"However, there are several areas where data are currently lacking such as along parts of the central and north east- ern margins of the ice sheet (Fig. S1). While the interior of Greenland is relatively smooth, there are still many ar- eas where the distance to the closest observation is more than 50 km, resulting in uncertainties in bed elevation ex- ceeding +/-100 m and missing potential short wavelength re- lief that is evident, for example, inland from Jakobshavn Is- brae (Fig. 5a)."
"Bathymetry seaward of the glaciers and beneath ice shelves is currently poorly characterised in some areas and non-existent in most."
For the purposes of comparing two elevations near each other as in a contour map, we are more interested in relative error between adjacent points, which i think could be smaller. Nevertheless, 50-100m is a good place to start as an error estimate. The map of flightlines in the supplementary materials is very instructive as well, the data in the areas covered is more reliable.
The paper is at
The Cryosphere, 7, 499-510, 2013 www.the-cryosphere.net/7/499/2013/ doi:10.5194/tc-7-499-2013
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