Testing techniques to quantify drumlin height and volume: Synthetic DEMs as a diagnostic tool

Glacial bedform height (H) and volume (V) likely preserve important information about the behaviour of former ice sheets. However, large systematic errors exist in the measurement of H and V. Three semi-automated methods to isolate drumlins from other components of the landscape (e.g. trees, hills) as portrayed by NEXTMap have recently been devised; however, it is unclear which is most accurate. This paper undertakes the first quantitative comparison of such readily implementable methods, illustrating the use of statistically representative 'synthetic landscapes' as a diagnostic tool. From this analysis, guidelines for quantifying the 3D attributes of drumlins are proposed. Specifically, to avoid obtaining incorrect estimates caused by substantial systematic biases, interpreters should currently take three steps: declutter the digital elevation model for estimating H but not V; remove height data within the drumlin; then interpolate across the resultant hole to estimate a basal surface using Delaunay triangulation. Results are demonstrated through analysis of drumlins in an area in western central Scotland. The guidance arguably represents the best current advice for subglacial bedforms in general, highlighting the need for more studies into the quality of mapped data using synthetic landscapes.