Calculation of Mass Balance of Glaciers by Remote-Sensing Imagery using Similarity of Accumulation and Ablation Isoline Patterns (Abstract)

Abstract

A number of maps of component isolines of the Maruch Glacier’s (West Caucasus) mass balance compiled on the basis of field observations during 11 years were analyzed.

The total balance of the glacier’s mass seems to be closely associated with the relationship between accumulation and ablation areas by years, while the total values of net accumulation and ablation are fully determined by the surface-area values of accumulation and ablation regions. The layer of residual snow in the nourishment area by the end of the ablation season and the layer of many-year ice melting in the discharge area changes from year to year against the points fixed in space, but their mean specific value according to the above glaciological areas remains constant from year to year.

Using the results and the remote-sensing images, in which the many-year ice and the snow surplus are well distinguished, it is possible to estimate the areas of the ablation and accumulation regions for the studied glacier and then the mass balance, net accumulation, and, naturally, the run-off from the melting many-year ice.

Estimation of the distribution within the glacier of not only “net” but also total values of accumulation and ablation is possible, if this distribution is similar from year to year, and if total values of accumulation and ablation are known at certain points. The multitude of points, for which total accumulation and ablation may be determined by remote-sensing images, is found on the equilibrium line or on the transient snow line of the glacier at any date during the ablation season. In the first instance, ablation and accumulation, the latter being here equal to the former by definition, may be calculated by the mean summer temperature of the air, extrapolated for the corresponding altitude against the nearest meteorological station. Secondly, ablation is calculated by the sum of positive temperatures of the air and by the temperature coefficient of snow melting, extrapolated for the altitude of the transient snow line.

In order to check the hypothesis of the similarity of isoline systems for accumulation and ablation, all the final values for each year and measured at different points have been normalized according to their mean value for each year.

The normalized maps turned out to be similar to each other. Using the regular net of points, we calculated the variation coefficient of normalized values. They were smaller by 0.20 for the whole area of the maps of normalized ablation and for the greater part of the map area of normalized accumulation. A map of mean normalized values was compiled for 11 years. The isoline "unit" on it coincided with the many-year firn line. With the help of this topological map, one can compile maps for distribution of ablation and accumulation on a glacier for any year or moment, for which there are data on the location of the nourishment line or snow line according to a remote-sensing image and for which air temperature at the altitude of these lines may be estimated.

In conclusion, the degree of similarity of the maps of component isolines for the glacier mass balance between different glaciers of the same morphological type was analyzed. For this, we used normalization of not only the characteristics of the glaciers’ mass balances but also of morphological characteristics (altitudinal change, width, etc.). The results point to similarity of distribution of accumulation and ablation among glaciers. This will allow us to extrapolate the principal features of the isoline maps and the described methods of calculation from the studied glaciers to unexplored ones.