OPTICAL-THICKNESS OF ATMOSPHERIC DUST OVER TAJIKISTAN

The aerosol dust optical thickness during a dust experiment in Tadzhik istan is derived from satellite measurements of reflected sunlight. Th e method estimates the surface reflectance on days with low optical th ickness for the same ground area where dust occurs. In order to avoid changes in the surface bidirectional reflectance between the dusty and clear days, nearly identical geometry between the solar and view dire ctions is obtained eight days before a dust storm. Lookup tables are u tilized to obtain the surface reflectance on the clear day, and anothe r set of lookup are tables is used to assign an optical depth to the d ust. The optical depth lookup tables utilize Mie scattering for a repr esentative size distribution and index of refraction for the dust aero sol. The observed similarity of size distributions and indices of refr action for dust aerosols at many locations over the earth justify this method. A map of the dust optical thickness is given.