Abstract
Abstract. A new aerosol retrieval algorithm using multi-angular total and polarized measurements is presented. The algorithm retrieves aerosol optical depth (AOD), fine-mode fraction (FMF) for studying the impact of aerosol on climate change. 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 over East Asia are constrained using the cluster analysis technique based on the AERONET sun-photometer observation over East Asia, and the fine and coarse modes are not fixed but can vary. A mixing model of bare soil and green vegetation spectra and the Nadal and Breon model for the bidirectional polarized reflectance factor (BPDF) were used to simulate total and polarized surface reflectance of East Asia. By applying the present algorithm to POLDER measurements, three different aerosol cases of clear, polluted and dust are analyzed to test the algorithm. The comparison of retrieved aerosol optical depth (AOD) and fine-mode fraction (FMF) with those of AERONET sun-photometer observations show reliable results. Preliminary validation is encouraging. Using the new aerosol retrieval algorithm for multi-angular total and polarized measurements, the spatial and temporal variability of anthropogenic aerosol optical properties over East Asia, which were observed during a heavy polluted event, were analyzed. Exceptionally high values of aerosol optical depth contributed by fine mode of up to 0.5 (at 0.865 μm), and high values of fine-mode fraction of up to 0.9, were observed in this case study.
Highlights
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 (Anderson et al, 2003; Andreae et al, 2005; Charlson et al, 1969; IPCC, 2007)
The research presented in this paper aims to prospect the possibility of simultaneously retrieving the spectral aerosol optical depth (AOD) and fine-mode fraction (FMF) using polarized remote sensing and to characterize the optical and physical properties of tropospheric aerosols and their temporal and spatial distributions over East Asia
To evaluate the performance of the developed algorithm, three different aerosol cases are selected, and retrieval of aerosol optical depth and fine-mode fraction is performed by using TOA multi-angular, multi-spectral, total and polarized measurements
Summary
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 (Anderson et al, 2003; Andreae et al, 2005; Charlson et al, 1969; IPCC, 2007). One of the greatest challenges in studying aerosol impacts on climate is the immense diversity, aerosol size, composition, and origin, and in spatial and temporal distribution (Bates et al, 2001; Dubovik et al, 2002a, 2008) One consequence of this heterogeneity is that the impact of aerosol on climate change must be understood and quantified on a regional rather than just a global-average basis (Delene and Ogren, 2002; Mishchenko and Geogdzhayev, 2007). The research presented in this paper aims to prospect the possibility of simultaneously retrieving the spectral AOD and fine-mode fraction (FMF) using polarized remote sensing and to characterize the optical and physical properties of tropospheric aerosols and their temporal and spatial distributions over East Asia.
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