| Summary: | Measurements derived from remote-sensing research and field surveys have provided new ice-velocity data for David Glacier-Drygalski Ice Tongue and Priestly and Reeves Glaciers, Antarctica. Average surface velocities were determined by tracking crevasses and other patterns moving with the ice in two sequential satellite images. Velocity measurements were made for different time intervals (1973-90, 1990-92, etc.) using images from various satellite sensors (Landsat 1 MSS, Landsat TM, SPOT XS). In a study of the dynamics of David Glacier-Drygalski Ice Tongue and Priestley and Reeves Glaciers, global positioning system (GPS) measurements were made between 1989 and 1994. A number of points were measured on each glacier: five points on David Glacier, three on Drygalski Ice Tongue, two on Reeves Glacier-Nansen Ice Sheet and two on Priestley Glacier. Comparison of the results from GPS data and feature-tracking in areas close to image tie-points shows that errors in measured average velocity from the feature-tracking may be as little as ±15-20 m a-1. In areas far from tie-points, such as the outer part of Drygalski Ice Tongue, comparison of the two types of measurements shows differences of about ±70 m a-1.
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