#	Pagina
attuale pagina	/open-h2020/projects/208364/results.html

Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - BRISRES (The Basal Roughness of Ice Sheets from Radio-Echo Sounding)

Teaser

Summary

Radar-sounding enables constraints to be placed upon basal topography of ice-sheets, the physical properties of the basal interface, and the internal ice-sheet structure. In turn, this radar-derived information enables more accurate model predictions of ice-sheet evolution and the contribution of ice-sheets to global sea-level rise in a warming world. On a more basic science level, radar-sounding enables exploration and physical characterization of inaccessible regions of the earth surface, with the `discoveryâ€™ aspect of the technique of wide-interest to society.

Firstly, this fellowship has focused upon using radar-sounding data to constrain basal properties of the Greenland Ice Sheet (primarily bed roughness, but also basal water and temperature). As a primary objective, this involved producing a new map of `fine-scaleâ€™ roughness (hypothesized to relate to friction as a glacier slides over its bed) and comparing this with ice motion. Additionally, the fellowship aimed to explore relationships between bed roughness and underlying geology and lithology (in particular - presence or absence of deformable sediment).

Secondly, this fellowship has focused upon the measurement of ice fabric (the orientation distribution of ice crystals) from polarimetric radar sounding. Ice fabric is an important, but poorly parametrized, component of ice rheology (the physics governing ice deformation/flow). The fellowship objectives included the development of a new measurement technique, and the application of the technique to fast-flowing ice streams (the main drainage pathways of ice-sheets).

Work performed

The work performed in the fellowship is subdivided into two areas: (i) basal properties/roughness of Greenland, (ii) measurement of fine-scale englacial structure using phase-sensitive polarimetric radar- sounding. Work performed in the first area includes extraction of Greenland bed-echo data/waveforms, data combination scheme for different radar systems, and exploration of the relationship between roughness, ice velocity and subglacial geology for Greenland. Work performed in the second area includes the development of polarimetric coherence data analysis technique for radar-sounding, the adaptation of polarimetric radar backscatter model to interpret data, validation using ice core fabric data.

Jordan et al. 2018 and Cooper et al. 2019 (see technical report) both produced new constraints for the basal properties of the Greenland Ice Sheet (water/thermal regime and bed roughness respectively). A notable finding in Jordan et al. 2018 was the basal water distribution in the interior of the ice sheet supports recent predictions for the path of Iceland hotspot. A notable finding in Cooper at al. 2019 was that many of the contiguous smoother regions in the interior likely correspond to hard bedrock (rather than the previous interpretation of large pools of water). Jordan et al. 2019 developed a new technique to measure ice crystal orientation fabric from radar sounding. The paper performed a detailed comparison/validation with ice core data from the NEEM ice divide, Greenland

Final results

State of the art: Jordan et al. 2018 and Cooper et al. 2019 both developed radar data analysis methods that addressed new approaches to combine radar systems and compiled with more radar data-sets than previous studies. Jordan et al. 2018 performed a new comparison between radar-derived basal water, other predictions for the basal thermal regime, geothermal heat flux. Cooper et al. 2019 contained the first assessment of bed roughness-anisotropy across the Greenland Ice Sheet and the first assessment of scattering-derived roughness at the ice-sheet scale. Jordan et al. 2019, demonstrated that the new (phase-based) technique to measure fabric improved significantly upon past (power-based) methods.
Ongoing fellowship work is focused on using the new technique in Jordan et al. 2019 to measure the fabric of fast-flowing ice: Whillans Ice Stream and Rutford Ice Stream, both in West Antarctica. The expected results will enable a new data-driven characterization of anisotropic rheology (direction-dependence of ice flow) in ice streams.