IceLines – A new service to monitor Antarctic ice shelf front dynamics

Abstract

<p>Antarctica`s coastline is constantly changing by moving ice shelf margins and glacier tongues. This can influence the discharge of the Antarctic Ice Sheet if ice shelf areas with buttressing forces are involved. By now, glacier and ice shelf front changes are not tracked continuously due to time-consuming manual work. Hence, dynamics of the calving front position are often simplified by using the steady-state-calving assumption for modelling. To provide modelers with frequent and continuous time series of calving front change, we introduce the ice shelf front monitoring service “IceLines”. IceLines monitors major Antarctic ice shelf fronts based on Sentinel-1 radar imagery. The data set is automatically updated on a monthly basis and can be accessed via the EOC GeoService (geoservice.dlr.de) hosted by DLR. IceLines automatically downloads and pre-processes Sentinel-1 data for 36 selected shelves and glaciers, extracts the calving front based on a deep neural network and optimizes the result by post-processing. The processing chain of IceLines presents unprecedented dense time series of calving front change during the era of Sentinel-1 (2014-today). Whereas many previous challenges for automatic calving front detection were tackled (e.g. various glacier morphologies, backscatter changes, different polarizations), some limitations exist for ice shelves with excessive surface melt during summer or dry snow facies close to the front. We will present the current implementation, the derived calving front time series and validation results of IceLines. Discussions with the modelling community are welcome to further improve the IceLines data set for ice sheet and ice shelf modelling applications.</p>

IceLines – A new data set of Antarctic ice shelf front positions

“…The IceLines data set 24 is available at DLR's GeoService and updated on a monthly basis. Front positions are provided as line shapefiles for each ice shelf.…”

“…The shapefiles are in Antarctic polar stereographic projection (EPSG:3031). All IceLines 24 products can be downloaded from the DLR GeoService (https://download.geoservice.dlr.de/icelines/files/) as single GeoPackage or combined ZIP files for each temporal product and ice shelf separated in the folders 'fronts' and 'fronts-eliminated. Moreover, visual exploration of annual and monthly calving front positions is possible via the web browser of the DLR GeoService (https://geoservice.dlr.de/web/maps/eoc:icelines).…”

“…Frontal movement accuracy. To assess how accurately the frontal movement of a calving front can be determined with the IceLines data set 24 , the distance accuracy was calculated along perpendicular centerlines already utilized for the time series generation. The frontal movement accuracy is determined as the mean distance between the manual and automated front along the defined centerlines.…”

“…The front position can deviate from manual delineated fronts due to fast ice, mélange and icebergs close to the front by 209 ± 12 m (5.2 pixel) on dual polarized imagery and 432 ± 21 m (8.8 pixel) for single polarized imagery whereas the frontal movement can be determined with higher accuracies of 63 ± 68 m (1.6 pixel) for dual and 107 ± 126 m (2.7 pixel) for single polarized imagery. Limitations of the IceLines data set 24 exist due to SAR specific backscatter properties. Calving front detections during the occurrence of surface melt or within the dry snow zone (e.g.…”

“…Ronne, Ross and Filchner ice shelves) remain challenging especially with single polarized SAR imagery. But the benefits of illumination-and cloud-independent SAR imagery outweigh these limitations and do not significantly affect the unprecedented value of the IceLines data set 24 represented by regularly updated, circum-Antarctic time series of calving front change.…”