Analysis of the Motion Behaviour of Jakobshavn Isbræ Glacier in Greenland by Monocular Image Sequence Analysis

Jakobshavn Isbræ on the west coast of Greenland is one of the fastest and most productive glaciers in the world. It has been moving with an average velocity of 20 meters per day over a long time, producing to total annual iceberg volume of 30 40 km. In recent years a dramatic retreat of the glacier front has been observed. At the same time, a significant increase of the moving velocity has been reported. In summer 2004, a terrestrial photogrammetric measurement campaign has been conducted at this UNESCO world natural heritage site with the goal of determining precise spatio-temporal velocity fields at the tongue of Jakobshavn Isbræ glacier from high resolution digital camera image sequences. The characteristics of the glacier movement suggest a primarily one-dimensional motion field, possibly superimposed by tideinduced height changes. The velocity component perpendicular to the general flow direction of the glacier can be considered negligible. Therefore terrestrial monocular image sequences, recorded by a high resolution stillvideo camera, were processed to analyze the motion behavior of the glacier. Trajectories describing the glacier motion were determined by adapted image matching techniques based on the natural surface texture of the glacier. A scale factor for each image space trajectory was derived from a geodetic-photogrammetric network. From these image sequences, transformed into object space, the daily motion rate of glacier surface structures could be determined at a precision of a few centimeters over a field of view of approximately 2x2 square kilometers. The results obtained from processing image sequences recorded over 12-36 hours show daily motion rates of 40 meter per day and a clear correlation of the height component with the tidal curve. This indicates that the glacier tongue is floating on the fjord. The results of the photogrammetric measurements form a valuable basis for glaciological research on the changing behavior of Jakobshavn Isbræ.