Changes of snow cover thickness measured by conventional mass balance methods and by global positioning system surveying

The most labour-intensive and time-consuming parr of many mass balance prog rammes is the acquisition of snow depth data. The standard technique, which involves probing the snow cover at intervals along a series of profiles, g enerally by an individual on skis, may involve more than 300 discrete measu rements 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 poin ts can be fixed in a relatively short time by GPS surveying, and the techni que is usable in adverse weather conditions. With real-time kinematic GPS s urveying, it is possible to return to the same positions (longitude, latitu de) during successive field programmes, and a previously followed route can be retraced precisely. GPS surveying facilitates the production of accurat e glacier maps for mass balance programmes. Data obtained by snow depth pro bing and GPS surveying in 1995 at Austre Okstindbreen, the largest glacier of the Okstindan area, Norway (66 degrees N), indicate that repeated GPS su rveys are likely to provide a large amount of information on within-year an d between-year changes of surface topography and are not subject to the err ors in mass balance calculations which arise from probing snow depths along selected profiles. Kinematic GPS surveying of several glaciers within an a rea would overcome the difficulties arising when mass balance studies are c onfined to a single glacier within a particular area.