Applied geophysics in glaciology: Can we save models?

The flow of ice sheets is controlled by processes occurring at their surface, base and by the spatial variation of rheological properties within the ice. The internal structure of ice sheets represents an integrated memory of the interaction of these processes and properties, knowledge of which has key implications for unraveling history and predicting future behaviour. Numerical models are routinely employed to understand and reproduce the flow of ice. However, models rely on a number of simplyfing assumptions. Despite - partly also because of - the increasing sophistication of ice-flow models over recent years, in-situ observations are still necessary to reduce the number and fix values of free model parameters controlling flow. Yet, the degree of data incorporation in ice-flow models is not as advanced as for example in oceanography or meteorology.The most direct way to obtain in-situ properties within the ice is drilling ice cores. However, this is a labour intensive task, which only provides information for a single point, albeit in very high resolution. Active geophysical methods, in contrast, are employed from above the ice surface, allowing to cover larger areas in a comparably short amount of time. Laterally imaging the layer architecture of ice sheets yields complementary information to model results or the direct evidence of physical properties otherwise solely provided by ice cores.This talk gives an overview of the state of the art of active seismic and electromagnetic reflection methods in glaciology. It is shown how these methods provide insights into the distribution of physical properties, stratigraphy, structure and subglacial conditions. An emphasis is put on the role of crystal orientation fabrics (COF) for ice flow and active geophysics alike. Pinning down the distribution of COF is an example how flow modeling and geophysics should be fruitfully combined for a mutual benefit and how this could finally lead to data assimilation in ice-flow models