Bed topography and stickiness inferred from surface measurements on ice streams

Throstur Thorsteinsson*, R. Bindschadler||, G. H. Gu­mundsson# and C. F. Raymond*
* Geophysics Program, University of Washington, Seattle, WA 98195, USA
|| NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
# VAW-ETH Zentrum, Gloriastrasse 37/39, CH-8092, Zurich, Switzerland

Introduction. We attempt to relate observations of surface elevation, S, and velocities, U, V and W, to bed topography, B, and stickiness, C, at the bed, using transfer functions (e.g. Gu­mundsson et al. [1998]). Using synthetic data we have shown that our techniques can separate the effects of B and C, even with added white noise, when S and both components of horizontal velocity (U,V) are given.  This is easily satisfied using synthetic data, but becomes tricky when using real data.  We have looked at small scale (~1 km) features in topography on the surface of ice streams D and E, and used that information to invert for the bed topography, B, or basal stickiness, C.  One would like to determine both the bed topography and basal stickiness using information measured at the surface.  Since we only have good surface elevation data, we have assumed two end member cases, that there is only B or C at the bed.  In order to partition correctly between the effects of B and C we need S and (U,V). So far the (U,V) data has been irregularly spaced, which makes it impractical for inversion.  This study has shown that with surface and velocity data at about 0.25 km spacing  we can distinguish between the effects of bed topography and stickiness and resolve structures as small as 0.5 km.

I want to see the whole thing !
27 jan. 2003
© Þrõstur Þ.