Preprints
https://doi.org/10.5194/tc-2021-296
https://doi.org/10.5194/tc-2021-296

  12 Oct 2021

12 Oct 2021

Review status: this preprint is currently under review for the journal TC.

Automatic Delineation of Cracks with Sentinel-1 Interferometry for Monitoring Ice Shelf Damages and Calving

Ludivine Libert, Jan Wuite, and Thomas Nagler Ludivine Libert et al.
  • ENVEO IT GmbH, Innsbruck, 6020, Austria

Abstract. Monitoring the evolution of ice shelf damage such as crevasses and rifts is important for a better understanding of the mechanisms controlling the breakup of ice shelves and for improving predictions about iceberg calving and ice shelf disintegration. Nowadays, the previously existing observational gap has been reduced by the Copernicus Sentinel-1 Synthetic Aperture Radar (SAR) mission that provides a continuous coverage of the Antarctic margins with a 6 or 12-day repeat period. These unprecedented coverage and temporal sampling enable for the first time a year-round systematic monitoring of ice shelf fracturing and iceberg calving, as well as the detection of precursor signs of calving events. In this paper, a novel method based on SAR interferometry is presented for an automatic detection and delineation of active cracks on ice shelves. Active cracks cause phase discontinuities in an interferogram that are extracted automatically by applying a Canny edge detection procedure to the spatial phase gradient derived from a SAR interferogram. The potential of the proposed method is demonstrated in the case of Brunt Ice Shelf, Antarctica, using a stack of 6-day repeat Sentinel-1 interferograms acquired between September 2020 and March 2021. The full life cycle of the North Rift is monitored, including the rift detection, its propagation at rates varying between 0.35 km d−1 and 1.29 km d−1, and the final calving event that gave birth to the iceberg A74 on 26 February 2021. The automatically delineated cracks agree well with the eventual location of the ice shelf edge after the iceberg broke off. The stress field variations observed in the interferograms are attributed to a rigid-body rotation of the ice about the expanding tip of the North Rift in response to the rifting activity. The extent of the North Rift is captured by SAR interferometry well before it becomes visible in SAR backscatter images, hence highlighting the high sensitivity of SAR interferometry to small variations in the ice shelf stress field and its potential for detecting early signs of natural calving events, as well as ice shelf fracturing and damage development in response to atmospheric and oceanic warming caused by climate change.

Ludivine Libert et al.

Status: open (until 07 Dec 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Ludivine Libert et al.

Ludivine Libert et al.

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Short summary
Open fractures are important to monitor because they weaken the ice shelf structure. We propose a novel approach using Synthetic Aperture Radar (SAR) Interferometry for automatic delineation of ice shelf cracks. The method is applied to Sentinel-1 images of Brunt Ice Shelf, Antarctica, and the propagation of the North Rift, which led to iceberg calving in February 2021, is traced. It also is shown that SAR interferometry is more sensitive to rifting than SAR backscatter.