# Mapping Radar Glacier Zones and Dry Snow Line in the Antarctic Peninsula Using Sentinel-1 Images
###### Abstract  
Surface snowmelt causes changes in mass and energy balance, and endangers the stabilities of the ice shelves in the Antarctic Peninsula (AP). The dynamic changes of the snow and ice conditions in the AP were observed by Sentinel-1 images with a spatial resolution of 40 m in this study. Snowmelt detected by the special sensor microwave/imager (SSM/I) is used to study the relationship between summer snowmelt and winter synthetic aperture radar (SAR) backscatter. Radar glacier zones (RGZs) classifications were conducted based on their differences in liquid snow content, snow grain size, and the relative elevations. We developed a practical method based on the simulations of a microwave scattering model to classify RGZs by using Sentinel-1 images in the AP. The summer snowmelt detected by SSM/I and Sentinel-1 data are compared between 2014 and 2015. The SSM/I-derived melting days is used to validate the winter dry snow line (DSL). RGZs derived from Sentinel-1 images suggest that snowmelt expanded from inland of the Larsen C Ice Shelf to the coastal area, whereas an opposite direction was found in the George VI Ice Shelf. The long melting season in the grounding zone of the Larsen C Ice Shelf may result from the adiabatically-dried fohn winds on the east side of the AP. As the uppermost limit of summer snowmelt, DSL was mapped based on the winter Sentinel-1 mosaic of the AP. Compared with the SSM/I-derived melting days, the winter DSL mainly distributed in the areas melted for one to three days in summer. DSL elevations on the Palmer Land increased from south to north. (\(\sigma^{0}\)) at different channels to estimate the snowmelt in Antarctica [6; 7; 8; 9]. When a snowpack starts to melt, the emissivity and absorptivity increase significantly because of the abrupt increase of the dielectric constant, leading to the sudden increase of \(T_{b}\) and decrease of \(\sigma^{0}\)[10; 11]. Methods based on thresholding \(T_{b}\) and \(\sigma^{0}\) time series with a constant or regionally variable were used to detect snowmelt [6; 12; 13; 14; 15]. The edges of freeze-thaw cycles can also be identified by using wavelet transform methods [16; 17]. Compared with radiometer and scatterometer images, SAR images display higher spatial resolution, which enables us to study the detailed pattern of snowmelt, glacial facies, and snow line. In SAR images, backscatter from snow and ice surface is dependent on snow density, liquid water content, grain size, stratigraphy, and surface roughness [18; 19]. Different snow zones on a glacier are identifiable on SAR images [2; 20; 21; 22; 23; 24]. These radar glacier zones (RGZs), including wet snow, frozen percolation, dry snow, superimposed ice, and bare ice radar zone, can be classified by \(\sigma^{0}\) and elevations [8; 18]. The distribution of RGZs depend on terrain and climate conditions. In the Antarctic, where air temperature is much lower than the temperature of mountain glaciers, snowmelt occurs on the flat ice shelves, and meltwater flow is limited due to the relatively high latitude. As a result, the superimposed ice radar zone is absent [16]. On the other hand, there is no dry snow zone for the places with all the snow and ice surface melting in summer. The transient firm line is the boundary between the bare ice radar zone and wet snow radar zone (summer) or frozen percolation radar zone (winter), which documents the current uppermost limit of the ablation area. At the end of the ablation season, the transient firm line is often regarded as the equilibrium line, which is a key parameter for the glaciers' mass balance [19]. In winter, the boundary of frozen percolation radar zone and dry snow radar zone represents the uppermost limit of the last summer snowmelt, and the position is regarded as the dry snow line (DSL) [8].