Although mountain glaciers and small ice caps comprise only about three percent of the glacierized area of the earth, they are particularly important in connection with changes in climate and sea level. In the case of an increase of 1 K in mean temperature over a long time period is theoretically sufficient to cause a decrease in length of up to 20 percent for glaciers in North America. In the case of sea level a significant part of the ongoing 1 to 2 mm per year rise in sea level is believed to be due to the thinning of mountain glaciers and small ice caps. this is because of their high rates of mass exchange, with large accumulation in winter and large melting rates in summer.

Because it is difficult to measure glacier mass balance by conventional ground-based methods, balance is monitored on only a handful of glaciers in North America. We have therefore developed an airborne elevation profiling system suitable for rapid measurement of elevation (and, thus, volume changes of these glaciers.

The key components of the system are a laser altimeter for measuring the distance from a small aircraft to the glacier surface, a gyro and compass for determining the pointing direction of the laser beam, and continuous kinematic Global Positioning System (GPS) equipment for determining the exact position of the aircraft during the flight over a glacier. The data is collected by an onboard computer and later processed to give an elevation profile along a specific track on the surface of the glacier. The resulting elevation profile is accurate to 0.3 m or better.

Several glaciers in Alaska have been profiled with this system, and many others will be. These recent profiles are being compared to topographic maps, most of which were made in the 1950s. Such comparisons will then be used to determine how the glaciers in North America have changed in the last few decades, and to infer what changes in the climate are leading to these changes in glacier volume. With the addition of real-time differential GPS navigation, we are also able to make repeat profiles on selected glaciers at one to two year intervals, and therefore measure volume changes on the time scale of a few years.

NASA Grant NAGW-3727 and NOAA Grant ??: Scientific personnel; W. Harrison, K. Echelmeyer, C. Larsen, J. Sapiano, J. Mitchell.