Abstract
Ice shelves—the floating extensions of the Antarctic ice sheet—regulate the Antarctic contribution to sea-level rise by restraining the grounded ice flowing from upstream. Therefore, ice-shelf change (e.g., ice-shelf thinning) results in accelerated ice discharge into the ocean, which has a direct effect on sea level. Studying ice-shelf velocity allows the monitoring of the ice shelves’ stability and evolution. Differential synthetic aperture radar interferometry (DInSAR) is a common technique from which highly accurate velocity maps can be inferred at high resolution. Because ice shelves are afloat, small sea-level changes—i.e., ocean tides and varying atmospheric pressure (aka inverse barometer effect) lead to vertical displacements. If not accounted for in the interferometric process, these effects will induce a strong bias in the horizontal velocity estimation. In this article, we present an empirical DInSAR correction technique from geophysical models and double DInSAR, with a study on its variance propagation. The method is developed to be used at large coverage on short timescales, essential for the near-continuous monitoring of rapidly changing areas on polar ice sheets. We used Sentinel-1 SAR acquisitions in interferometric wide and extra -wide swath modes. The vertical interferometric bias is estimated using a regional climate model (MAR) and a tide model (CATS2008). The study area is located on the Roi Baudouin Ice Shelf in Dronning Maud Land, East Antarctica. Results show a major decrease (67 m $\cdot$ a $^{-1}$ ) in the vertical-induced displacement bias.
Highlights
T HINNING of Antarctic ice shelves and the corresponding decrease in the restraint experienced by inland ice flow [3], [4] are recognized as major drivers of current Antarctic ice loss [5]
We describe a fast implementable empirical technique that is capable of removing the main contribution of vertical displacements using double difference synthetic aperture radar (SAR) interferograms and geophysical models
Ice shelves are subject to vertical fluctuations related to tides and varying atmospheric pressure, which introduce a bias in the computation of the horizontal displacements by differential SAR interferometry
Summary
T HINNING of Antarctic ice shelves (the floating extensions of ice sheets [1], [2]) and the corresponding decrease in the restraint experienced by inland ice flow [3], [4] are recognized as major drivers of current Antarctic ice loss [5]. Ice-shelf thinning causes an instantaneous acceleration and a retreat of the grounding line, i.e., the limit between the grounded ice sheet and the floating ice shelf [7] These consequences lead to an increase in ice discharge into the ocean, a contribution to sea level rise. Interferometry, in particular, is an essential tool to monitor ice-shelf behavior by deriving ice flow fields and tracking grounding line positions over time, among others. This has led to the continental-wide mapping of the surface velocities in Antarctica [8], which is the basis for all major ice-sheet model predictions [9]. Ice velocity is essential for determining the current state of the ice sheet to determine its basinwise mass balance through the input–output method, in combination with atmospheric modeling [5]
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