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| Titel |
Assimilation of ASCAT near-surface soil moisture into the SIM hydrological model over France |
| VerfasserIn |
C. Draper, J.-F. Mahfouf, J.-C. Calvet, E. Martin, W. Wagner |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 15, no. 12 ; Nr. 15, no. 12 (2011-12-21), S.3829-3841 |
| Datensatznummer |
250013059
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| Publikation (Nr.) |
 copernicus.org/hess-15-3829-2011.pdf |
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| Zusammenfassung |
| This study examines whether the assimilation of remotely sensed near-surface
soil moisture observations might benefit an operational hydrological model,
specifically Météo-France's SAFRAN-ISBA-MODCOU (SIM) model. Soil moisture data
derived from ASCAT backscatter observations are assimilated into SIM using a
Simplified Extended Kalman Filter (SEKF) over 3.5 years. The benefit of the
assimilation is tested by comparison to a delayed cut-off version of SIM, in
which the land surface is forced with more accurate atmospheric analyses, due
to the availability of additional atmospheric observations after the
near-real time data cut-off. However, comparing the near-real time and
delayed cut-off SIM models revealed that the main difference between them is
a dry bias in the near-real time precipitation forcing, which resulted in a
dry bias in the root-zone soil moisture and associated surface moisture flux
forecasts. While assimilating the ASCAT data did reduce the root-zone soil
moisture dry bias (by nearly 50%), this was more likely due to a bias within
the SEKF, than due to the assimilation having accurately responded to the
precipitation errors. Several improvements to the assimilation are identified
to address this, and a bias-aware strategy is suggested for explicitly
correcting the model bias. However, in this experiment the moisture added by
the SEKF was quickly lost from the model surface due to the enhanced surface
fluxes (particularly drainage) induced by the wetter soil moisture states.
Consequently, by the end of each winter, during which frozen conditions
prevent the ASCAT data from being assimilated, the model land surface had
returned to its original (dry-biased) climate. This highlights that it would
be more effective to address the precipitation bias directly, than to correct
it by constraining the model soil moisture through data assimilation. |
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