Evaluation and Intercomparison of Aerosol Parameters from the SDA versus the AERONET Inversion Algorithm

Estimates of the fine mode (sub-micron) aerosol optical depth (AOD), the coarse mode (super-micron) AOD, the fine mode fraction and the fine mode effective radius can be obtained using (a) the SDA (Spectral Deconvolution Algorithm which is an operational AERONET product) and the FMC (Fine Mode Curvature) algorithm and (b) the AERONET inversion algorithm ( operational AERONET product of long standing). This separation into fine and coarse mode components is in keeping with the fact that much of aerosol optics is essentially bi-modal: it provides robust information that is one spectral order beyond the traditional analysis in terms of total AOD and classical Angstrom exponent. The SDA employs relatively high frequency measurements ( minutes between samples) of extinction spectra while the AERONET inversion employs lower frequency measurements ( 1 hour between samples) of extinction spectra and almucantar radiance. The SDA and FMC are optical retrievals while the AERONET inversion is a microphysical retrieval which backs out the fine and coarse mode components by returning to the optical domain after separating the retrieved particle size distribution into fine and coarse mode components (based on a dynamic cut-off radius). The success of the SDA has been demonstrated in the literature while there is little validation of effective radius retrieval. We compared the AERONET inversion and the SDA retrievals of the fine mode products to better understand the reasons for the systematic differences between the two approaches. This analysis was performed using long term data sets ( 10 years duration) from AERONET stations representing distinct global regions such as the Arctic, forested zones, desert environments, industrial regions and oceanic environments. The logic behind the use of these varied regions was to examine the differences between the algorithms as a function of the influence of different aerosol sources such as dust, pollution, pristine environments, mixed aerosol conditions, maritime and biomass burning environments. The inter-comparisons were carried out for different total AOD ranges and indicators of relative fine and coarse mode strength as well as cut off radius. The details of these comparisons as well as opto-physical interpretations of the differences will be presented.