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| Titel |
Adjoint accuracy for the full Stokes ice flow model: limits to the transmission of basal friction variability to the surface |
| VerfasserIn |
N. Martin, J. Monnier |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1994-0416
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| Digitales Dokument |
URL |
| Erschienen |
In: The Cryosphere ; 8, no. 2 ; Nr. 8, no. 2 (2014-04-24), S.721-741 |
| Datensatznummer |
250116097
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| Publikation (Nr.) |
 copernicus.org/tc-8-721-2014.pdf |
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| Zusammenfassung |
| This work focuses on the numerical assessment of the
accuracy of an adjoint-based gradient in the perspective of variational data
assimilation and parameter identification in glaciology. Using noisy
synthetic data, we quantify the ability to identify the friction coefficient
for such methods with a non-linear friction law. The exact adjoint problem is
solved, based on second-order numerical schemes, and a comparison with the
so-called "self-adjoint" approximation, neglecting the viscosity dependence
on the velocity (leading to an incorrect gradient), common in glaciology, is
carried out. For data with a noise of 1%, a lower bound of identifiable
wavelengths of 10 ice thicknesses in the friction coefficient is
established, when using the exact adjoint method, while the "self-adjoint"
method is limited, even for lower noise, to a minimum of 20 ice thickness
wavelengths. The second-order exact gradient method therefore provides
robustness and reliability for the parameter identification process. In
another respect, the derivation of the adjoint model using algorithmic
differentiation leads to the formulation of a generalization of the
"self-adjoint" approximation towards an incomplete adjoint method,
adjustable in precision and computational burden. |
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