## 4 Results
### Profile \"Northern Branch\"  
The data along profile \"Northern Branch\", representing the fast moving part of 79 NG (shown in Figure 1), is presented in Figure 5. Firn modelling indicates a transition of a permeable to impermeable surface layer at around 120 km in an upstream located topographic plateau at about 1000 m a.s.l. (see also Figures S2 and S3). The profile crosses supraglacial lakes (grey bars in Figure 5), over which HH and HV backscatter drops, both in summer and winter conditions [5]. In winter the difference of HH and HV backscatter remains nearly constant down to the crevassed area, while in summer the difference increases towards lower elevations, indicating a decreasing volume scattering due to wet surface conditions. Starting from around 140 km surface roughness increases and becomes the dominating effect on radar backscatter and optical reflectance. With the onset of high roughness more of the radar signal is reflected back to the sensor. Moreover, a part of this increase in backscatter can also be explained by side reflections from sharp crevasses that are dominant in this area.  
Most striking is the difference in backscatter between upstream and downstream areas indicating differences in surface characteristics: In the upstream (i.e., higher elevated) region, the backscatter is dominated by the ratio firm pack penetration while further downstream the crevassed surface roughness dominates the signal. Upstream in winter, the backscatter is nearly constant for elevations above 1000 m and decreases quite slowly in lower elevations. In contrast in summer, the backscatter drops very fast around 1500 m a.s.l., indicating a significantly wetter surface below.  
Looking at reflectance values the average for the areas with elevation above 1000 m a.s.l. (distance from the ice margin \(>\) 20 km) showed on April about 0.97, 1.00 and 0.073 for bands 3,  
Figure 4: Profile “Southern Branch” displaying in the upper panel topography and density (**left color bar**) along the flow line (shown in Figure 1), as well as the small (**thin line**) and large scale roughness (**thick line**, coloured with amplitude HH-HV (16 August 2018) of the right color bar). HH and HV backscatter for winter and summer are displayed in the middle panel. Grey bards denote location of supraglacial lakes. The lower panel represents the reflectance of channel B3 (green), Index 1 (red) and Index 2 (grey) of S2 in summer (pale) and winter (dark). The glacier flow direction is from left (upstream) to right (downstream).  
8 and 11, respectively. The values in areas closer to the ice margin (<1000 m a.s.l.) were 0.93, 0.92 and 0.09 for the above mentioned bands and same season. The indexes were also in this case close to each other highlighting the occurrence of similar surface types (Index1: \(-\)0.016 and 0.010: Index2: 0.86 and 0.82). The same analysis evidences on July reflectance values significantly different: 0.89, 0.75 and 0.022 far from the ice margin; 0.71, 0.51 and 0.009 close to the ice margin. The Vis-NIR index (Index 1) highlighted a less significant difference (0.15 versus 0.09) as well as the NIR-SWIR index (Index 2) (0.94 versus 0.95).