The Cryosphere Discuss., 7, 873-920, 2013
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This discussion paper has been under review for the journal The Cryosphere (TC). Please refer to the corresponding final paper in TC.
An iterative inverse method to estimate basal topography and initialize ice flow models
W. J. J. van Pelt1, J. Oerlemans1, C. H. Reijmer1, R. Pettersson2, V. A. Pohjola2, E. Isaksson3, and D. Divine3
1Institute for Marine and Atmospheric research, Utrecht University, Utrecht, the Netherlands
2Department of Earth Sciences, Uppsala University, Uppsala, Sweden
3Norwegian Polar Institute, Tromsø, Norway

Abstract. We present and evaluate an inverse approach to reconstruct two-dimensional fields of bedrock topography and simultaneously initialize an ice flow model. The inverse method involves an iterative procedure in which an ice dynamical model (PISM) is run multiple times over a prescribed period, while being forced with space and time-dependent climate input. After every iteration bed heights are adjusted using information of the remaining misfit between observed and modeled surface topography. The inverse method is first applied in synthetic experiments with a constant climate forcing to verify convergence and robustness of the approach. In a next step, the inverse approach is applied to Nordenskiöldbreen, Svalbard, forced with height- and time-dependent climate input since 1300 AD. An L-curve stopping criterion is used to prevent overfitting. Validation against radar data reveals a high correlation (up to R = 0.89) between modeled and observed thicknesses. Remaining uncertainties can mainly be ascribed to inaccurate model physics, in particular uncertainty in the description of sliding. Results demonstrate the applicability of this inverse method to reconstruct the ice thickness distribution of glaciers and ice caps. In addition to reconstructing bedrock topography, the method provides a direct tool to initialize ice flow models for forecasting experiments. Application of the method is not constrained to a single model or glacier, indicating the potential to use the approach to compute the detailed thickness distribution of a single glacier, as well as the volume contained in a set of glaciers and ice caps.

Citation: van Pelt, W. J. J., Oerlemans, J., Reijmer, C. H., Pettersson, R., Pohjola, V. A., Isaksson, E., and Divine, D.: An iterative inverse method to estimate basal topography and initialize ice flow models, The Cryosphere Discuss., 7, 873-920, doi:10.5194/tcd-7-873-2013, 2013.
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