Internal layers in radio-echograms from the sounding of ice sheets have long been a valuable resource in glaciology, but their usefulness have been limited by availability of traced (digitized) layers. To speed up this process, we have developed an algorithm for semi-automatic tracing the internal layers and a fully automated algorithm for mapping the layer slope. The layer slope is inferred by the intensity response to a slanted Gaussian filter, whereafter layers can be traced using an active contour model. With these techniques we show that it possible to trace internal layers over distances of hundreds kilometers with minimal operator intervention, and the methods have been successfully validated between two Greenland deep ice cores with internal match points. In order to remove any operator assistance, we show how the layer slope can be used to detect disturbances in the deep radiostratigraphy of the Greenland Ice Sheet. We find that the disturbances are scattered over the northern part of the ice sheet, with the highest density upstream from the Petermann glacier. The disturbances does not seem to be correlated with surface velocities and can be found on, and close, to the ice divide. These results highlight the viability of using internal layer slopes to answer glaciological questions, and the need for high resolution mapping of the interior ice sheet to understand the dynamical nature of the basal environment.
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The Niels Bohr Institute, Faculty of Science, University of Copenhagen, 2015