# Validation case studies¶

“Validation” describes the comparison of numerical model output with physical observations in cases where the observations are sufficiently-complete and of sufficient quality so that the performance of the numerical model can be assessed [151], [152]. Roughly speaking, validation can happen when the observations or data are better than the model, so the comparison measures the quality of the numerical model and not merely errors in, or incompleteness of, the data. Because of the difficulty of measuring boundary conditions for real ice flows, this situation is not automatic in glaciology, or even common.1 Nonetheless we try two cases, first where PISM is applied on millimeter scale to model a laboratory experiment, and second for a large-scale ice flow in which all uncertainties of bedrock topography, basal sliding, and subglacial hydrology are removed, namely a present-day ice shelf.

Footnotes

- 1
Which explains the rise of “simplified geometry intercomparisons”; see section Simplified geometry experiments.

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