The location of the transition where the ice resting on bedrock detaches and becomes a floating ice shelf is a critical parameter needed for calculations of the ice sheet mass budget, as well as for modelling ice ocean interactions, ice sheet dynamics, subglacial melt and oceanic tides. Due to its importance the grounding line position is one of the key parameters of the ice sheets which have been derived from satellite observations within the project.
The retrieval of the grounding line position is based on the influence of the ocean tides on the floating part of the ice which rests in hydrostatic equilibrium. Due to the fact that this tidal rise is absent on the grounded part of the glacier, a vertical deformation appears in the transition area.
The InSAR double differencing method (DInSAR) has been identified to be one of the most accurate techniques for locating the vertical tidal deformation of the ice sheet. At least two pairs of coherent repeat pass data sets must be combined in order to remove the common velocity component revealing the vertical component due to tidal motion. In practice the major limiting factor of this technique is the availability of datasets with sufficiently high InSAR coherence. Physical phenomena such as snow accumulation, drift, or melting may significantly change the surface properties between the satellite passes and thus the backscatter behaviour which can lead to loss of phase coherence in the interferograms.
GLL products are provided on ENVEO CryoPortal: http://cryoportal.enveo.at/. Access to product downloads requires registration and login. There are different user levels (anonymous, external, partner & staff) that determine the permissions for reading and accessing the data.