Glacier Mass Balance and Regime: Data of Measurements and ...

2.6.1 Checking data quality1. The first step. This includes the visual identification of gross errors. There are severalexamples of such gross errors (see Table 2.1. and Appendix 2). In all cases an independent source ofinformation was sought to get true data. In other cases the mass balance was recalculated if possible.2. The second step. This involved choosing the more correct source from the number ofpublications for several glaciers. Usually the latest publications were considered as most accurate. Insuch cases several references on sources are given in Appendix 1. For glaciers with no giveninformation as to what source is better, the authors were contacted directly. Remarkable examples ofhow data appeared to be changing in time due to improvements in maps, recalculations of previousresults, etc.) are given in Table 2.3 (Gries and Silvretta Glaciers).3. The third step. This includes recalculation of mass balance and seasonal components. Thedata of area and variables distributed by altitudinal ranges for about 80 glaciers have been recalculated.These data are also presented in Appendix 2 (bold face).We have found that area versus altitude distributions have been calculated precisely enough orwith small errors in many cases. In some cases errors in area have been found to be substantial (seeTable 2.1). The most common problems with the surface area are:(1) Area values have been considered constant from year to year, and then presented as astepwise change at the time of a resurvey. In reality these changes go smoothly, with small change fromyear to year. We made interpolations, where it was possible, between data taken between the times ofgeodetic surveys.(2) Old topographic maps had been used for the entire period of observation (area had not beenadjusted to change in volume). Mass-balance data were recalculated if area had been given as constantover the period of measurements but cumulative mass balance (volume change) showed large negativenumbers (Sarennes, Abramov, and others, see Table 2.3. and Appendix 2).The comparisons made in Table 2.1 (also in 2.3) may serve as examples of errors common whendata are transmitted, recalculated, and prepared for publication. All these steps may cause errors, and thedata presented in Appendixes 1-4 may not be free of this kind of error.Over the whole period of working with the data colleagues have been contacted, sending themdata and receiving in return improved results or additional information. This has been done for glaciersin Alps (M. Kuhn, M. Aellen, O. Reinwarth, M. Funk), Pyrenees (R. Martines Costa), Scandinavia and40