Dust aerosol retrieval results from MISR

Abstract

ABSTRACT Satellite measurements provide important tools for understanding the eect of mineral dust aerosols on pastand present climate and climate predictions. Multi-angle instruments such as Multi-angle Imaging Spectro-Radiometer (MISR) provide independent constraints on aerosol properties based on their sensitivity to theshape of aerosol scattering phase functions. The current MISR operational retrieval algorithm (version 16and higher) was modi“ed by incorporating new non-spherical dust models that account for naturally occurringdust shapes and compositions. We present selected examples of MISR version 16 retrievals over AERONETsunphotometer land and ocean sites during the passage of dust fronts. Our analysis shows that during suchevents MISR retrieves Angstrom exponents characteristic of large particles, having little spectral variation inextinction over the MISR wavelength range (442, 550, 672 and 866 nm channels), as expected. The retrievedfraction of non-spherical particles is also very high. This quantity is not retrieved by satellite instruments havingonly nadir-viewing cameras. Our comparison of current (version 16) MISR-retrieved aerosol optical thickness(AOT) with AERONET instantaneous AOT shows better coverage and stronger correlations than when makingidentical comparisons with previous AOT retrievals (version 15). The MISR algorithm successful mixtures includea non-spherical dust component with high frequency in retrievals over dark water and slightly lower frequencyover land. Selection frequencies of non-spherical dust models also decrease in dusty regions aected by pollution.Keywords: MISR retrievals, atmospheric dust, optical properties of nonspherical particles