Reconstruction of basal properties in ice sheets using iterative inverse methods

Published: Sep 1, 2012 by The PISM Authors


Title	Reconstruction of basal properties in ice sheets using iterative inverse methods
Authors	Marijke Habermannand others
Venue	Journal of Glaciology

Inverse methods are used to estimate model parameters from observations, here basal shear stress from the surface velocity of an ice sheet. One starts with an initial estimate of the model parameters and then updates them to improve the match to observations in an iterative process. Large-scale spatial features are adjusted first. A stopping criterion prevents the overfitting of data. In this paper, iterative inverse methods are applied to the shallow-shelf approximation forward model. A new incomplete Gauss–Newton method is introduced and compared to the steepest descent and nonlinear conjugate gradient methods. Two different stopping criteria, the discrepancy principle and a recent-improvement threshold, are compared. The IGN method shows faster convergence than the others. Though PISM is not mentioned by this paper, and the experiments were done in python, code supporting these inversion methods is already present in the PISM dev branch.

A two-year PostDoc positions in ice sheet and Earth system modelling is available in the Ice Dynamics group, as part of the new Earth Resilience Science Unit (ERSU), at the Potsdam Institute for Climate Impact Research (PIK).

Two PhD fellowship positions in ice sheet modelling are advertised at the Niels Bohr Institute, University of Copenhagen.

The Alfred Wegener Institute, Bremerhaven, is offering a PhD position in the field of coupled ice sheet-ocean modelling. The core of the project is to run simulations with FESOM-PISM (a coupled ocean-ice shelf-ice sheet model with evolving cavity geometries) for different 21st-century climate projections to obtain well-constrained trajectories of future ice mass loss from the vast Antarctic Ice Sheet. Model results will feed into a fingerprinting method that considers the ocean response as well as gravitational effects and contributions from other sources. The final product will be a time series of global maps of regional sea-level variations that consider all of the most relevant processes.