Differential InSAR for tide modelling in Antarctic ice-shelfgrounding zones

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 time of satellite data acquisition. Here, we combine the sub-centimetre accuracy and spatial benefits of DInSAR with the temporal benefits of tide models to infer the spatiotemporal 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. 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 match DInSAR to 0.84 mm; generally improve traditional tide models by up to −39 % from 10.8 cm to 6.7 cm RMSE against GPS data from areas where ice is in local hydrostatic equilibrium with the ocean; and up to −74 % from 21.4 cm to 5.6 cm RMSE against GPS data in feature-rich coastal areas where contemporary tide-models are most inaccurate. Numerical modelling then reveals a Young’s modulus of E = 1.0 GPa and an ice viscosity of 10 TPa s when finite-element simulations of tidal flexure are matched to 16 days of tiltmeter data; supporting the theory that strain dependent anisotropy may significantly decrease effective viscosity compared to isotropic polycrystalline ice on large spatial scales. Applications of our method range from (i) refining coarsly-gridded tide models to resolve small-scale features at the spatial resolution and vertical accuracy of SAR imagery, to (ii) separating elastic and viscoelastic contributions in the satellite derived flexure measurement and (iii) gaining information about large-scale ice heterogenity in Antarctic ice-shelf grounding zones, the missing key to improve 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.