Sentinel-1 time series for mapping snow cover and timing of snowmelt in Arctic periglacial environments: Case study from the Zackenberg Valley, Greenland
New publication by Sebastian Buchelt, Kirstine Skov, and Tobias Ullmann
Snow cover (SC) and timing of snowmelt are key regulators of a wide range of Arctic ecosystem functions. Both are strongly influenced by the amplified arctic warming and essential variables to understand environmental changes and their dynamics. This study evaluates the potential of Sentinel-1 (S-1) synthetic aperture radar (SAR) time series for monitoring SC and snowmelt with high spatiotemporal resolution to capture their understudied small-scale heterogeneity. We use 97 dual-polarized S-1 SAR images acquired over north-eastern Greenland in the interferometric wide swath mode from the years 2017 and 2018. Comparison of S-1 intensity against SC fraction maps derived from orthorectified terrestrial time lapse imagery indicates an increase of the SAR intensity before a decrease of SC fraction is observed. Hence, increase of backscatter is related to changing snowpack properties during the runoff phase as well as decreasing SC fraction. We here present a novel approach using backscatter intensity thresholds to identify start and end of snowmelt (SOS and EOS), perennial snow and wet/dry SC based on the temporal evolution of the SAR signal. Comparison of SC with orthorectified time lapse imagery indicate that HV polarization outperforms HH when using a global threshold. With a global configuration (Threshold: 4 dB; polarization: HV), the overall accuracy of SC maps was in all cases above 75 % and in more than half cases above 90 % enabling a large-scale SC monitoring at high spatiotemporal resolution (20 m, 6 days) with high accuracy.