Aerosol optical depth and fine-mode fraction retrieval over East Asia using multi-angular total and polarized remote sensing

摘要

A new aerosol retrieval algorithm using multi-angular total and polarizedmeasurements is presented. The algorithm retrieves aerosol optical depth(AOD), fine-mode fraction (FMF) for studying the impact of aerosol onclimate change. The retrieval algorithm is based on a lookup table (LUT)method, which assumes that one fine and one coarse lognormal aerosol modescan be combined with proper weightings to represent the ambient aerosolproperties. To reduce the ambiguity in retrieval algorithm, the keycharacteristics of aerosol model over East Asia are constrained using thecluster analysis technique based on the AERONET sun-photometer observationover East Asia, and the fine and coarse modes are not fixed but can vary. Amixing model of bare soil and green vegetation spectra and the Nadal andBreon model for the bidirectional polarized reflectance factor (BPDF) wereused to simulate total and polarized surface reflectance of East Asia. Byapplying the present algorithm to POLDER measurements, three differentaerosol cases of clear, polluted and dust are analyzed to test thealgorithm. The comparison of retrieved aerosol optical depth (AOD) andfine-mode fraction (FMF) with those of AERONET sun-photometer observationsshow reliable results. Preliminary validation is encouraging. Using the newaerosol retrieval algorithm for multi-angular total and polarizedmeasurements, the spatial and temporal variability of anthropogenic aerosoloptical properties over East Asia, which were observed during a heavypolluted event, were analyzed. Exceptionally high values of aerosol opticaldepth contributed by fine mode of up to 0.5 (at 0.865 μm), and highvalues of fine-mode fraction of up to 0.9, were observed in this case study.