Elevation change and remote-sensing mass-balance methods on the Greenland ice sheet

The mass balance of the Greenland Ice Sheet is virtually impossible to obtain with traditional ground-based methods alone due to its vast size. It is thus desirable to develop mass-balance methods depending on remote sensing instead and this field has experienced a dramatic development within the last decade.

Large amounts of data have been collected from satellite and airborne platforms, yielding surface elevation changes and surface velocity fields. Here we present data from the Greenland Ice-Sheet margin acquired with a new small-scale airborne system, designed for regional high-density coverage. During campaigns in 2000, 2003 and 2005, we have collected and processed ice-sheet surface elevation and ice-thickness data, acquired with a laser altimeter and a 60~MHz ice-penetrating radar.

Both instruments were mounted on a small Twin-Otter aircraft which were positioned using three onboard differential GPS instruments and corrected for pitch, roll and crab using an Inertial Navigation System. Knowledge of elevation change and ice thickness alone does not provide mass balance, but when combined with the surface velocity field obtained from satellite repeat-track interferometric synthetic aperture radar (InSAR), it is possible to apply the principle of mass conservation and derive the mass balance from this.

The method has previously been applied to a flow line, but the intention is here to attempt a regional, distributed calculation. We will present the method and its weaknesses and show a map of measured surface elevation change over a 50x50~km part of the western Greenland Ice-Sheet margin near Kangerlussuaq.

In this region, the mean observed elevation change has been -0.5~m from 2000 to 2003. However, the change is unevenly distributed with the northern and central part generally in balance and the southern part clearly thinning.