Intercomparison between multi-angle imaging spectroradiometer (MISR) and sunphotometer aerosol optical thickness in dust source regions over China: implications for satellite aerosol retrievals and radiative forcing calculations

The multi-angle imaging spectroradiometer (MISR) aerosol optical thickness (AOT) product (tau(MISR)) was compared with sunphotometer AOT (tau(SP)) at Dunhuang (40.09degreesN, 94.41degreesE), located near the Takalamakan and Gobi dust source regions in China, during March-November 2000. This study is unique because AOT measurements from the ground are not routinely available at or near dust source regions. The tau(MISR) and tau(SP) are highly correlated, with linear correlation coefficients (R) ranging from 0.85 to 0.95 depending on the different comparison criteria used to assess the MISR retrievals. With one exception where tau(MISR) shows large differences (>0.3) when compared with tau(SP) during the passage of a dust front, all other collocated tau(SP)/tau(MISR) pairs are highly correlated with R > 0.9 and with root-mean-square error of 0.06 when retrieval conditions are favourable. Overall, tau(MISR) systemically over-estimate tau(SP) by 0.05, but they all fall within the predicted uncertainties (0.05 or 20% of tau(SP), whichever is larger). Due to diurnal change of AOT, the difference between daily averaged tau(SP) values and tau(MISR) reported during MISR overpass time is about 0.09. We discuss the implications of these results for satellite aerosol retrievals and radiative forcing studies.