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Most of the current aerosol retrievals from passive sensors are restricted to cloud-free scenes, which strongly reduces our ability to monitor the aerosol properties at a global scale. The presence of aerosols above clouds affect the polarized radiation reflected by the clouds, as shown by the measurements provided by the POlarization and Directionality of Earth Reflectances (POLDER) instrument. An approximate model of the polarized signal was developed and used to retrieve the Aerosol Optical Thickness (AOT) above clouds. Results obtained with this method in various regions of the world are presented. In the second part, we present additional results obtained with an improved method that allows the retrieval of a detailed microphysical model of the observed particles. The retrieved POLDER AOTs are compared to AOTs retrieved by a space-borne lidar in the case of a dust layer transported above clouds. The advantages and limitations of the different methods are discussed.