OPERATIONAL REMOTE-SENSING OF TROPOSPHERIC AEROSOL OVER LAND FROM EOSMODERATE RESOLUTION IMAGING SPECTRORADIOMETER

Daily distribution of the aerosol optical thickness and columnar mass concentration will be derived over the continents, from the EOS modera te resolution imaging spectroradiometer (MODIS) using dark land target s. Dark land covers are mainly vegetated areas and dark soils observed in the red and blue channels; therefore the method will be limited to the moist parts of the continents (excluding water and ice cover). Af ter the launch of MODIS the distribution of elevated aerosol concentra tions, for example, biomass burning in the tropics or urban industrial aerosol in the midlatitudes, will be continuously monitored. The algo rithm takes advantage of the MODIS wide spectral range and high spatia l resolution and the strong spectral dependence of the aerosol opacity for most aerosol types that result in low optical thickness in the mi d-IR (2.1 and 3.8 mu m). The main steps of the algorithm are (1) ident ification of dark pixels in the mid-IR; (2) estimation of their reflec tance at 0.47 and 0.66 mu m; and (3) derivation of the optical thickne ss and mass concentration of the accumulation mode from the detected r adiance. To differentiate between dust and aerosol dominated by accumu lation mode particles, for example, smoke or sulfates, ratios of the a erosol path radiance at 0.47 and 0.66 mu m are used. New dynamic aeros ol models for biomass burning aerosol, dust and aerosol from industria l/urban origin, are used to determine the aerosol optical properties u sed in the algorithm. The error in the retrieved aerosol optical thick nesses, tau(a), is expected to be Delta tau(a) = 0.05 +/- 0.2 tau(a). Daily values are stored on a resolution of 10 x 10 pixels (1 km nadir resolution). Weighted and gridded 8-day and monthly composites of the optical thickness, the aerosol mass concentration and spectral radiati ve forcing are generated for selected scattering angles to increase th e accuracy. The daily aerosol information over land and oceans [Tanre et al., this issue], combined with continuous aerosol remote sensing f rom the ground, will be used to study aerosol climatology, to monitor the sources and sinks of specific aerosol types, and to study the inte raction of aerosol with water vapor and clouds and their radiative for cing of climate. The aerosol information will also be used for atmosph eric corrections of remotely sensed surface reflectance. In this paper , examples of applications and validations are provided.