Recent developments of global positioning systems (GPS ) have provided opportunities for rapid and frequent glacier mapping. The speed and accuracy of GPS techniques make them particularly suitable for repeated glacier mapping. Using two receivers in differential mode provides very high accuracy. InJuly 1995, a kinematic differential GPS survey of Austre Okstindbreen, one of the glaciers in the Norwegian national programme of mass-balance studies, provided three-dimensional positions of 2228 points in less than 6.5 h. Handling the data in a geographic information system permitted construction of a triangular irregular network digital terrain model (TIN DTM ), which could be compared with TIN DTMs constructed from 1981 and 1993 surveys based on aerial photogrammetry and electronic distance measurement, respectively. A TIN DTM has advantages over the more usual grid-based DTM, which incorporates many interpolated values, although interpolation also is necessary if contours are to be derived from a TIN model. The aspect and gradient of triangular facets in the 1995 DTM have been used to produce a map which has considerable potential for detailed energy-balance studies of the glacier's accumulation area.

Changes of snow cover thickness measured by conventional mass balance methods and by global positioning system surveying. Geogr. Ann., 81 A (4): 767-776.ABSTRACT. The most labour-intensive and time-consuming part of many mass balance programmes is the acquisition of snow depth data. The standard technique, which involves probing the snow cover at intervals along a series of profiles, generally by an individual on skis, may involve more than 300 discrete measurements along a total of more than 20 km of profiling at a single glacier. Kinematic surveying with a global positioning system (GPS) in differential mode provides much more information about changes of glacier surface level and snow thickness between surveys. The positions of a large number of points can be fixed in a relatively short time by GPS surveying, and the technique is usable in adverse weather conditions. With real-time kinematic GPS surveying, it is possible to return to the same positions (longitude, latitude) during successive field programmes, and a previously followed route can be retraced precisely. GPS surveying facilitates the production of accurate glacier maps for mass balance programmes. Data obtained by snow depth probing and GPS surveying in 1995 at Austre Okstindbreen, the largest glacier of the Okstindan area, Norway (66°N), indicate that repeated GPS surveys are likely to provide a large amount of information on withinyear and between-year changes of surface topography and are not subject to the errors in mass balance calculations which arise from probing snow depths along selected profiles. Kinematic GPS surveying of several glaciers within an area would overcome the difficulties arising when mass balance studies are confined to a single glacier within a particular area.

Recent developments of global positioning systems (GPS) have provided opportunities for rapid and frequent glacier mapping. The speed and accuracy of GPS techniques make them particularly suitable for repeated glacier mapping. Using two receivers in differential mode provides very high accuracy. In July 1995, a kinematic differential GPS survey of Austre Okstindbreen, one of the glaciers in the Norwegian national programme of mass-balance studies, provided three-dimensional positions of 2228 points in less than 6.5 h. Handling the data in a geographic information system permitted construction of a triangular irregular network digital terrain model (TIN DTM), which could be compared with TIN DTMs constructed from 1981 and 1993 surveys based on aerial photogrammetry and electronic distance measurement, respectively. A TIN DTM has advantages over the more usual grid-based DTM, which incorporates many interpolated values, although interpolation also is necessary if contours are to be derived from a TIN model. The aspect and gradient of triangular facets in the 1995 DTM have been used to produce a map which has considerable potential for detailed energy-balance studies of the glacier’s accumulation area.

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