Aerosol optical depth and fine-mode fraction retrieval over China using polarized remote sensing

The impact of aerosol on climate change is considered as one of the main uncertainties in climate modeling, which has led to large efforts for improving their global monitoring. One of the greatest challenges in studying aerosol impacts on climate is the immense diversity, which make the impact of aerosol on climate change must be quantified on a regional rather than just a global-average basis. Satellite observations are only possible method to provide systematic observations. Despite this multitude of approaches, the aerosol properties retrieval from satellite data is still not satisfactory. The accuracy of remote sensing aerosol characterization is limited by the difficulty to model the local optical properties of aerosol. Multi-angle polarized measurements provide an alternative approach for the study the aerosol particles. The research presented in this paper aims to prospects the possibility of simultaneously retrieving the spectral AOD, and fine-mode fraction (FMF) over the China using multi-angular, multi-spectral, and polarized remote sensing measurements. The retrieval algorithm is based on a lookup table (LUT) method, which assumes that one fine and one coarse lognormal aerosol modes can be combined with proper weightings to represent the ambient aerosol properties. To reduce the ambiguity in retrieval algorithm, the key characteristics of aerosol model are constrained using the cluster analysis technique based on the AERONET sun-photometer observations, and the sensitivity of reflectance and polarized reflectance to aerosol microphysical optical parameters are evaluated. Based on the studies of the sensitivity, the basic theory of using the remote sensing data of multi-angular polarized to retrieve the aerosol properties is proposed. Analysis and validation of the results are presented using AERONET observations, AOD products of POLDER and MODIS.