Wintertime evolution of landfast ice stability in Alaska from InSAR

Abstract. Landfast ice in Alaska is experiencing rapid changes in extents and duration, impacting the safety and utility of the ice for Arctic coastal communities. Current datasets of landfast ice only distinguish landfast ice from mobile pack ice, omitting crucial information regarding the relative safety within landfast ice. InSAR (Interferometric Synthetic Aperture Radar) holds promise for identification of landfast ice and measurement of cm-scale deformation from a spaceborne sensor. We use two properties of interferometry: coherence to identify areas of landfast ice, and the interferometric phase gradient to approximate a new metric called apparent strain (εa) which acts as a proxy for estimating the relative stability of the landfast ice. Apparent strain is described as the horizontal gradient of interferometric phase in the line-of-sight displacement. We built on a previous study by Dammann et al. (2019) by assigning quantitative apparent strain values to identify 3 distinct stability classifications of landfast ice: Bottomfast (εa< 1.0x10-5), Stabilized (1.0x10-5 ≤ εa≤ 2.310-5), and Not stabilized (εa > 2.3x10-5). The monthly average apparent strain decreases as the season progresses, achieving the maximum stability in April or May depending on the region. This study introduces a novel approach to identify the relative stability for areas of landfast ice using InSAR. These findings have implications for enhancing the safety and planning of activities on landfast ice for Arctic coastal communities.