Ice Shelf Area and Ice Shelf Area Change from Sentinel-1 SAR

Abstract

Floating ice shelves fringe 74% of Antarctica's coastline, directly linking the ice sheet and the surrounding oceans. The landward extent of the ice shelf is the grounding line, which marks the transition of grounded ice to the ice shelf, and its seaward limit is the ice shelf front, which is the boundary between the shelf and the ocean. The change in ice shelf area is an important indicator of ice shelf stability in a warming climate, being affected by grounding line retreat as a possible consequence of ice thinning and calving events at the front, culminating with ice shelf disintegration or collapse. Two independent processing chains developed at DLR's Earth Observation Center are used to quantify the ice shelf perimeter around Antarctica. For the ice shelf fronts, we use IceLines, a deep learning-based framework providing calving front locations (CFL) on different temporal scales (daily, monthly, quarterly, annual) for Antarctic ice shelves automatically extracted from Sentinel-1 radar imagery. The procedure is operational, and monthly releases of the datasets are available on the DLR's GeoService data portal (https://download.geoservice.dlr.de/icelines/files/). The time series of gapless grounding lines is more challenging to obtain due to limited timely and coherent SAR acquisitions. We use the time-annotated Grounding Line Location (GLL) product of ESA's Antarctic Ice Sheet Climate Change Initiative to derive an average grounding line for a certain period, e.g., one year. Our custom procedure fills the gaps with grounding lines from manual and machine-learning delineations of temporally close Sentinel-1 DInSAR interferograms and external datasets. This study presents ice shelf area changes derived with a novel method that was developed to combine the grounding lines derived from Sentinel-1 A/B with contemporaneous Sentinel-1 A/B-based ice shelf fronts. By analyzing area change based on changes in the ice shelf front and the grounding line we can attribute area change to either grounding line retreat or ice shelf calving, providing information about the causes of an area change. Examples of annual ice shelf perimeters of major ice shelves from the start of the Sentinel-1 era to the present will be presented and discussed.