Abstract
Abstract. Differential interferometric synthetic aperture radar (DInSAR) is an essential tool for detecting ice-sheet motion near Antarctica's oceanic margin. These space-borne measurements have been used extensively in the past to map the location and retreat of ice-shelf grounding lines as an indicator for the onset of marine ice-sheet instability and to calculate the mass balance of ice sheets and individual catchments. The main difficulty in interpreting DInSAR is that images originate from a combination of several SAR images and do not indicate instantaneous ice deflection at the times of satellite data acquisitions. Here, we combine the sub-centimetre accuracy and spatial benefits of DInSAR with the temporal benefits of tide models to infer the spatio-temporal dynamics of ice–ocean interaction during the times of satellite overpasses. We demonstrate the potential of this synergy with TerraSAR-X data from the almost-stagnant southern McMurdo Ice Shelf (SMIS). We then validate our algorithm with GPS data from the fast-flowing Darwin Glacier, draining the Antarctic Plateau through the Transantarctic Mountains into the Ross Sea. We are able to reconstruct DInSAR-derived vertical displacements to 7 mm mean absolute residual error and generally improve traditional tide-model output by up to 39 % from 10.8 to 6.7 cm RMSE against GPS data from areas where ice is in local hydrostatic equilibrium with the ocean and by up to 74 % from 21.4 to 5.6 cm RMSE against GPS data in feature-rich coastal areas where tide models have not been applicable before. Numerical modelling then reveals Young's modulus of E=1.0±0.56 GPa and an ice viscosity of ν=10±3.65 TPa s when finite-element simulations of tidal flexure are matched to 16 d of tiltmeter data, supporting the hypothesis that strain-dependent anisotropy may significantly decrease effective viscosity compared to isotropic polycrystalline ice on large spatial scales. Applications of our method include the following: refining coarsely gridded tide models to resolve small-scale features at the spatial resolution and vertical accuracy of SAR imagery, separating elastic and viscoelastic contributions in the satellite-derived flexure measurement, and gaining information about large-scale ice heterogeneity in Antarctic ice-shelf grounding zones, the missing key to improving current ice-sheet flow models. The reconstruction of the individual components forming DInSAR images has the potential to become a standard remote-sensing method in polar tide modelling. Unlocking the algorithm's full potential to answer multi-disciplinary research questions is desired and demands collaboration within the scientific community.
Highlights
The periodic rise and fall of the ocean’s surface is caused by the gravitational interplay of the Earth–Moon–Sun system and our planet’s rotation
In contrast to the simple geometry at the southern McMurdo Ice Shelf (SMIS), the Darwin Glacier consists of a feature-rich embayment that is constrained by steep topography at its margins
We presented a data fusion method between differential interferometric synthetic aperture radar (DInSAR) and traditional Antarctic tide models to predict spatial variability in tidal motion near the grounding line
Summary
The periodic rise and fall of the ocean’s surface is caused by the gravitational interplay of the Earth–Moon–Sun system and our planet’s rotation. While DInSAR has often been applied to detect the grounding-line movement around Antarctica (Konrad et al, 2018) the signal can be used to measure spatial variability in ocean tides at very high ground resolution (Minchew et al, 2017; Baek and Shum, 2011). This second application is complicated by the fact that DInSAR interferograms show a combination of multiple stages of the tidal oscillation. Tidal migration of the grounding line as well as viscoelastic time delays in ice displacement, tidally induced velocity variations and geometric effects on the surface flexure complicate the correct interpretation of DInSAR interferograms to date (Rack et al, 2017; Wild et al, 2018)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
