| Summary: | The basal roughness of glaciers and ice sheets is an important parameter controlling ice flow. Ice will generally slide faster over a smoother bed than a rougher one, but the horizontal scale of roughness is as important as its amplitude. Studies of basal roughness to date have used airborne radar data, which capture kilometer-scale roughness well, but for which it is challenging to resolve the smaller-scale roughness that is likely more important to ice flow. Here we present the results of a ground-based radar survey to study basal roughness on the scale of 10s to 100s of meters, and relate these observations to basal conditions. The data are from Thwaites Glacier, West Antarctica, one of the largest and fastest-flowing outlet glaciers on the continent, as well as one that is thinning rapidly and contributing to sea-level rise. We assess the value of different methods for quantitatively characterizing roughness using radar data, including bed-echo intensities, along-track root-mean-square (RMS) deviation of the basal topography, and spectral and wavelet analysis of the basal topography. We find that roughness is greater across-flow than along-flow, and greater downstream than upstream in our study area. This spatial organization results from a combination of pre-existing topography and glacial erosion. The multi-method analysis allows us to robustly characterize basal roughness in our study area. We correlate our results with existing models of greater basal shear stress downstream, and infer the presence of subglacial water. Finally, we clarify the nature of the relationship between basal conditions and roughness and relate our findings to those of similar studies.
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