Calculation of ice velocities in the Jakobshavn Isbrae area using airbornelaser altimetry

The ability to measure velocities of fast-moving glaciers is essential to t he understanding and interpretation of their dynamics and related processes . This is especially important in the Jakobshavn drainage basin of the Gree nland ice sheet, where a significant portion of the ice sheet mass loss occ urs and the iceberg calving rate is high. In this article, zee present a me thod for using airborne laser altimetry data to determine surface velocitie s in portions of the Jakobshavn drainage basin that have distinct elevation features. By examining correlations between repeat elevation surveys, the motion of these features, the most distinct of which are crevasses, is trac ked. Results show that for areas with a standard deviation in elevation in excess of 1 m, displacement of features can be tracked to a precision of 1- 2 m, and the corresponding velocities can be retrieved. The maximum velocit y of the Jakobshavn Isbrae, at its calving front, is found to be nearly 7 k m yr(-1). Ice stream boundaries and flow patterns can also be observed in t he derived velocity data. (C)Elsevier Science Inc., 1999.