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| Titel |
Validation of GOME-2/MetOp-A total water vapour column using reference radiosonde data from the GRUAN network |
| VerfasserIn |
M. Antón, D. Loyola, R. Román, H. Vömel |
| 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. 3 ; Nr. 8, no. 3 (2015-03-06), S.1135-1145 |
| Datensatznummer |
250116205
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| Publikation (Nr.) |
 copernicus.org/amt-8-1135-2015.pdf |
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| Zusammenfassung |
| The main goal of this paper is to validate the total water vapour column
(TWVC) measured by the Global Ozone Monitoring Experiment-2 (GOME-2)
satellite sensor and generated using the GOME Data Processor (GDP) retrieval
algorithm developed by the German Aerospace Centre (DLR). For this purpose,
spatially and temporally collocated TWVC data from highly accurate sounding
measurements for the period January 2009–May 2014 at six sites are used.
These balloon-borne data are provided by the GCOS Reference Upper-Air Network
(GRUAN). The correlation between GOME-2 and sounding TWVC data is reasonably
good (determination coefficient, R2, of 0.89) when all available
radiosondes (1400) are employed in the inter-comparison. When cloud-free
cases (544) are selected by means of the satellite cloud fraction
(CF < 5%), the correlation exhibits a remarkable improvement
(R2 ~ 0.95). Nevertheless, the analysis of the relative
differences between GOME-2 and GRUAN data shows a mean absolute bias error
(weighted with the combined uncertainty derived from the estimated errors of
both data sets) of 15% for all-sky conditions (9% for cloud-free
cases). These results evidence a notable bias in the satellite TWVC data
against the reference balloon-borne measurements, partially related to the
cloudy conditions during the satellite overpass. The detailed analysis of the
influence of cloud properties – CF, cloud top albedo (CTA) and cloud top
pressure (CTP) – on the satellite-sounding differences reveals, as expected, a
large effect of clouds in the GOME-2 TWVC data. For instance, the relative
differences exhibit a large negative dependence on CTA, varying from −6 to
−23% when CTA rises from 0.3 to 0.8. Furthermore, the
satellite-sounding TWVC differences show a strong dependence on the satellite
solar zenith angle (SZA) for values above 50°. Hence the smallest
relative differences found in this satellite-sounding comparison are achieved
for those cloud-free cases with satellite SZA below 50°. Finally, the
relative differences also show a negative dependence on the reference TWVC
values, e.g. changing from +10% (TWVC below 10 mm) to −10%
(TWVC above 40 mm) when cloud-free conditions with SZA below 50° are
selected. Overall, relative differences within ±10% with respect to
reference sounding data for a large range of TWVC values can be considered as
a good result for satellite retrievals. |
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