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| Titel |
Retrieval of the optical depth and vertical distribution of particulate scatterers in the atmosphere using O2 A- and B-band SCIAMACHY observations over Kanpur: a case study |
| VerfasserIn |
S. Sanghavi, J. V. Martonchik, J. Landgraf, U. Platt |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 5, no. 5 ; Nr. 5, no. 5 (2012-05-16), S.1099-1119 |
| Datensatznummer |
250002867
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| Publikation (Nr.) |
 copernicus.org/amt-5-1099-2012.pdf |
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| Zusammenfassung |
Due to the well-defined vertical profile of O2 in the atmosphere, the
strong A-band (757–774 nm) has long been used to estimate vertical
distributions of aerosol/cloud from space. We extend this approach to include
part of the O2 B-band (684–688 nm) as well. SCIAMACHY onboard ENVISAT
is the first instrument to provide spectral data at moderate resolution
(0.2–1.5 nm) in the UV/VIS/NIR including both the O2 A- and B-bands.
Using SCIAMACHY specifications, we make combined use of these bands in an
optimal estimation algorithm. Theoretical studies show that our algorithm is
applicable both over bright and dark surfaces for the retrieval of a
lognormal approximation of the vertical profile of particulate matter, in
addition to its optical thickness. Synthetic studies and information content
analyses prove that such a combined use provides additional information on
the vertical distribution of atmospheric scatterers, attributable to
differences in the absorption strengths of the two bands and their underlying
surface albedos.
Due to the high computational cost of the retrieval, we restrict application
to real data to a case study over Kanpur through the year 2003. Comparison
with AERONET data shows a commonly observed seasonal pattern of haziness,
manifesting a correlation coefficient of r = 0.92 for non-monsoon monthly
mean AOTs. The retrieved particulate optical thickness is found to be
anti-correlated with the relative contrast of the Lambertian equivalent
reflectivity (LER) at 682 nm and 755 nm by a coefficient of 0.788,
confirming the hypothesis made in Sanghavi et al. (2010).
Our case study demonstrates a stable physics-based retrieval of particulate
matter using only SCIAMACHY data. The feasibility of our approach is enhanced
by the information provided by measurements around the O2 B-band in
addition to the A-band. Nonetheless, operational application to SCIAMACHY
data remains challenged by radiometric uncertainties, yielding simultaneous
retrieval of particle microphysical parameters impracticable and leading to
over-reliance on climatological data. Addressing these issues in future
instruments similar to SCIAMACHY, coupled with computational resources and
speed-up of the current line-by-line radiative transfer calculations, can
allow our approach to be extended to the global scale, particularly as it is
not limited to dark surfaces. |
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