Ice velocity measurements of Langjökull, Iceland, from interferometric synthetic aperture radar (InSAR)

We have computed the velocity of Langjökull ice cap (LIC), Iceland, using InSAR data acquired by the European Remote-sensing Satellite in 1994 and an ice-surface elevation model derived from a GPS survey conducted in 1997. The velocity map covers 68% of the 925 km² of LIC. Eight principal outlet glaciers were identified, along which ice velocities increased from zero at the ice divide to a maximum of 75 ma^-1. When the InSAR velocity dataset is compared with surface GPS measurements of ice flow determined in summer 2001, there is generally good agreement, suggesting interannual and seasonal stability for much of the ice cap during this period. However, non-zero ice velocities at the termini of four of the eight glaciers surveyed suggest that these glaciers were advancing in 1994. Comparison of our GPS and InSAR velocities suggests that Sudurjókull experienced elevated velocity in late February 1994, which, when other studies are considered, appears to be consistent with a glacier surge.