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| Titel |
Validation of GOMOS ozone precision estimates in the stratosphere |
| VerfasserIn |
V. F. Sofieva, J. Tamminen, E. Kyrölä, A. Laeng, T. Clarmann, F. Dalaudier, A. Hauchecorne, J.-L. Bertaux, G. Barrot, L. Blanot, D. Fussen, F. Vanhellemont |
| 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 ; 7, no. 7 ; Nr. 7, no. 7 (2014-07-16), S.2147-2158 |
| Datensatznummer |
250115849
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| Publikation (Nr.) |
 copernicus.org/amt-7-2147-2014.pdf |
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| Zusammenfassung |
Accurate information about uncertainties is required in nearly all data
analyses, e.g., inter-comparisons, data assimilation, combined use.
Validation of precision estimates (viz., the random component of estimated
uncertainty) is important for remote sensing measurements, which provide the
information about atmospheric parameters by solving an inverse problem. For
the Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument, this
is a real challenge, due to the dependence of the signal-to-noise ratio (and
thus precision estimates) on stellar properties, small number of
self-collocated measurements, and growing noise as a function of time due to
instrument aging. The estimated ozone uncertainties are small in the
stratosphere for bright star occultations, which complicates validation of
precision values, given the natural ozone variability.
In this paper, we discuss different methods for geophysical validation of
precision estimates and their applicability to GOMOS data. We propose a
simple method for validation of GOMOS precision estimates for ozone in the
stratosphere. This method is based on comparisons of differences in sample
variance with differences in uncertainty estimates for measurements from
different stars selected in a region of small natural variability.
For GOMOS, the difference in sample variances for different stars at tangent
altitudes 25–45 km is well explained by the difference in squared
precisions, if the stars are not dim. Since this is observed for several
stars, and since normalized χ2 is close to 1 for these occultations
in the stratosphere, we conclude that the GOMOS precision estimates are
realistic in occultations of sufficiently bright stars. For dim stars,
errors are overestimated due to improper accounting of the dark charge correction
uncertainty in the error budget. The proposed method can also be applied to
stratospheric ozone data from other instruments, including multi-instrument
analyses. |
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