Four decades of radar-echo sounding: The past, present, and future of radar applications for understanding subglacial environments 

2021 ◽  
Author(s):  
Winnie Chu
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Thermal Conditions ◽  
Machine Learning Algorithms ◽  
Polar Ice Sheets ◽  
Radar Echo ◽  
Radar Applications ◽  
Bed Roughness ◽  
Subglacial Environments ◽  
Echo Sounding

<p>Airborne radar sounding observations have been instrumental in understanding subglacial environments and basal processes of ice sheets. Since the advent of analog radar-echo sounding (RES) system in the early 1970s, there have been tremendous innovations in both RES hardware and signal processing techniques. These technological advancements have provided high-resolution ice thickness measurements, improved detection and characterization of subglacial hydrology, as well as improved understanding of basal thermal conditions, bed roughness and geomorphology, and other processes that govern the basal boundary of the polar ice sheets. In this talk, I will provide an overview of the recent developments in radar processing approaches and system designs and highlight some of the new understanding of ice sheet subglacial processes that emerge from these breakthroughs. I will end by discussing areas where future radar applications and discoveries may be possible, including the utilization of machine learning algorithms, space-borne radar missions, and ground-based passive radar platforms to provide long-term monitoring of ice sheet subglacial environments.</p>

scholarly journals The response of fabric variations to simple shear and migration recrystallization

2015 ◽  
Vol 61 (227) ◽  
pp. 537-550 ◽  
Author(s):  
Joseph H. Kennedy ◽  
Erin C. Pettit
Keyword(s):  
Thermal Activation ◽  
Nearest Neighbor ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Polar Ice ◽  
Climatic Variations ◽  
Fabric Evolution ◽  
Polar Ice Sheets ◽  
Low Levels ◽  
And Migration

AbstractThe observable microstructures in ice are the result of many dynamic and competing processes. These processes are influenced by climate variables in the firn. Layers deposited in different climate regimes may show variations in fabric which can persist deep into the ice sheet; fabric may ‘remember’ these past climate regimes. We model the evolution of fabric variations below the firn–ice transition and show that the addition of shear to compressive-stress regimes preserves the modeled fabric variations longer than compression-only regimes, because shear drives a positive feedback between crystal rotation and deformation. Even without shear, the modeled ice retains memory of the fabric variation for 200 ka in typical polar ice-sheet conditions. Our model shows that temperature affects how long the fabric variation is preserved, but only affects the strain-integrated fabric evolution profile when comparing results straddling the thermal-activation-energy threshold (∼−10°C). Even at high temperatures, migration recrystallization does not eliminate the modeled fabric’s memory under most conditions. High levels of nearest-neighbor interactions will, however, eliminate the modeled fabric’s memory more quickly than low levels of nearest-neighbor interactions. Ultimately, our model predicts that fabrics will retain memory of past climatic variations when subject to a wide variety of conditions found in polar ice sheets.

scholarly journals Ice sheets viewed from the ocean: the contribution of marine science to understanding modern and past ice sheets

2012 ◽  
Vol 370 (1980) ◽  
pp. 5512-5539 ◽  
Author(s):  
Colm Ó Cofaigh
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Major Influence ◽  
Marine Science ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Technological Advances ◽  
Polar Ice Sheets ◽  
History Of ◽  
Geophysical Imaging

Over the last two decades, marine science, aided by technological advances in sediment coring, geophysical imaging and remotely operated submersibles, has played a major role in the investigation of contemporary and former ice sheets. Notable advances have been achieved with respect to reconstructing the extent and flow dynamics of the large polar ice sheets and their mid-latitude counterparts during the Quaternary from marine geophysical and geological records of landforms and sediments on glacier-influenced continental margins. Investigations of the deep-sea ice-rafted debris record have demonstrated that catastrophic collapse of large (10 5 –10 6  km 2 ) ice-sheet drainage basins occurred on millennial and shorter time scales and had a major influence on oceanography. In the last few years, increasing emphasis has been placed on understanding physical processes at the ice–ocean interface, particularly at the grounding line, and on determining how these processes affect ice-sheet stability. This remains a major challenge, however, owing to the logistical constraints imposed by working in ice-infested polar waters and ice-shelf cavities. Furthermore, despite advances in reconstructing the Quaternary history of mid- and high-latitude ice sheets, major unanswered questions remain regarding West Antarctic ice-sheet stability, and the long-term offshore history of the East Antarctic and Greenland ice sheets remains poorly constrained. While these are major research frontiers in glaciology, and ones in which marine science has a pivotal role to play, realizing such future advances will require an integrated collaborative approach between oceanographers, glaciologists, marine geologists and numerical modellers.

scholarly journals The Theory of Thermal Convection in Polar Ice Sheets

1976 ◽  
Vol 16 (74) ◽  
pp. 41-71 ◽  
Author(s):  
T.J. Hughes
Keyword(s):  
Thermal Convection ◽  
Critical Rayleigh Number ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Transient Creep ◽  
Steady State Creep ◽  
Polar Ice ◽  
Ice Streams ◽  
Basal Ice ◽  
Polar Ice Sheets

Abstract Application of thermal convection theory to polar ice sheets (Hughes, 1970, 1971. 1972[a],[c]) is reviewed and expanded. If it occurs, thermal convection is mainly concentrated near the bed of the ice sheet; resulting in active and passive convective flow, respectively below and above the ice density inversion. Convection begins as transient creep when a stress-independent critical Rayleigh number is exceeded, and stabilizes as steady-state creep when a stress-dependent critical Rayleigh number is exceeded. Transient- creep convection begins as unstable ripples in isotherms near the bed, with some ripples becoming upward bulges of basal ice which rapidly shrink laterally and grow vertically to become ascending dikes of recrystallized basal ice during steady-state creep. Sills of basal ice are injected horizontally between weakly coupled layers in the strata of cold ice slowly sinking en masse between dikes. Convection begins under domes of thick ice toward the ice-sheet center and a stable polygonal array of dikes may form if frictional heat creates hot ice at the bed as rapidly as convection flow redistributes hot basal ice in dikes and sills, Advective flow transports the converting ice toward the margin of the ice sheet where dikes converge at the heads of ice streams. Dike—sill convection then becomes ice-stream convection in which the entire ice stream behaves like a dike, uncoupling from the bed, and rising en masse. This would help explain why ice streams flow at surge velocities.

Recent developments in modeling ice sheet deformation

2020 ◽  
Author(s):  
Felicity McCormack ◽  
Roland Warner ◽  
Adam Treverrow ◽  
Helene Seroussi
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Vertical Shear ◽  
Shear Stresses ◽  
Polar Ice ◽  
Ice Flow ◽  
Polar Ice Sheets ◽  
Basal Shear ◽  
The Impact

<p>Viscous deformation is the main process controlling ice flow in ice shelves and in slow-moving regions of polar ice sheets where ice is frozen to the bed. However, the role of deformation in flow in ice streams and fast-flowing regions is typically poorly represented in ice sheet models due to a major limitation in the current standard flow relation used in most large-scale ice sheet models – the Glen flow relation – which does not capture the steady-state flow of anisotropic ice that prevails in polar ice sheets. Here, we highlight recent advances in modeling deformation in the Ice Sheet System Model using the ESTAR (empirical, scalar, tertiary, anisotropic regime) flow relation – a new description of deformation that takes into account the impact of different types of stresses on the deformation rate. We contrast the influence of the ESTAR and Glen flow relations on the role of deformation in the dynamics of Thwaites Glacier, West Antarctica, using diagnostic simulations. We find key differences in: (1) the slow-flowing interior of the catchment where the unenhanced Glen flow relation simulates unphysical basal sliding; (2) over the floating Thwaites Glacier Tongue where the ESTAR flow relation outperforms the Glen flow relation in accounting for tertiary creep and the spatial differences in deformation rates inherent to ice anisotropy; and (3) in the grounded region within 80km of the grounding line where the ESTAR flow relation locally predicts up to three times more vertical shear deformation than the unenhanced Glen flow relation, from a combination of enhanced vertical shear flow and differences in the distribution of basal shear stresses. More broadly on grounded ice, the membrane stresses are found to play a key role in the patterns in basal shear stresses and the balance between basal shear stresses and gravitational forces simulated by each of the ESTAR and Glen flow relations. Our results have implications for the suitability of ice flow relations used to constrain uncertainty in reconstructions and projections of global sea levels, warranting further investigation into using the ESTAR flow relation in transient simulations of glacier and ice sheet dynamics. We conclude by discussing how geophysical data might be used to provide insight into the relationship between ice flow processes as captured by the ESTAR flow relation and ice fabric anisotropy.</p>

scholarly journals Laboratory studies of the flow rates of debris-laden ice

2003 ◽  
Vol 37 ◽  
pp. 108-112 ◽  
Author(s):  
Tim H. Jacka ◽  
Shavawn Donoghue ◽  
Jun Li ◽  
William F. Budd ◽  
Ross M. Anderson
Keyword(s):  
Laboratory Tests ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Laboratory Studies ◽  
Polar Ice ◽  
Flow Rates ◽  
Basal Ice ◽  
Ice Flows ◽  
Polar Ice Sheets ◽  
Deformation Tests

AbstractIce-sheet basal ice is warmer than that above because of the heat from the Earth’s interior. The stresses acting on the basal ice are greatest. In addition, the basal ice often contains debris consisting of silt and small stones picked up from the rock over which the ice flows. Because the base is the warmest part of an ice sheet and the stress there is greatest, flow rates in the basal ice are large and often contribute most of the ice movement. It is therefore important, for accurate modelling of the ice sheets, to know whether the debris within the basal ice enhances or retards the flow of the ice. In this paper, we describe laboratory deformation tests in uniaxial compression and in simple shear, on sand-laden ice. We find no significant dependence of flow rate on sand content (up to 15% volume) in the stress range 0.13–0.5 MPa and temperature range –0.02 to –18.0°C. Further work needs to include laboratory tests on debris-laden ice extracted from the polar ice sheets. This work is underway.

scholarly journals EXTRACTION OF ICE SHEET LAYERS FROM TWO INTERSECTED RADAR ECHOGRAMS NEAR NEEM ICE CORE IN GREENLAND

2016 ◽  
Vol XLI-B7 ◽  
pp. 585-591 ◽  
Author(s):  
S. Xiong ◽  
J.-P. Muller
Keyword(s):  
Ice Core ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Electromagnetic Properties ◽  
Flow Mode ◽  
Internal Layers ◽  
Ice Flow ◽  
The North ◽  
Radar Echo ◽  
Echo Sounder

Accumulation of snow and ice over time result in ice sheet layers. These can be remotely sensed where there is a contrast in electromagnetic properties, which reflect variations of the ice density, acidity and fabric orientation. Internal ice layers are assumed to be isochronous, deep beneath the ice surface, and parallel to the direction of ice flow. The distribution of internal layers is related to ice sheet dynamics, such as the basal melt rate, basal elevation variation and changes in ice flow mode, which are important parameters to model the ice sheet. Radar echo sounder is an effective instrument used to study the sedimentology of the Earth and planets. Ice Penetrating Radar (IPR) is specific kind of radar echo sounder, which extends studies of ice sheets from surface to subsurface to deep internal ice sheets depending on the frequency utilised. In this study, we examine a study site where folded ice occurs in the internal ice sheet south of the North Greenland Eemian ice drilling (NEEM) station, where two intersected radar echograms acquired by the Multi-channel Coherent Radar Depth Sounder (MCoRDS) employed in the NASA’s Operation IceBridge (OIB) mission imaged this folded ice. We propose a slice processing flow based on a Radon Transform to trace and extract these two sets of curved ice sheet layers, which can then be viewed in 3-D, demonstrating the 3-D structure of the ice folds.

scholarly journals Study of Deformations within Ice Sheets due to Bottom Undulations by Means of Radio Echo-Sounding

1979 ◽  
Vol 24 (90) ◽  
pp. 513 ◽  
Author(s):  
S. Overgaard ◽  
K. Rasmussen
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Flow Lines ◽  
Radio Echo Sounding ◽  
Abstract Data ◽  
Surface Profiles ◽  
Technical University ◽  
Glacier Flow ◽  
Echo Sounding

Abstract In order to test the theory of glacier flow over bedrock undulations presented by S. J. Johnsen, K. Rasmussen, and N.Reeh in the accompanying abstract, data from the E.G.I.G. and the Dye-3 flow lines on the Greenland ice sheet have been analysed. The data comprise surface profiles measured by conventional techniques, and ice thicknesses and depths of internal isochronic layers obtained by the Technical University of Denmark by means of radio echo-soundings.

scholarly journals Coherent large beamwidth processing of radio-echo sounding data

2018 ◽  
Vol 12 (9) ◽  
pp. 2969-2979 ◽  
Author(s):  
Anton Heister ◽  
Rolf Scheiber
Keyword(s):  
Ice Sheets ◽  
Internal Layers ◽  
Spectral Filtering ◽  
Polar Ice ◽  
Bed Topography ◽  
Ice Surface ◽  
Radio Echo Sounding ◽  
Polar Ice Sheets ◽  
Slope Estimation ◽  
Echo Sounding

Abstract. Coherent processing of radio-echo sounding data of polar ice sheets is known to provide an indication of bedrock properties and detection of internal layers. We investigate the benefits of coherent processing of a large azimuth beamwidth to retrieve and characterize the orientation and angular backscattering properties of the surface and subsurface features. MCRDS data acquired over two distinct test areas in Greenland are used to demonstrate the specular backscattering properties of the ice surface and of the internal layers, as well as the much wider angular response of the bedrock. The coupling of internal layers' orientation with the bed topography is shown to increase with depth. Spectral filtering can be used to increase the SNR of the internal layers and mitigate the surface multiple. The variance of the bed backscattering can be used to characterize the bed return specularity. The use of the SAR-focused RES data ensures the correct azimuth positioning of the internal layers for the subsequent slope estimation.

Slowdown in Antarctic mass loss from solid Earth and sea-level feedbacks

Science ◽  
2019 ◽  
Vol 364 (6444) ◽  
pp. eaav7908 ◽  
Author(s):  
E. Larour ◽  
H. Seroussi ◽  
S. Adhikari ◽  
E. Ivins ◽  
L. Caron ◽  
...  
Keyword(s):  
Solid Earth ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
West Antarctica ◽  
Spatiotemporal Resolution ◽  
Amundsen Sea ◽  
Polar Ice Sheets ◽  
Short Time ◽  
The Impact

Geodetic investigations of crustal motions in the Amundsen Sea sector of West Antarctica and models of ice-sheet evolution in the past 10,000 years have recently highlighted the stabilizing role of solid-Earth uplift on polar ice sheets. One critical aspect, however, that has not been assessed is the impact of short-wavelength uplift generated by the solid-Earth response to unloading over short time scales close to ice-sheet grounding lines (areas where the ice becomes afloat). Here, we present a new global simulation of Antarctic evolution at high spatiotemporal resolution that captures all solid Earth processes that affect ice sheets and show a projected negative feedback in grounding line migration of 38% for Thwaites Glacier 350 years in the future, or 26.8% reduction in corresponding sea-level contribution.

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