Regional-scale bed roughness beneath ice masses: measurement and analysis

We outline a method of assessing the roughness of the bed beneath ice-masses, applicable to data collected in a wide variety of (glaciated) environments. Roughness at scales > 10(2) m in particular is poorly constrained and understood in glaciated systems, and regional geophysical surveys collected over the past 30 years are ideally suited to addressing this issue. We demonstrate the technique using a radio-echo sounding data set collected during the 1970s, showing that regional characterization of roughness over a wide range of wavelengths (1 to > 40 km) is possible using Fast Fourier Transforms, even with quite coarse horizontal sampling. Coarse sampling captures all of the variation of higher resolution analyses and the technique appears robust up to the limit imposed by the Nyquist frequency. (C) 2004 Elsevier Ltd. All rights reserved.