Retrieval of optical depth of dust aerosol over land using two MODIS infrared bands

By incorporating Mie theory derived physical characteristics of dust particles with radiative transfer model, a look up table (LUT) method was used to retrieve optical depth (at 0.55 μm) of dust storms. Self-defined spectral dependence (single scattering albedo, asymmetry factor and extinction efficiency) of dust aerosol was imbedded into atmospheric radiative model (SBDART, Santa Barbara DISORT Atmospheric Radiative Transfer) to model the effects of dust aerosol on TOA spectral radiance at band 31 and 32 of MODIS. Simulations showed that under dusty conditions (optical depth >0), brightness temperature difference (BTD, band 31-band 32) becomes negative, and monotonically decrease with the growth of optical depth, as can be used to identify and delineate dust storms in MODIS level 1B data. A MODIS scene of November 6, 2005 containing dust event was used to validate above method. By matching simulated optical depth and brightness temperature difference with satellite remotely-sensed brightness temperature difference, optical depth of dust was retrieved. The larger values appeared at the main dust regions, and small optical depth occurred at the edges of the dust. Finally, sensitivity analysis was conducted, application of this retrieval method were discussed.