An Integrated Assessment of Basal Scattering and Topographic Roughness Information Derived from Greenland Radar-Sounding Data

Quantifying the basal roughness of ice sheets is important for understanding and constraining the role of basal traction on ice dynamics. Numerical model simulations demonstrate high sensitivity to the parametrisation of the lower boundary condition, which is governed by both basal roughness and the thermal state of the bed. In terms of ice dynamics history, basal roughness can reveal aspects of past behaviour as well as provide insight towards more recent flow distribution of marine sediments. Basal roughness information, defined here in general terms as the irregularity of the basal interface relative to a reference surface, can be obtained from radar-sounding data in two physically different ways. Firstly, via the statistical properties of along-track topography (e.g. from spectral analysis); and secondly via the electromagnetic scattering properties of the radar pulse (e.g. by quantifying the spread of the distribution of scattered energy). In general, the basal roughness of the Greenland Ice Sheet has been little studied, and the vast increase in recent Operation Ice Bridge radar-sounding data presents an opportunity for comprehensive, quantitative ice-sheet-wide analysis. Here we present a synthesis of basal scattering and topographic based roughness information for the Greenland Ice Sheet, along with a comparison to present day numerical model output including ice velocity, basal traction, and basal temperature. One central topic which we address is the scale dependence of basal roughness information that is inferred from both analysis methods, and the relationship with basal sliding physics. Consideration of scale is important since basal sliding is primarily controlled by higher frequency roughness. The other topic that we consider is identifying whether there are any defined and unambiguous roughness characteristics in regions where there is suspected to be a thawed basal interface. An overall goal of this work is to integrate basal roughness information with other radar-sounding data to produce a basal melt map for the Greenland Ice Sheet.