Journal cover Journal topic
The Cryosphere An interactive open-access journal of the European Geosciences Union
doi:10.5194/tc-2016-283
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
10 Jan 2017
Review status
This discussion paper is under review for the journal The Cryosphere (TC).
Self-affine subglacial roughness: consequences for radar scattering and basal thaw discrimination in northern Greenland
Thomas M. Jordan1, Michael A. Cooper1, Dustin M. Schroeder2, Christopher N. Williams1, John D. Paden3, Martin J. Siegert4, and Jonathan L. Bamber1 1Bristol Glaciology Centre, School of Geographical Sciences, University of Bristol, Bristol, UK
2Department of Geophysics, Stanford University, Stanford, California, USA
3Center for Remote Sensing of Ice Sheets, University of Kansas, Lawrence, Kansas, USA
4Grantham Institute and Department of Earth Science and Engineering, Imperial College, London, UK
Abstract. Subglacial roughness can be determined at variety of length scales from radio-echo sounding (RES) data; either via statistical analysis of along-track topography, or inferred from basal radar scattering. Past studies have demonstrated that subglacial terrain exhibits self-affine (fractal) scaling behaviour, where vertical roughness has a power-law relationship with the horizontal length scale. A self-affine statistical framework, which enables a consistent integration of topographic roughness and radar scattering, has yet to be applied to RES. Here we do this for recent RES data from northern Greenland, and demonstrate that subglacial topography exhibits pronounced spatial variation in the Hurst (roughness power-law) exponent. A radar scattering model then enables us to explain how the Hurst exponent exerts strong topographic control upon radar scattering, which we map using the waveform abruptness (pulse peakiness) parameter. Notably, lower abruptness (associated with diffuse scattering) occurs for regions with a higher Hurst exponent, and higher abruptness (associated with specular reflections) occurs for regions with a lower Hurst exponent. Finally, we compare the RES-derived data with an independent prediction for the subglacial thermal state of northern Greenland. This analysis shows that the majority of predicted thawed regions do not have the specular RES scattering signature of deep subglacial lakes, and instead have a diffuse scattering signature.

Citation: Jordan, T. M., Cooper, M. A., Schroeder, D. M., Williams, C. N., Paden, J. D., Siegert, M. J., and Bamber, J. L.: Self-affine subglacial roughness: consequences for radar scattering and basal thaw discrimination in northern Greenland, The Cryosphere Discuss., doi:10.5194/tc-2016-283, in review, 2017.
Thomas M. Jordan et al.
Thomas M. Jordan et al.
Thomas M. Jordan et al.

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Short summary
Using radar-sounding data from northern Greenland, we demonstrate that basal radar scattering is strongly controlled by topography. Via comparison with a prediction for the basal thermal state we show that thawed regions generally exhibit diffuse scattering (rather than the specular signature associated with subglacial lakes). This has important consequences for basal thaw discrimination from radar-sounding, and hence in deriving non-ambiguous information for application in ice sheet models.
Using radar-sounding data from northern Greenland, we demonstrate that basal radar scattering is...
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