Jökull - 01.01.2012, Page 138

E. Magnússon et al.
Figure 4. a) An example of a RES profile
within the Öræfajökull caldera. b) The same
profile with interpreted bedrock backscat-
ter (red lines). c) Corresponding profile
locations. Roman numbers in a and b
show matching locations. – a) Dæmi um
íssjármælisnið innan Öræfajökulsöskjunnar.
b) Staðsetning sniðsins. b) Sama snið með
túlkuðu botnendurkasti (rauð lína). c) Stað-
setning sniðsins. Rómverskar tölur á b sam-
svara punktum á a.
glaciated areas rather simple in most cases. In more
complex areas where this method was not sufficient,
an ortho-rectified SPOT5 image from September 2010
was used to further aid the interpretation. The inter-
preted outlines were then used to extract the elevation
at the glacier margin from the LiDAR DEM to se-
cure continuity between the DEMs of the subglacial
bedrock and the ice free regions.
In some regions of Öræfajökull the RES data are
sparse or completely absent. This is particularly true
in steep and crevassed regions where RES measure-
ments would be both risky and time consuming. To
compensate for lack of observations in these regions
we use the RES data from 2009 to estimate a rela-
tion between the ice thickness and the surface slope
θ calculated from degraded LiDAR DEM with 100
136 JÖKULL No. 62, 2012