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| Titel |
The direct fitting approach for total ozone column retrievals: a sensitivity study on GOME-2/MetOp-A measurements |
| VerfasserIn |
A. Wassmann, T. Borsdorff, J. M. J. Brugh, O. P. Hasekamp, I. Aben, J. Landgraf |
| 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. 10 ; Nr. 8, no. 10 (2015-10-21), S.4429-4451 |
| Datensatznummer |
250116647
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| Publikation (Nr.) |
 copernicus.org/amt-8-4429-2015.pdf |
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| Zusammenfassung |
| We present a sensitivity study of the direct fitting approach to retrieve total ozone columns from the clear sky
Global Ozone Monitoring Experiment 2/MetOp-A (GOME-2/MetOp-A) measurements between 325 and
335 nm in the period 2007–2010. The direct fitting of the measurement is based on adjusting the
scaling of a reference ozone profile and requires accurate simulation of
GOME-2 radiances. In this context, we study the effect of three aspects that
introduce forward model errors if not addressed appropriately: (1) the use of
a clear sky model atmosphere in the radiative transfer demanding cloud
filtering, (2) different approximations of Earth's sphericity to address the
influence of the solar zenith angle, and (3) the need of polarization in
radiative transfer modeling. We conclude that cloud filtering using the
operational GOME-2 FRESCO (Fast Retrieval Scheme for Clouds from the Oxygen A band) cloud product, which is part of level 1B data, and
the use of pseudo-spherical scalar radiative transfer is fully sufficient for
the purpose of this retrieval. A validation with ground-based measurements at
36 stations confirms this showing a global mean bias of −0.1 % with a
standard deviation (SD) of 2.7 %. The regularization effect inherent to the
profile scaling approach is thoroughly characterized by the total column
averaging kernel for each individual retrieval. It characterizes the effect
of the particular choice of the ozone profile to be scaled by the inversion
and is part of the retrieval product. Two different interpretations of the
data product are possible: first, regarding the retrieval product as an
estimate of the true column, a direct comparison of the retrieved column with
total ozone columns from ground-based measurements can be done. This requires
accurate a priori knowledge of the reference ozone profile and the column
averaging kernel is not needed. Alternatively, the retrieval product can be
interpreted as an effective column defined by the total column averaging
kernel. This interpretation relies much less on the a priori knowledge of the
reference ozone profile; however, for its validation, measurements of the vertical
ozone distribution are needed. The different manners of data interpretation
are demonstrated for simulated and real measurements using on-ground ozone
column and ozonesonde measurements for validation. |
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