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189991 
Journal Article 
Testing the MODIS satellite retrieval of aerosol fine-mode fraction 
Anderson, T; Wu, Y; Chu, D; Schmid, B; Redemann, J; Dubovik, O 
2005 
Yes 
Journal of Geophysical Research
ISSN: 0148-0227
EISSN: 2156-2202 
110 
D18 
D18204 
Satellite retrievals of the fine-mode fraction (FMF) of
midvisible aerosol optical depth, tau, 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 tau. 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 angstrom
ngstrorm exponent, (a) over circle, 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 (a) over
circle 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 (a) over circle
since an excellent validation program is in place for doing this, and (2) suborbital measurements
should be used to derive relationships between a and fine-mode partitioning to allow
interpretation of the satellite data in terms of fine-mode aerosol optical depth.