Kalashnikova, O.V., Diner, D.J., Abdou, W., Kahn, R., Gaitley, B.J., and Gasso, S., (2004). Measuring Non-spherical Airborne Dust with Space-based MISR Multi-angle Imaging. Eos Trans. AGU, 85(47), Fall Meet. Suppl. 2004, Abstract # A13B-0111
Some of the world's largest dust plumes emanate from Northern Eurasian deserts and are expected to increasingly affect Asian ergonomics. Together with field experiments, satellite observations of dust outbreaks, placed into the context of large-scale dust transport modeling, can help understand the impact of mineral dust aerosols on past and present climate and climate predictions in North and Central Asia. Multi-angle instruments such as the Multi-angle Imaging SpectroRadiometer (MISR) provide independent constraints on aerosol properties based on sensitivity to the shape of the scattering phase function. We present an analysis of the Multi-angle Imaging SpectroRadiometer (MISR) Standard Aerosol Retrieval algorithm, updated with new non-spherical dust models (Version 16 and higher). We compare the MISR products with coincident AERONET surface sun-photometer observations taken during the passage of dust fronts. Our analysis shows that during such events MISR retrieves Angstrom exponents characteristic of large particles, having little spectral variation in extinction over the MISR wavelength range (442, 550, 672 and 866 nm channels), as expected. Also, the retrieved fraction of non-spherical particles is very high. This quantity is not retrieved by satellite instruments having only nadir-viewing cameras. We assess whether MISR aerosol optical thickness (AOT) acquired at about 10:30 AM local time, can be used to represent daily mean AOT in dust climate forcing studies, by comparing MISR-retrieved aerosol optical thickness (AOT) with AERONET daily-mean values. We also compare the effect of particle shape on MISR and MODIS dust retrievals, using co-located MISR, MODIS, and AERONET AOTs and Angstrom exponents. In most cases obtained for this study, MODIS had no retrievals due to sun-glint when MISR's narrower swath observed AERONET sties on islands surrounded by dark water. For the few coincident MISR-MODIS-AERONET dark-water, dusty condition retrievals we obtained, the MISR retrievals were in better agreement with AERONET than those from MODIS. Over bright desert sites, MODIS AOTs at visible wavelengths was systematically higher than those of AERONET and MISR. MISR-derived aerosol type mixtures for these cases included non-spherical dust components with high frequency in retrievals over dark water, and slightly lower frequency over land. The frequency with which non-spherical dust models were selected by the algorithm also decreased in dusty regions affected by pollution. Both MISR and MODIS retrievals have a high fail rate over optically thick dust plumes.
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