Consideration of the errors inherent in mapping historical glacier positions in Austria from the ground and space (1893-2001)

The historical record of in situ measurements of the terminus positions of the Pasterze and Kleines Fleisskees glaciers in the eastern Alps of Austria is used to assess uncertainties in the measurement of decadal scale changes using satellite data. Topographic maps beginning in 1893, and satellite data from 1976 to 2001, were studied in concert with ground measurements to measure glacier changes. Ground measurements show that the tongue of the Pasterze Glacier receded similar to 1150 m from 1893 to 2001, while satellite-derived measurements, using August 2001 Landsat Enhanced Thematic Mapper Plus (ETM+) data registered to an 1893 topographic map, show a recession of 1300-1800 m, with an unknown error. The measurement accuracy depends on the registration technique and the pixel resolution of the sensor when two satellite images are used. When using topographic maps, an additional source of error is the accuracy of the glacier position shown on the map. Between 1976 and 2001, Landsat-derived measurements show a recession of the terminus of the Pasterze Glacier of 479 136 m (at an average rate of 19.1 m a(-1)) while measurements from the ground showed a recession of 428 m (at an average rate of 17.1 m a(-1)). Four-meter resolution Ikonos satellite images from 2000 and 2001 reveal a shrinkage of 22,096 +/- 46 m(2) in the Pasterze tongue. The nearby Kleines Fleisskees glacier lost 30% of its area between 1984 and 2001, and the area of exposed ice increased by 0.44 +/- 0.0023 km(2), according to Landsat satellite measurements. As more recent satellite images are utilized, especially data that are geocoded, the uncertainty associated with measuring glacier changes has decreased. It is not possible to assess the uncertainty when an old topographic map and a satellite image are coregistered. (C) 2003 Elsevier Inc. All rights reserved.