Determination of Changes in the Volume of Mountain Glaciers
Using Airborne Laser Altimetry


Keith Echelmeyer, William D. Harrison, Joseph J. Sapiano, Guðfinna Aðalgeirsdóttir,
Laurence Sombardier, Bernard T. Rabus, and Jeannette (DeMallie) Gorda
University of Alaska-Geophysical Institute

The changing volume of mountain glaciers in Alaska, Canada and the northwestern United States is believed to provide a significant contribution to the ongoing rise in sea level, and it is also a quality indicator of climatic change. In order to measure these changes, we have developed a compact, lightweight and relatively inexpensive laser profiling system which can be mounted in small aircraft capable of operating in mountain valleys. The system consists of a laser ranger for measuring the height of the aircraft above the glacier surface, a vertical axis gyroscope for determining the pointing direction of the laser, and Global Positioning System (GPS) receivers operated in kinematic mode for determining the position of the aircraft. Surface elevation profiles resulting from this system are accurate to about 0.3 m over a wide variety of surfaces and surface slopes (Echelmeyer and others, 1996).

Volume changes over decadal time scales can be obtained by comparison of these surface profiles with existing maps, while recent changes over shorter time scales can be obtained by repeat laser profiling. The accuracy of the longer-time scale volume changes is limited by the accuracy of the existing maps, which is on the order of 5 to 10 m.

Over the past 5 years we have profiled over 60 glaciers in Alaska, Canada and Washington. The broad spectrum of glaciers which we have profiled cover most of the climatic zones where glaciers occur in western North America, and cover many different sizes and types of mountain glaciers. They include small glaciers in the Brooks Range of arctic Alaska, which are very sensitive to the amplified climatic changes predicted in the Arctic; small glaciers in western Alaska, which are indicators of climatic change in the Bering Sea region; large glaciers along the Gulf of Alaska, which are thought to be major contributors to sea level rise; surging glaciers before and during surge; both terrestrial and tidewater glaciers along the coast of Alaska and British Columbia; and the smaller glaciers in the Cascades and Olympic Mountains of Washington.

Preliminary results show that regional trends in mass balance are complex, but most glaciers studied have undergone a loss of mass since the 1950's. It is interesting to note that not all termini have retreated over the same period.

Echelmeyer, K.A., Harrison, W.D., Larsen, C.F., Sapiano, J., Mitchell, J.E., DeMallie, J., Rabus, B., Aðalgeirsdóttir, G., and Sombardier, L., 1996, Airborne surface profiling of glaciers: a case-study in Alaska: Journal of Glaciology, v. 42, no. 142, p. 538-547.

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