The airborne and ground-based radar sounding of gaciers and ice sheets is a well-established technique which images the thickness and internal structure of ice. Whenever the emitted pulse encounters a boundary in dielectric properties, it is partly reflected and partly transmitted. While the ice-bedrock interface typically exhibits the largest dielectric contrast, weaker internal variations may also be caused by a changing density, electrical conductivity or crystal orientation. In case those internal variations are coherent in the horizontal they appear as internal reflections horizons in the radar data. Under the assumption that the dielectric properties of the individual layers are originally linked to depositional events on the former surface (e.g. large scale deposition of volcanic fallout), the internal layers can be considered to be isochrones. As such, they offer a formidable tool to link ice cores, validate ice-flow models, but also to derive glaciological parameters like the spatial variation of accumulation or the conditions at the ice-bedrock interface (wet or dry).
Start the video at the top to see an example of a airborne radar profiles collected across a coastal ice rise (Halvfarryggen) in Dronning Maud Land Antarctica. The excerpt shown is roughly 60×60 km. The video starts with a 3D representation of the surface topography. The three ice divides (which merge in a triple junction near the dome) are marked with blue lines, the radar cross sections with green lines. Below the surface, the strongest reflector originates from the bedrock interface. Between the surface and the bedrock, many internal reflection horizons are apparent. The layering bends upwards characteristically beneath the divides. This feature can be related to the non-linear and generally quite complex rheology of ice. The upward-bending is known as the Raymond effect. Data for this example was collected by Daniel Steinhage (AWI) in conjunction with the LIMPICS campaign to Antarctica in 2009/2010.