Improved Monitoring of Antarctic Ice Shelves Using the Sentinel-1 TOPSAR Acquisition Mode

• Main Author: Glaude, Quentin
• Other Authors: Pattyn, Frank, Barbier, Christian, De Rauw, Dominique
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: ULB - Université Libre de Bruxelles 2022
• Subjects: Antarctica; Ice Shelf; Sentinel-1; SAR; Physical; chemical; mathematical & earth Sciences; Earth sciences & physical geography; Physique; chimie; mathématiques & sciences de la terre; Sciences de la terre & géographie physique; Antarc*; Antarctic; Ice Sheet; Ice Shelves
• Online Access: https://orbi.uliege.be/handle/2268/268249; https://orbi.uliege.be/bitstream/2268/268249/1/Thesis__final.pdf

The Antarctic Ice Sheet is the largest mass of ice on Earth. In contact with the ocean, the ice starts to float and forms an ice shelf. These ice shelves have an important role in the stability of the Antarctic Ice Sheet. They are acting as regulators by restraining the upwards ice flow. The thinning or damage of these ice shelves is directly translated into a decrease of their holding capacity and causes an acceleration of the ice flow and a retreat of the grounding line. In parallel, the European Space Agency developed the Sentinel-1 Synthetic Aperture Radar – SAR satellite, part of the Copernicus program. Sentinel-1 aims at the systematic observation of the Earth in the C-Band radar frequency (5.54 GHz), with a revisit time of 6 to 12 days. This thesis aims to study the ability of Sentinel-1 to improve the monitoring of ice shelves, opening up new opportunities in terms of capturing small-scale events. To begin with, we studied the ice flow velocity on ice shelves using speckle tracking or differential interferometry. SAR interferometry allows measuring local displacements between two acquisition dates. Classical interferometry allows deriving this velocity component only along the line-of-sight direction. This limitation may be overcome using the specificities of the TOPSAR acquisition mode, allowing a bidimensional estimation of the displacements. The ice-motion estimation is far from trivial, and the specific case of ice shelves introduces additional problems in repeat-pass SAR studies. First, the rapid changes due to high displacements induce a rapid temporal decorrelation. We present a technique, coherence tracking, that aims to correct interferograms from these surface movements. Second, impacted by ocean tides and the inverse barometer effect, ice shelves are subject to vertical variations, inducing a bias to be removed. In the thesis, we present an empirical method using double interferograms and a climate model that corrects these false signals. These double interferograms can also be exploited to ...