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| Titel |
Testing aerosol properties in MODIS Collection 4 and 5 using airborne sunphotometer observations in INTEX-B/MILAGRO |
| VerfasserIn |
J. Redemann, Q. Zhang, J. Livingston, P. Russell, Y. Shinozuka, A. Clarke, R. Johnson, R. Levy |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 9, no. 21 ; Nr. 9, no. 21 (2009-11-02), S.8159-8172 |
| Datensatznummer |
250007717
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| Publikation (Nr.) |
 copernicus.org/acp-9-8159-2009.pdf |
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| Zusammenfassung |
| The 14-channel Ames Airborne Tracking Sunphotometer (AATS) was operated on a
Jetstream 31 (J31) aircraft in March 2006 during MILAGRO/INTEX-B (Megacity
Initiative-Local And Global Research Observations/Phase B of the
Intercontinental Chemical Transport Experiment). We compare AATS retrievals
of spectral aerosol optical depth (AOD) and related aerosol properties with
corresponding spatially coincident and temporally near-coincident
measurements acquired by the MODIS-Aqua and MODIS-Terra satellite sensors.
These comparisons are carried out for the older MODIS Collection 4 (C4) and
the new Collection 5 (C5) data set, the latter representing a reprocessing
of the entire MODIS data set completed during 2006 with updated calibration
and aerosol retrieval algorithm. Our analysis yields a direct, validated
assessment of the differences between select MODIS C4 and C5 aerosol
retrievals. Our analyses of 37 coincident observations by AATS and
MODIS-Terra and 18 coincident observations between AATS and MODIS-Aqua
indicate notable differences between MODIS C4 and C5 and between the two
sensors. For MODIS-Terra, we find an average increase in AOD of 0.02 at 553 nm
and 0.01 or less at the shortwave infrared (SWIR) wavelengths. The change
from C4 to C5 results in less good agreement with the AATS derived spectral
AOD, with average differences at 553 nm increasing from 0.03 to 0.05. For
MODIS-Aqua, we find an average increase in AOD of 0.008 at 553 nm, but an
increase of nearly 0.02 at the SWIR wavelengths. The change from C4 to C5
results in slightly less good agreement to the AATS derived visible AOD,
with average differences at 553 nm increasing from 0.03 to 0.04. However, at
SWIR wavelengths, the changes from C4 to C5 result in improved agreement
between MODIS-Aqua and AATS, with the average differences at 2119 nm
decreasing from −0.02 to −0.003. Comparing the Angstrom exponents calculated
from AOD at 553nm and 855nm, we find an increased rms difference from AATS
derived Angstrom exponents in going from C4 to C5 for MODIS-Terra, and a
decrease in rms difference, hence an improvement, for the transition from C4
to C5 in MODIS-Aqua. Combining the AATS retrievals with in situ measurements
of size-dependent aerosol extinction, we derive a suborbital measure of the
aerosol submicron fraction (SMF) of AOD and compare it to MODIS retrievals
of aerosol fine mode fraction (FMF). Our analysis shows a significant
rms-difference between the MODIS-Terra FMF and suborbitally-derived SMF of
0.17 for both C4 and C5. For MODIS-Aqua, there is a slight improvement in
the transition from C4 to C5, with the rms-difference from AATS dropping
from 0.23 to 0.16. The differences in MODIS C4 and C5 AOD in this limited
data set can be traced to changes in the reflectances input to the aerosol
retrievals. An extension of the C4-C5 comparisons from the area along the
J31 flight track to a larger study region between 18–23° N and 93–100° W
on each of the J31 flight days supports the finding of significant
differences between MODIS C4 and C5. |
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