Operational Remote Sensing

JOURNAL

OF GEOPHYSICAL

RESEARCH,

VOL. 102, NO. D14, PAGES

17,051-17,067,

JULY 27, 1997

Operational remote sensing of tropospheric aerosol over land from EOS moderate resolution imaging spectroradiometer
Y. J. Kaufman,1 D. Tanri,2 L. A. Remer,3 E. F. Vermote,4 A. Chq3 and B. N. Holbenl
Abstract. Daily distribution of the aerosol optical thickness and columnar mass concentrationwill be derived over the continents, from the EOS moderate resolution imaging spectroradiometer (MODIS) using dark land targets. 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). After the launch of MODIS the distribution of elevated aerosolconcentrations, for example, biomass burning in the tropics or urban industrial aerosol in the midlatitudes, will be continuously monitored. The algorithm takes advantage of the MODIS wide spectral range and high spatial resolution and the strong spectral dependence of the aerosol opacity for most aerosol types that result in low optical thickness in the mid-IR (2.1 and 3.8 pm). The main steps ofthe algorithm are (1) identification of dark pixels in the mid-IR; (2) estimation of their reflectance at 0.47 and 0.66 pm; and (3) derivation of the optical thickness and mass concentration of the accumulation mode from the detected radiance. To differentiate between dust and aerosol dominated by accumulation mode particles, for example, smoke or sulfates, ratios of the aerosol path radiance at0.47 and 0.66 pm are used. New dynamic aerosol models for biomass burning aerosol, dust and aerosol from industrial/urban origin, are used to determine the aerosol optical properties used in the algorithm. The error in the retrieved aerosol optical thicknesses, r,, is expected to be AT, = 0.05 5 0.27,. Daily values are stored on a resolution of 10 X 10 pixels (1 km nadir resolution). Weighted andgridded 8-day and monthly composites of the optical thickness, the aerosol mass concentration and spectral radiative forcing are generated for selected scattering angles to increase the accuracy. The daily aerosol information over land and oceans [Tunr& et al., this issue], combined with continuous aerosol remote sensing from the ground, will be used to study aerosol climatology, to monitor thesources and sinks of specific aerosol types, and to study the interaction of aerosol with water vapor and clouds and their radiative forcing of climate. The aerosol information will also be used for atmospheric corrections of remotely sensed surface reflectance. In this paper, examples of applications and validations are provided. Introduction
Daily remote sensing of aerosol from satellites over theland and ocean is essential to obtain the global aerosol budget to estimate the contribution of anthropogenic emission to the aerosol budget and to the aerosol radiative forcing of climate [Charlson et al., 1992; Penner et al., 1992; Kaufman, 1995; Andreae, 19951. Because of the short lifetime of aerosol particles [Charlson et al., 19921 and the corresponding strong spatial variations in theaerosol concentration, ground-based stations cannot assess trends in the global aerosol budget. They are, though, essential in measuring the physical and optical properties of the vertical column of the ambient aerosol [Nakajima
‘NASA Goddard Space Flight Center, Greenbelt, Maryland. ‘Laboratoire d’optique AtmosphCrique, UniversitC de Sciences et Techniques de Lille, Villeneuve d’Ascq, France.‘Science, Systems and Applications Inc., NASA Goddard Space Flight Center, Greenbelt, Maryland. 4Department of Geography, University of Maryland, and NASA Goddard Space Flight Center, Greenbelt, Maryland. This paper is not subject to U.S. copyright. American Geophysical Union. Paper number 96JD03988. Published in 1997 by the

et al., 1983; Shiobara et al., 1991; Kaufman et al., 1994; Holben et al.,...