## 5 Results
### Snow Cover Ratio and Snow Line Altitude through Time  
The minimum SCR per season for HEF, KWF and VNF is shown along with the measured AAR in Figure 6. Both show a high year-to-year variability with SCR values in general somewhat higher than AAR due to the earlier (seldom later) acquisition date. Average AAR values for the first (1985-2000) and second periods (2001-2016) are 62% and 54%, respectively. Whereas the AAR of KWF is always the highest value, for HEF and VNF the ranking is variable. In most cases, the ranking is the same for the SCR values, indicating that glacier specific differences are established early on. Larger deviations are visible for all three glaciers in the years 1994, 2003, 2006, 2012 and 2015, whereas good to very good matches can be found in 1993, 1999, 2000, 2001, 2004, 2009, 2010 and 2016. Very good matches for individual glaciers occur more often for HEF than for the other glaciers. When averaged for all glaciers  
\begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline
**Sensor** & **Date** & **Points (A/V)** & **Percent** & **Sensor** & **Date** & **Points (A/V)** & **Percent** \\ \hline ETM SLC on & 13.09.1999 & 5/6 & 83 & OLI & 10.08.2013 & 6/8 & 75 \\ ETM SLC on & 20.08.2002 & 4/6 & 67 & OLI & 03.09.2016 & 3/3 & 100 \\ ETM SLC off & 12.08.2005 & 3/3 & 100 & TM & 05.08.1988 & 6/6 & 100 \\ ETM SLC off & 26.08.2010 & 7/7 & 100 & TM & 05.07.1994 & 9/9 & 100 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Performance of the snow cover mapping for eight Landsat scenes and four glaciers (5, 8, 17, 20). The columns ’Points (A/V)’ give the number of points (see Figure 3) classified by ASMAG (A) and visually (V) as snow. In total, 43 out of 48 points (90.6%) are classified correctly.  
Figure 5: Visual versus automatic SLA for (**a**) HEF, (**b**) KWF, (**c**) VNF, and (**d**) HJF. For all four glaciers an r\({}^{2}\) > 80% is obtained. The highest variability is found for HJF.  
and for the entire study period, the mean value of the SCR is 58% (STD of 11%) whereas it is 40% for the AAR (18%).  
The time series of the SLA values for all glaciers, as well as the maximum SLA and the ELA measured in the field for HEF, KWF and VNF are shown in Figure 7. A mean SLA of 2979 m is derived for the full sample and study period. From 1985-2000 to 2001-2016 the SLA increased from 2951 m to 3008 m (by 57 m). The maximum SLA in each season is in the majority of the cases lower than the ELA and fluctuates strongest for HEF. HEF often has the lowest SLA, whereas VNF often has the highest SLA. This is in line with the ELA variability but slightly different from the AAR and SCR variations shown in Figure 6. Hence, ELA/AAR (SLA/SCR) values are not exactly mirrored. Four peaks in the ELA can be seen for the years 1991, 1994, 2003 and 2006/07. All these years had exceptionally warm summer periods where ELAs were partly above the highest elevations of the glaciers. Differences to the SLA were very large in these years, in particular for HEF which often suffered from cloud cover on the scenes closest to maximum ablation. In 1991 and 1994 the scenes available for calculating an SLA for HEF had particularly low values due to snowfall events that occurred shortly before image acquisition.