Sensitivity of PARASOL multi-angle photopolarimetric aerosol retrievals to cloud contamination

[摘要] An important problem in satellite remote sensing of aerosols is related tothe need to perform an adequate cloud screening. If a cloud screening isapplied that is not strict enough, the ground scene has the probability ofresidual cloud cover which causes large errors on the retrieved aerosolparameters. On the other hand, if the cloud-screening procedure is toostrict, too many clear sky cases, especially near-cloud scenes, will falselybe flagged cloudy. The detrimental effects of cloud contamination as well asthe importance of aerosol cloud interactions that can be studied in thesenear-cloud scenes call for new approaches to cloud screening. Multi-anglemulti-wavelength photopolarimetric measurements have a unique capability todistinguish between scattering by (liquid) cloud droplets and aerosolparticles. In this paper the sensitivity of aerosol retrievals frommulti-angle photopolarimetric measurements to cloud contamination isinvestigated and the ability to intrinsically filter the cloud-contaminatedscenes based on a goodness-of-fit criteria is evaluated. Hereto, an aerosolretrieval algorithm is applied to a partially clouded over-ocean syntheticdata set as well as non-cloud-screened over-ocean POLDER-3/PARASOLobservations. It is found that a goodness-of-fit filter, together witha filter on the coarse mode refractive index (m_r^coarse> 1.335) and a cirrus screening, adequately rejects the cloud-contaminatedscenes. No bias or larger SD are found in the retrieved parameters for thisintrinsic cloud filter compared to the parameters retrieved in a priori cloud-screened data set (using MODIS/AQUA cloud masks) of PARASOL observations.Moreover, less high-aerosol load scenes are misinterpreted as cloudcontaminated. The retrieved aerosol optical thickness, single scatteringalbedo and Ångström exponent show good agreement with AERONETobservations. Furthermore, the synthetic retrievals give confidence in theability of the algorithm to correctly retrieve the micro-physical aerosolparameters.

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