Measurement of Changes in the Area and Volume of the
Earth's Large Glaciers with Satellite Sensors
Richard S. Williams, Jr., USGS Abstract
James B. Garvin, NASA, Goddard Space Flight Center
Oddur Sigurðsson, National Energy Authority (Iceland)
Dorothy K. Hall, NASA, Goddard Space Flight Center
Jane G. Ferrigno, USGS
The global observation and measurement of changes in glaciers has been the long-term goal of glaciologists. Although several selected small glaciers have been surveyed and monitored for long periods, more than 100 years in the case of termini fluctuations and more than 50 years in the case of mass-balance measurements, most of the world's glaciers, large and small, have never been studied scientifically. Satellite remote-sensing technology has become an increasingly important tool to glaciologists in the measurement of changes in the areal extent of the Earth's large glaciers (e.g., Antarctic ice sheet, Greenland ice sheet, ice caps, and ice fields) on a global basis (Williams, 1986a; Williams and Ferrigno, 1994). Techniques have also been developed to measure changes in surface topography with radar altimeters (Zwally and others, 1983; Bindschadler and others, 1989) and with laser altimeters (Garvin and Williams, 1993; Krabill and others, 1995a,b; Thomas and others, 1995, Garvin and others, in press) and to determine volumetric change of glaciers. The Antarctic and Greenland ice sheets make up an estimated 99.3 percent of the volume of glacier ice on the planet, and ice caps and ice fields make up most of the remaining volume. Satellite remote-sensing technology represents the only feasible way of measuring and monitoring changes in the area and volume of these large ice masses (Williams, 1985; Williams and others, 1995; Williams and Hall, 1993, in press) .
Calculation of change in area for a large glacier can be accomplished from maps, vertical aerial photographs, and satellite images (Williams, 1986b; Williams, 1987; Hall and others, 1992; Williams and others, 1997). Calculation of change in volume for a large glacier can also be accomplished, if the elevation of the surface can be determined at two time periods. Haakensen (1986) compared sequential maps of two Norwegian glaciers, Hellstugubreen and Gråsubreen, that were compiled by stereophotogrammetric methods, to calculate changes in area and in volume and compare the volumetric changes to ground-based mass-balance measurements. With either airborne (Garvin and Williams, 1993; Garvin and others, in press) or satellite laser altimetry, the surface elevation of a large glacier can be determined from a series of profiles. If the profile grid spacing is sufficient to accurately represent the surface then calculations of elevation changes can be made at the same network of grid points.
The development and deployment of satellite-borne laser altimeters will soon provide
glaciologists with a tool to accurately measure (±1 m) the topographic surface of large ice
masses and, more importantly, permit the calculation of changes in surface elevation and
surface configuration of large glaciers over time. For example, the January 1996 Space
Shuttle Mission (STS-72) carried a Shuttle Laser Altimeter (SLA) instrument into Earth orbit
(SLA-01 experiment) for meter-precision measurements of the Earth's surface topography and
structure between 28.45º north and south latitudes. Vertical accuracy of these data is 1 m,
and 1 m RMS-quality data were achieved across the surface of the Red Sea and Lake Chad.
An August 1997 Space Shuttle Mission (STS-85) carried an SLA instrument into Earth orbit
(SLA-02 experiment) for meter-precision measurements of the Earth's surface between about
57º north and south latitudes. The orbital inclination of STS-85 passed over all of the
Southern Hemisphere except for Antarctica and the Sub-Antarctic islands. Of particular
glaciological interest in South America are its two largest glaciers, the Northern and Southern
Patagonian Ice Fields situated in the southern part of the Andes Mountains on the border
between Chile and Argentina. Future studies, including glaciological investigations, will
utilize extensively laser data that is acquired from space on a repetitive and systematic basis.
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