Frezzotti (1993) measured the velocity of Drygalski Ice'longue at 75 points using Landsat 1 MSS (1973) and LandsatTM (1990) images, and found velocities ranging from 626 ± 5 to 719 ± 5 ma −1. The average velocity for the entire ice tongue was 700 ma −1. Lucchitta and others (1993) measured the velocity at 73 points on Drygalski Ice Tingue using Landsat I multispectral scanner (MSS) (1973) and Landsat thematic mapper (TM) (1988) images. These outlet glaciers drain an area of approximately 250-000 km 2 which includes part of Dome C and Talos Dome (Drewry, 1983). The major outlet glaciers of Victoria Land flow into Terra Nova Bay: Reeves and Priestley Glaciers which flow together and form the Nansen Ice Sheet (the name given by the first explorers, although it is really an ice shelf), and David Glacier whose seaward extension is the Drygalski Ice Tongue ( Fig. There have been very few comparisons made between glacier ice velocities inferred from analysis of sequential satellite images and direct measurements from field surveys (Bindschadler and others, 1994, 1996). Reference Thomas, MacAyeal, Eilers, Gaylord, Hayes and BentleyThomas and others, 1984 Reference Stephenson and BindschadlerStephenson and Bindschadler, 1988 Reference Jenkins and DoakeJenkins and Doake, 1991 Reference Hulbe and WhillansHulbe and Whillans, 1994), where velocity was measured by determining the position of markers at two or more times. in situ measurement of velocities has been performed using both Transit and global positioning system (GPS) techniques (e.g. Reference MorganMorgan, 1973 Reference Lucchitta and FergusonLucchitta and Ferguson, 1986 Bind-schadler and Scambos, 1991 Reference Lucchitta, Mullins, Allison and FerrignoLucchitta and others, 1993, Reference Lucchitta, Rosanova and Mullins1995 Reference Bindschadler, Vornberger, Blankenship, Scambos and JacobelBindschadler and others, 1996). Several authors have shown that ice-flow velocities can be determined through measuring the displacement of features observed in pairs of visible or synthetic aperture radar ι SAR ι images (e.g. Moreover, because of logistical problems and difficult environmental conditions, field research in Antarctica has focused on only a lew ice streams and outlet glaciers close to scientific stations or summer camps. The size of the glaciers and the presence of numerous crevasse fields across the ice streams make the glaciers difficult to study by traditional terrestrial field survey. The velocity field of these glaciers is a critical parameter, together with ice thickness, in determining the ice-discharge rate. Although only 13% of the Antarctic coastline consists of these glaciers ( Reference DrewryDrewry, 1983), they discharge about 90% of the snow that falls inl!and of the coastal zone ( Reference Morgan, Jacka, Akerman and ClarkeMorgan and others, 1982). Most of the Antarctic ice sheet is drained by outlet glaciers and ice streams. The mass balance of the Antarctic ice sheet is determined by the difference between the net snow accumulation and ice discharged across the grounding line into the ocean. 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. (lomparison 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. 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. in a study of the dynamics of David Glacier-Drygalski IceTongue and Priestley and Reeves Glaciers, global positioning system (GPS) measurements were made between 19. 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). Average surface velocities were determined by tracking crevasses and other patterns moving with the ice in two sequential satellite images. Measurements derived from remote-sensing research and Held surveys have provided new ice-velocity data for David Glacier-Drygalski Ice Tongue and Priestley and Reeves Glaciers, Antarctica.
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