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C. A. Faizoun, A. Podaire, and G. Dedieu

exponent, which is an estimate of the aerosolparticle size, is derived from the spectral dependence of the optical thickness. Although the sites were locatedfar from Sahara Desert aerosol sources, the observed aerosol optical thicknesses were high, with a mean annualvalue of 0.5 at 550 rim. The spectral dependence of aerosol optical thickness is generally low, with a meanannual value of ~ngstrrm's exponent of 0.4. The aerosol optical thickness and the atmospheric water vaporcontent are both

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Akiko Higurashi and Teruyuki Nakajima

characteristics, such as the total content, composition, etc., on a global scale. A use of satellites is very effective to study aerosol optical properties on a large scale. So far, most of the aerosol remote sensing studies have been made using National Oceanic and Atmospheric Administration (NOAA)/Advanced Very High Resolution Radiometer (AVHRR) channel 1 and/or 2. Stowe et al. (1992) produced global maps of the aerosol optical thickness at wavelength of 0.5 μ m over ocean area using channel-1 radiances

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Maria João Costa, Ana Maria Silva, and Vincenzo Levizzani

Introduction The growing consciousness of the strong influence of atmospheric aerosol on atmospheric processes (e.g., Houghton et al. 2001 ), and consequently on climate, prompts local and global studies aimed at quantifying the aerosol load in the atmosphere (aerosol optical thickness: AOT), as well as aerosol optical properties. Aerosol particles play a twofold role in the atmosphere: on one hand they directly scatter and absorb solar radiation, and on the other they enter cloud

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Igor V. Geogdzhayev, Michael I. Mishchenko, William B. Rossow, Brian Cairns, and Andrew A. Lacis

the recent paper by Mishchenko et al. (1999a) . Because strong temporal and spatial variability of tropospheric aerosols may limit the accuracy of AVHRR aerosol retrievals using only channel 1 radiances ( Ignatov et al. 1995 ; Stowe et al. 1997 ), it has been suggested that the use of channel 2 as well as channel 1 radiances may improve the accuracy of retrieving the aerosol optical thickness as well as provide an estimate of the aerosol particle size ( Durkee et al. 1991 ; Nakajima and

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T. H. Cheng, X. F. Gu, L. F. Chen, T. Yu, and G. L. Tian

deviations due to the change of aerosol properties and thin cirrus optical thickness do exist. 3. Sensitivity studies To identify the thin cirrus and aerosol information content in TOA total reflectance and polarized reflectance at 0.865 and 1.38 μ m, sensitivity studies are presented. The TOA total and polarized reflectance have been calculated using the vector radiative transfer model to compare the sensitivity of TOA total reflectance and polarized reflectance to different aerosol, thin cirrus

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Christopher J. Merchant and Mark A. Saunders

dimensionless factor that scales the infrared optical thickness of aerosol for the three channels. An aerosol scale factor of 1.0 indicates channel-integrated optical thicknesses as given in Table 1 and represents aerosol typically present up to a year after a major volcanic eruptions, such as that of Mount Pinatubo in 1991 ( Lambert et al. 1993 ). The ratios of aerosol extinction to scattering cross section assumed are those chosen by Zavody et al. (1995) to represent aged volcanic aerosols. We use

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J. D. Spinhirne, J. A. Reagan, and B. M. Herman

-sectionprofiles could be evaluated. Measurements were made with an elastic backscatter ruby iidar system withcalibration by a standard target procedure. The results from 20 measurement cases are presented. Forlayer-aerosol optical thicknesses ~ 0.04, useful results were obtained, and corroboration by solarrudiometer aerosol optical depth data was found. The mean mixed-layer aerosol extinction-to-backscatterratio for the measurements was 19.5 sr with a standard deviation of $.3 sr. With the use of an aerosol

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Ming-Dah Chou, Pui-King Chan, and Menghua Wang

surface. Over oceans, the surface reflectivity is small and aerosol optical properties can be estimated much more reliably than that over land. The Total Ozone Mapping Spectrometer (TOMS) retrieves the aerosol distribution over both land and oceans by means of aerosol index, which is related to the aerosol optical thickness and the single scattering albedo ( Herman et al. 1997 ). Distributions of aerosols over global oceans have been derived from various satellite radiance measurements. For example

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Michael D. King, Harshvardhan, and Albert Arking

observations, on the reflection, transmission and absorption of radiationby the stratosphere as a function of latitude, optical thickness and aerosol size distribution. Results arepresented and parameterized for each of two wavelength intervals in the shortwave region and 17 wavelengthintervals in the longwave region for three models of the aerosol size distribution. They include one modelrepresenting the unperturbed stratospheric aerosol plus two models based on measurements of the El Chichonaerosol size

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Akiko Higurashi, Teruyuki Nakajima, Brent N. Holben, Alexander Smirnov, Robert Frouin, and Bernadette Chatenet

evaluation of the aerosol climate forcing, since satellite retrievals can generate spatially and temporally homogeneous global distributions of aerosol parameters. Present satellite retrievals are limited, however, mainly to estimation of the aerosol optical thickness, which corresponds to the column total cross section of aerosol particles, from one or two channels of polar orbiters, for example, the National Oceanic and Atmospheric Administration’s (NOAA) Advanced Very High Resolution Radiometer (AVHRR

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