Airborne measurement of glacier surface elevation by scanning laser altimeter

Airborne scanning laser altimetry is a relatively new technique for remote sensing of ground elevation. A laser ranger is scanned across a swath beneath the aircraft, producing a two-dimensional distribution of elevations when combined with data on aircraft position and orientation. Smooth snow-covered glaciers are ideal surfaces for laser scanning since they are highly reflective. A new prototype laser system is described together with results from Hardangerjokulen, Norway. An analysis of the data shows that noise levels are very low at around 2 cm, and that repeatability between overlapping swaths is approximately +/- 10 cm. This is consistent with an absolute accuracy of 15 cm or better from manufacturer's and other measurements. Swath widths of over 1 km are attainable, allowing complete coverage of small to medium-sized glaciers using parallel flight tracks. The high accuracy and dense, even coverage (about 20 000 points per km(2)) gives good-quality derived products such as DEMs and enables reliable measurement of glacier volume change. Scanning laser altimetry has many advantages over photogrammetry, which was previously the only remote-sensing method of measuring elevations over large areas but which performs poorly over snow-covered glaciers.