Optical thickness of atmospheric dust over Tadzhikistan

Abstract

The aerosol dust optical thickness during a dust experiment in Tadzhikistan is derived from satellite measurements of reflected sunlight. The method estimates the surface reflectance on days with low optical thickness 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 directions is obtained eight days before a dust storm. Lookup tables are utilized to obtain the surface reflectance on the clear day, and another set of lookup are tables is used to assign an optical depth to the dust. The optical depth lookup tables utilize Mie scattering for a representative size distribution and index of refraction for the dust aerosol. The observed similarity of size distributions and indices of refraction for dust aerosols at many locations over the earth justify this method. A map of the dust optical thickness is given.