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| Titel |
Sensitivity analysis of polarimetric O2 A-band spectra for potential cloud retrievals using OCO-2/GOSAT measurements |
| VerfasserIn |
S. Sanghavi, M. Lebsock, G. Stephens |
| 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 ; 8, no. 9 ; Nr. 8, no. 9 (2015-09-07), S.3601-3616 |
| Datensatznummer |
250116568
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| Publikation (Nr.) |
 copernicus.org/amt-8-3601-2015.pdf |
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| Zusammenfassung |
Clouds play a crucial role in Earth's radiative budget, yet their climate
feedbacks are poorly understood. The advent of space-borne high resolution
spectrometers probing the O2 A band, like GOSAT and OCO-2, could make it
possible to simultaneously retrieve vertically resolved cloud parameters that
play a vital role in Earth's radiative budget, thereby allowing a
reduction of the corresponding uncertainty due to clouds. Such retrievals
would also facilitate air mass bias reduction in corresponding measurements of
CO2 columns.
In this work, the hyperspectral, polarimetric response of the O2 A band to
mainly three important cloud parameters, viz., optical thickness, top height
and droplet size has been studied, revealing a different sensitivity to each
for the varying atmospheric absorption strength within the A band. Cloud
optical thickness finds greatest sensitivity in intensity measurements, the
sensitivity of other Stokes parameters being limited to low cloud optical
thicknesses. Cloud height had a negligible effect on intensity measurements
at non-absorbing wavelengths but finds maximum sensitivity at an
intermediate absorption strength, which increases with cloud height. The same
is found to hold for cloud geometric thickness. The geometry-dependent
sensitivity to droplet size is maximum at non-absorbing wavelengths and
diminishes with increasing absorption strength. It has been shown that
significantly more information on droplet size can be drawn from multi-angle
measurements. We find that, in the absence of sunglint, the backscatter
hemisphere (scattering angle larger than 90°) is richer in information
on droplet size, especially in the glory and rainbow regions. It has been
shown that I and Q generally have differing sensitivities to all cloud
parameters. Thus, accurate measurements of two orthogonal components
IP andIS (as in GOSAT) are expected to contain more
information than measurements of only I, Ih or Iv
(as in the case of OCO-2). |
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