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JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 110,
D18204,
doi:10.1029/2005JD005978,
2005
Testing the MODIS satellite retrieval of aerosol fine-mode fraction
Theodore L. Anderson
Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA
Yonghua Wu
Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA
D. Allen Chu
Joint Center for Earth Systems Technology, University of Maryland, Baltimore, Maryland, USA Laboratory for Atmospheres, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Beat Schmid
Bay Area Environmental Research Institute, Sonoma, California, USA
Jens Redemann
Bay Area Environmental Research Institute, Sonoma, California, USA
Oleg Dubovik
Goddard Earth Sciences and Technology Center, University of Maryland, Greenbelt, Maryland, USA Laboratory for Terrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Abstract
Satellite retrievals of the fine-mode fraction (FMF) of midvisible aerosol optical depth, τ, are potentially valuable for
constraining chemical transport models and for assessing the global distribution of anthropogenic aerosols. Here we compare
satellite retrievals of FMF from the Moderate Resolution Imaging Spectroradiometer (MODIS) to suborbital data on the submicrometer
fraction (SMF) of τ. SMF is a closely related parameter that is directly measurable by in situ techniques. The primary suborbital
method uses in situ profiling of SMF combined with airborne Sun photometry both to validate the in situ estimate of ambient
extinction and to take into account the aerosol above the highest flight level. This method is independent of the satellite
retrieval and has well-known accuracy but entails considerable logistical and technical difficulties. An alternate method
uses Sun photometer measurements near the surface and an empirical relation between SMF and the Ångström exponent, å, a measure
of the wavelength dependence of optical depth or extinction. Eleven primary and fifteen alternate comparisons are examined
involving varying mixtures of dust, sea salt, and pollution in the vicinity of Korea and Japan. MODIS ocean retrievals of
FMF are shown to be systematically higher than suborbital estimates of SMF by about 0.2. The most significant cause of this
discrepancy involves the relationship between å and fine-mode partitioning; in situ measurements indicate a systematically
different relationship from what is assumed in the satellite retrievals. Based on these findings, we recommend: (1) satellite
programs should concentrate on retrieving and validating å since an excellent validation program is in place for doing this,
and (2) suborbital measurements should be used to derive relationships between å and fine-mode partitioning to allow interpretation
of the satellite data in terms of fine-mode aerosol optical depth.
Received 15
March
2005;
accepted 30
June
2005;
published 22
September
2005.
Keywords: fine-mode aerosol;
satellite retrieval;
satellite validation;
ACE-Asia.
Index Terms: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801, 4906); 0360 Atmospheric Composition and Structure: Radiation: transmission and scattering; 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry; 0394 Atmospheric Composition and Structure: Instruments and techniques; 3360 Atmospheric Processes: Remote sensing.
Read Full Article (file size: 1053897 bytes) Cited by
Citation: Anderson, T. L., Y. Wu, D. A. Chu, B. Schmid, J. Redemann, and O. Dubovik
(2005),
Testing the MODIS satellite retrieval of aerosol fine-mode fraction,
J. Geophys. Res.,
110,
D18204,
doi:10.1029/2005JD005978.
Copyright 2005 by the American Geophysical Union.
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