It is now feasible to infer regional mass balance of glaciers on each continent using satellite data from the early 1970s to the present. Measurements of synchronous and non-synchronous changes in glacier mass balance worldwide will allow us to relate those changes to sea level change, and to regional and global climate.

Utilizing regularly-acquired Landsat and SAR image data, one can gain a global perspective on glacier changes over almost a quarter of a century. Glaciers monitored for variations in glacier-terminus position probably account for less than 1 percent of the total number and area of glaciers worldwide, and the number of glaciers monitored for mass balance is only about one-tenth of the total number monitored for terminus variations (Wood, 1988). Thus, in order to study glacier changes worldwide, remote sensing must be employed (UNESCO, in press). Long-term studies of glacier-terminus position change can be accomplished using satellite data (Williams et al., 1997). Sustained change in glacier-terminus position is usually indicative of a mass balance change (Haeberli and Hoelzle, 1995). It is anticipated that, in the future, glacier-facies boundaries can be studied to detect changes that can be related to mass balance using a combination of Landsat and SAR data.

The primary imaging sensors for use in monitoring small glaciers in the world are the visible and near-infrared sensors on the Landsat satellites, since 1972, and the C-band synthetic aperture radar (SAR) sensors on the European Earth Resources Satellite (ERS)-1, -2, on Canada's RADARSAT, and the L-band SAR on the Japanese Earth Resources Satellite-1 (JERS-1). The SAR satellite data have been available continuously since 1991.

Visible and near-infrared Landsat data have been useful for mapping glaciers and ice sheets, and specifically, mapping glacier area, glacier-terminus position, glacier velocity, and snowline position. Dynamic events such as glacier surges and jökulhlaups have also been recorded by Landsat.

Prominent glaciological features that may be detected using SAR data include: detection of melt onset, glacier-terminus position and transient snowline (Fahnestock and others, 1993; Hall and others, 1995). The glacier facies (Benson, 1962) can also be studied. Some of the radar backscatter zones detected by SAR sensors may be, but are not necessarily, related to the glacier facies (Smith and others, in press).

In addition to the use of satellite-derived imagery for glacier mass balance studies, SAR data may be useful for determining streamflow and discharge from glacier-fed streams (Smith and others, 1995; in press)

References

Benson, C.S., 1962, Stratigraphic studies in the snow and firn of the Greenland ice sheet: CRREL Research Report 70.

Fahnestock, M., Bindschadler, R., Kowk, R., and Jezek, K., 1993, Greenland ice sheet surface properties and ice dynamics from ERS-1 SAR imagery: Science, v. 262, no. 5139, p. 1530-1534.

Haeberli, W., and Hoelzle, M., 1995, Application of inventory data for estimating characteristics of and regional climate-change effects on mountain glaciers - a pilot study with the European Alps: Annals of Glaciology, v. 21, p. 206-212.

Hall, D.K., Williams, R.S., Jr., and Sigurðsson , O., 1995, Glaciological observations of Brúarjökull, Iceland, using synthetic aperture radar and thematic mapper satellite data: Annals of Glaciology, v. 21, p. 271-276.

Smith, L.C., Isacks, B.L., Forster, R.R., Bloom, A.L., and Preuss, I., 1995, Estimation of discharge from braided glacial rivers using ERS-1 synthetic aperture radar - first results: Water Resources Research, v. 31, no. 5, p. 1325-1329.

Smith, L.C., Forster, R.R., Isacks, B.L., and Hall, D.K., in press, Seasonal climatic forcings on alpine glaciers revealed using orbital synthetic aperture radar: Journal of Glaciology.

UNESCO, in press, Into the 2nd Century of World Glacier Monitoring - Prospects and Strategies: UNESCO IHP series.

Williams, R.S., Jr., Hall, D.K., Sigurðsson, O., and Chien, J.Y.L., 1997, Comparison of satellite-derived with ground-based fluctuations of the margins of Vatnajokull, Iceland - 1973-1992: Annals of Glaciology, v. 24, p. 72-80.

Wood, F.B., 1988, Global alpine glacier trends, 1960s to 1980s: Arctic and Alpine Research, v. 20, no. 4, p. 404-413.