As underscored by the latest IPCC report (IPCC, 2013), atmospheric aerosols are complex physical objects that may somewhat counterbalance the warming effect of most greenhouse gases. However, to draw such a conclusion, the interaction of light with such complex systems should be first quantified. The dust aerosol is indeed a complex physical object, presenting a wide range of sizes, a highly irregular shape, sometimes with sharp edges and surface roughness, which prevents from analytical solutions to the Maxwell’s equations (Mishchenko et al., 2002), thus limiting our ability to quantify the interaction of such complex systems with the electromagnetic field. Light scattering numerical simulations exist but rely on assumptions that should be carefully checked. Hence, while light backscattering is of prime importance as involved in future satellite lidar missions (MESCAL, Earth Care or ACCP) as underscored by CNES in France, it is only recently that light backscattering has been observed in laboratory for particles embedded in ambient air (Miffre et al., 2016) where a unique (UV, VIS) polarimeter operating at specific lidar Pi-backscattering angle has been designed. This Pi-polarimeter quantifies the particles deviation from isotropy through accurate particle depolarization ratio (PDR)-measurements. Not only polarimetry is involved but also spectroscopy as PDR-measurements are currently performed at several wavelengths, covering the UV and VIS spectral ranges (Miffre et al., 2016). Work plan The present call is aimed at extending this unique laboratory Pi-polarimeter to the IR spectral range to quantify the PDR-spectral dependence, which is key for aerosol identification (Burton et al., 2016). More precisely, fundamental laboratory intensive work is required to address the dust aerosol PDR at exact backscattering angle for each definite property (size, origin). Starting from the existing laboratory Pi-polarimeter (Miffre et al., 2016), the candidate will then contribute to develop a Pi-polarimeter in the IR spectral range. To reveal the intrinsic PDR of mineral dust by accounting for its complexity, the candidate will minimize polarization and wavelengths cross-talks and evaluate the variation in the dust aerosol PDR as a function of the dust particle size and mineralogy. Such unique laboratory measurements of the intrinsic dust PDR will then be made available to a broad scientific community, in France and abroad through publications and conferences. Candidate profile To carry out this research project, candidates must hold a PhD in optics (polarimetry, spectroscopy, laser physics) and/or atmospheric physics (atmospheric aerosols, satellite remote sensing). Above all, precision is required to reveal the intrinsic ability of this complex aerosol to depolarize laser light. This 12 months’ position will be located at the Institute of Light and Matter (iLM) under the supervision of A. Miffre from the ATMOS research group (Prof. Rairoux group leader). This 12 months’ position funded by CNES will be located at the Institute of Light and Matter (iLM) under the supervision of A. Miffre from the ATMOS research group (Prof. Rairoux group leader). Contact information Alain Miffre Associate Professor in Physics at iLM Atmos Research group at ILM (Prof. Rairoux’s group)

Contact : Alain Miffre

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