# Mapping Radar Glacier Zones and Dry Snow Line in the Antarctic Peninsula Using Sentinel-1 Images
## 4 Results
### Mapping of RGZs  
Based on the image preprocessing procedures and decision tree illuminated in Figure 5, RGZs in the middle of the AP were mapped by using the nine images listed in the right column of Table 1. These images observed the AP in the melting season from 21 October 2014 to 2 March 2015, covering the southern Larsen C Ice Shelf and Graham Land, the George VI Ice Shelf, and the north part of Palmer Land. Compared with the subsequent images, no snowmelt was interpreted on the image taken on 21 October (Figure 8a). This image served as a reference data for the detection of the wet snow radar zone, considering the absence of the earlier image.  
Sentinel-1 images are effective for the interpretations of RGZs in the AP. The RGZs of this region were mapped, and are shown in Figure 8b-i. The middle AP was frozen at the beginning of November. Dry snow and frozen percolation radar zones dominated the mountains and ice shelves, respectively. Bare ice was sporadically distributed in the foothills and the edges of ice shelves (Figure 8a). Snowmelt (red area) expanded quickly in December. Most of the Larsen C and George VI ice shelves were melting at this time (Figure 8b,c). These ice shelves and the coastal areas beside the Bellingshausen Sea were almost totally melting on 1 January of the following year. Melt area retreated from the coastline to the piedmont region of the Graham Land from January to February (Figure 8e-h). The grounding zone of the Larsen C Ice Shelf showed the longest melting season. This phenomenon is consistent with the melting days, as shown in Figure 6b. The middle AP almost refroze on 2 May, except for some small patches distributed along the coastline beside the Bellingshausen Sea (Figure 8i).  
Figure 7: Relationships between melting days, elevation, and backscatter. (**a**) shows the mean melting days at 100 m elevation intervals (blue empty dots). (**b**) shows the mean winter \(\sigma^{0}\) for every five melting days (blue empty dots). The red lines and green bars represent the linear trend and sample size, respectively.  
The wet snow radar zone and frozen percolation radar zone waxed and waned in the freeze-thaw cycle, but the dry snow radar zone remained unchanged the entire time.  
We compared the melt area detected by Sentinel-1 and the SSM/I with the ERA-Interim 2 m air temperature derived from the European Center for Medium-Range Weather Forecasting ([[http://www.ecmw.int/](http://www.ecmw.int/)]([http://www.ecmw.int/](http://www.ecmw.int/))). Melting signals were recognized by remote sensing techniques when the mean air temperature rose above 266 K (Figure 9). Melt area varied greatly with air temperature in the melting season. Wet snow radar zone detected by Sentinel-1 was smaller than the melt area derived from the SSM/I. When Sentinel-1 images were avaliable, the mean melt area identified by Sentinel-1 and the SSM/I was 2.89 \(\times\) 10\({}^{4}\) km\({}^{2}\) and 5.64 \(\times\) 10\({}^{4}\) km\({}^{2}\), respectively.  
Figure 8: RGZs of the middle AP derived from Sentinel-1 images. (**a**) shows the reference image for mapping of the wet snow radar zone. The map on the bottom left shows the location of the images in the AP. (**b–i**) illustrate the dry snow (orange area), frozen percolation (cyan area), wet snow (red area), and bare ice radar zone (blue area) from 2 November 2014 to 2 March 2015.