Abstract
AbstractThe mass balance of Glacier de Sarennes, French Alps, has been measured since 1949, using the glaciological method based on core and ablation stake data, and area extrapolations, to find the overall glacier balance. The cumulative balance obtained in this way is very dependent on systematic errors that can increase linearly with the number, N, of measurement years, whereas random errors rise with . The volumetric-balance method based on aerial photogrammetry provides results whose errors do not depend on the number of years. This method was used to test field measurements for the period 1952–2003 and gives a mass balance of −32.30 ± 1.04 m w.e. compared to −34.89 ± 1.15 m w.e. based on field data. The discrepancy between the two methods is discussed on the basis of a careful error analysis. Moreover, the possibility of using the volumetric method to detect biases in field measurements is evaluated in terms of two types of errors. The number and locations of measurement sites required to account for all the spatial and temporal variabilities of the mass balance is discussed by variance analysis. Methodological implications and recommendations are presented to provide mass-balance measurements of the best possible accuracy.
Highlights
ObjectivesMountain-glacier mass balances are excellent indicators of climate change over the last few centuries (Oerlemans and Fortuin, 1992; Haeberli, 1995)
The mass balance of Glacier de Sarennes, French Alps, has been measured since 1949, using the glaciological method based on core and ablation stake data, and area extrapolations, to find the overall glacier balance
The traditional field-measurement method is the glaciological method, in which yearly point mass balances are obtained from stakes inserted in ice and from cores drilled in firn
Summary
ObjectivesMountain-glacier mass balances are excellent indicators of climate change over the last few centuries (Oerlemans and Fortuin, 1992; Haeberli, 1995). When extrapolated to the whole surface of the glacier and added year after year, the resulting cumulative glacierwide balance is likely to be very sensitive to systematic errors which accumulate linearly with the number of measurement years (denoted as N; see List of symbols). Such systematic errors will determine the exactness (veracity) of the method. Its precision (reproducibility) will depend on random erproffiffirffiffis that increase in the cumulative mass balance only with N Discerning these two types of errors requires an independent method for which the intrinsic error is as small as possible and not time-dependent
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