## 4 Results
### Snow, Bare and Dark Ice Surface  
The evolution of the snow cover can only be assessed with remote sensing data with a short repetition time, as provided by the MODIS platform. While this platform provides lower spatial resolution, it ensures higher time resolution that can be used to obtain a time series of spectral reflectance during each melting season. This approach was followed by [PERSON] et al. (2013) with the aim of detecting bare ice and dark ice on the surface. We performed such an analysis in the 79 NG area for three consecutive years 2016, 2017 and 2018, focusing particularly on the relationship with the mountains surrounding the floating tongue of the glacier. The reduction of the fractional snow cover occurring on the outcropping rocks showed (Figure 7) that the snow cover started to melt by the end of May - beginning of June in 2016 and 2017 (respectively: 6 June 2016, 30 May 2017) and by the end of June in 2018. The areas closer to the outcropping rocks, ROI1 (120 pixels) and ROI4 (700 pixels) in Figure 1a, showed a change in spectral behavior. In the middle of June in 2016 and 2017 and at the beginning of July in 2018 reflectance values of up to 0.8 at \(\lambda_{860}\) nm (characteristic for snow/firm surface) changed to the ones associated with a bare ice surface (\(<\)0.6 at \(\lambda_{860}\) nm ([PERSON] et al., 2018)).  
Figure 6: Profile “Old Ice” with nearly same panels as Figure 5, except that no laser scanner based roughness is available here. The glacier flow direction is from left (upstream) to right (downstream). The grey bars indicate here Holocene ice (wide bar) and Pleistocene ice (narrow bar), that is detected in S2 imagery following ([PERSON] et al., 2018).  
Both areas, ROI1 and ROI4, reached the lowest values of reflectance (close to 0.4 at \(\lambda_{860}\) nm) in the beginning of August in 2016 and 2017 and in the middle of August in 2018. In contrast, areas ROI2 (678 pixels) and ROI3 (920 pixels), that are situated further upstream and farther away from the mountains, showed consistently high reflectance values throughout the melting period, including a limited period of bare ice emergence in 2016 and 2017. The delayed melting season of 2018 preserved the snow cover further upstream. Looking at the spatial distribution of the different reflectance values, the above mentioned near-infrared band showed higher values in the inner part of the ice sheet with a distance from the outcropping rocks up to 40 km in 2016 and 2017, and 20 km in 2018. In order to identify areas in which dark ice recursively occurred during the various melting seasons, the red band (\(\lambda_{660}\)nm) was examined with regard to its spatial distribution (Figure 8), since it represents the indicator for the detection of dark ice, as defined by [PERSON] et al. (2013).  
Figure 7: Evolution of the snow cover area (SCA) over mountainous areas (black line and left \(y\)-axis) in relation to the reflectance variations at 860 nm in selected areas (coloured markers, right \(y\)-axis) numbered as in Figure 1a. The dashed line represents the reflectance threshold defined by [PERSON] et al. (2013) for discriminating between snow cover and ice. All the considered data were obtained analysing MODIS data as described in Section 3.1.