scholarly journals Surface Velocity Determination on Large Polar Glaciers by Aerial Photogrammetry

1986 ◽  
Vol 8 ◽  
pp. 22-26 ◽  
Author(s):  
H. H. Brecher
Keyword(s):  
Strain Rate ◽  
Flow Regime ◽  
Surface Velocity ◽  
Control Points ◽  
West Antarctica ◽  
Ice Flow ◽  
Elapsed Time ◽  
Aerial Photogrammetry ◽  
Ice Surface ◽  
Ice Stream B

Aerial photogrammetric block triangulation, a standard and well-developed technique for extending accurate control for mapping into the interior of a region from a few points of known position on its perimeter, can be readily adapted to determine surface velocities on bodies of ice which are too large, and often too crevassed, to be studied effectively by conventional ground surveying. Velocities are calculated from the changes in positions of the same natural surface features determined from photography of two (or more) epochs and the elapsed time. This method is capable of providing many uniformly-spaced measurements over the whole, moving, ice surface, thus allowing the production of maps of velocity and strain-rate, which are valuable in analyzing the ice-flow regime. Results from measurements completed some years ago on Byrd Glacier, one of the largest outlet glaciers from the East Antarctic plateau, are presented as an example of what the method can yield. By means of Doppler satellite surveying, relative positions of control points for each photography epoch can be determined with sub-meter accuracy, making the technique suitable also in regions where no fixed land features exist. A brief description of a project under way in such an area, on Ice Stream B in West Antarctica, is given.

scholarly journals Surface Velocity Determination on Large Polar Glaciers by Aerial Photogrammetry

1986 ◽  
Vol 8 ◽  
pp. 22-26 ◽  
Author(s):  
H. H. Brecher
Keyword(s):  
Strain Rate ◽  
Flow Regime ◽  
Surface Velocity ◽  
Control Points ◽  
West Antarctica ◽  
Ice Flow ◽  
Elapsed Time ◽  
Aerial Photogrammetry ◽  
Ice Surface ◽  
Ice Stream B

Aerial photogrammetric block triangulation, a standard and well-developed technique for extending accurate control for mapping into the interior of a region from a few points of known position on its perimeter, can be readily adapted to determine surface velocities on bodies of ice which are too large, and often too crevassed, to be studied effectively by conventional ground surveying. Velocities are calculated from the changes in positions of the same natural surface features determined from photography of two (or more) epochs and the elapsed time. This method is capable of providing many uniformly-spaced measurements over the whole, moving, ice surface, thus allowing the production of maps of velocity and strain-rate, which are valuable in analyzing the ice-flow regime. Results from measurements completed some years ago on Byrd Glacier, one of the largest outlet glaciers from the East Antarctic plateau, are presented as an example of what the method can yield. By means of Doppler satellite surveying, relative positions of control points for each photography epoch can be determined with sub-meter accuracy, making the technique suitable also in regions where no fixed land features exist. A brief description of a project under way in such an area, on Ice Stream B in West Antarctica, is given.

scholarly journals Delineation of a catchment boundary using velocity and elevation measurements

1998 ◽  
Vol 27 ◽  
pp. 140-144 ◽  
Author(s):  
S. F. Price ◽  
I. M. Whillans
Keyword(s):  
Field Measurements ◽  
Surface Velocity ◽  
Data Sampling ◽  
West Antarctica ◽  
Ice Surface ◽  
Ice Stream ◽  
Elevation Data ◽  
Boundary Location ◽  
Ice Stream B

The determination of catchment boundaries is a major source of uncertainty in net balance studies on large ice sheets. Here, a method for defining a catchment boundary is developed using new measurements of ice-surface velocity and elevation near the Ice Stream B/C boundary in West Antarctica. An objective method for estimating confidence in the catchment boundary is proposed. Using elevation data, the resulting mean standard deviation in boundary location is 13 km in position or 6000 km2 in area. Applying a similar uncertainty to both sides of the Ice Stream Β catchment results in a catchment-area uncertainty of 9%. Much larger uncertainties arise when the method is applied to velocity data. The uncertainty in both cases is primarily determined by the density of field measurements and is proportionally similar for larger catchment basins. Differences in the position of the velocity-determined boundary and the elevation-determined boundary probably result from data sampling. The boundary positions determined here do not support the hypothesis that Ice Stream Β captured parts of the Ice Stream C catchment.

scholarly journals Are longitudinal ice-surface structures on the Antarctic Ice Sheet indicators of long-term ice-flow configuration?

2014 ◽  
Vol 2 (2) ◽  
pp. 911-933 ◽  
Author(s):  
N. F. Glasser ◽  
S. J. A. Jennings ◽  
M. J. Hambrey ◽  
B. Hubbard
Keyword(s):  
Flow Line ◽  
Ice Sheet ◽  
Surface Structures ◽  
Surface Velocity ◽  
Ice Flow ◽  
Antarctic Ice Sheet ◽  
Ice Surface ◽  
Ice Stream ◽  
The Antarctic

Abstract. Continent-wide mapping of longitudinal ice-surface structures on the Antarctic Ice Sheet reveals that they originate in the interior of the ice sheet and are arranged in arborescent networks fed by multiple tributaries. Longitudinal ice-surface structures can be traced continuously down-ice for distances of up to 1200 km. They are co-located with fast-flowing glaciers and ice streams that are dominated by basal sliding rates above tens of m yr-1 and are strongly guided by subglacial topography. Longitudinal ice-surface structures dominate regions of converging flow, where ice flow is subject to non-coaxial strain and simple shear. Associating these structures with the AIS' surface velocity field reveals (i) ice residence times of ~ 2500 to 18 500 years, and (ii) undeformed flow-line sets for all major flow units analysed except the Kamb Ice Stream and the Institute and Möller Ice Stream areas. Although it is unclear how long it takes for these features to form and decay, we infer that the major ice-flow and ice-velocity configuration of the ice sheet may have remained largely unchanged for several thousand years, and possibly even since the end of the last glacial cycle. This conclusion has implications for our understanding of the long-term landscape evolution of Antarctica, including large-scale patterns of glacial erosion and deposition.

scholarly journals Seismic-Reflection Profiling of a Widespread Till Beneath Ice Stream B, West Antarctica (Abstract)

1988 ◽  
Vol 11 ◽  
pp. 210 ◽  
Author(s):  
Sean T. Rooney ◽  
D. D. Blankenship ◽  
R. B. Alley ◽  
C. R. Bentley
Keyword(s):  
Seismic Reflection ◽  
Ross Sea ◽  
High Porosity ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Flow ◽  
West Antarctic ◽  
Ice Stream ◽  
Seismic Reflection Profiling ◽  
Ice Stream B

Seismic-reflection profiling has previously shown that, at least at one location. Ice Stream Β in West Antarctica rests on a layer of till a few meters thick (Blankenship and others 1986). Analyses of both compressional- and shear-wave seismic reflections from the ice–till boundary confirm the results of those earlier studies, which showed that the till is water-saturated and has a high porosity and low differential pressure. We conclude that this till is basically homogeneous, at least on a scale of tens of kilometers, though some evidence that its properties vary laterally can be discerned in these data. We propose that the till is widespread beneath Ice Stream Β and probably also beneath the other West Antarctic ice streams. Our seismic profiling shows that the till is essentially continuous beneath Ice Stream Β over at least 12 km parallel to ice flow and 8 km transverse to flow. Beneath these profiles the till averages about 6.5 m thick and is present everywhere except possibly on isolated bedrock ridges parallel to ice flow. The till thickness on these bedrock ridges falls to less than 2 m, the limit of our seismic resolution, but there is evidence that the ridges do not impede ice flow substantially. The bedrock beneath the till is fluted parallel to flow, with flutes that are 10–13 m deep by 200–1000 m wide; we believe these flutes are formed by erosion beneath a deforming till. We also observe an angular unconformity at the base of the till, which is consistent with the idea that erosion is occurring there. The sedimentary record in the Ross Embayment looks very similar to that beneath Ice Stream B, i.e. a few meters of till resting unconformably (the Ross Sea unconformity) on lithified sedimentary rock, and we postulate that the Ross Sea unconformity was generated by erosion beneath a grounded ice sheet by a deforming till.

scholarly journals Data-Driven Inference of the Mechanics of Slip Along Glacier Beds Using Physics-Informed Neural Networks

2021 ◽  
Author(s):  
Bryan Riel ◽  
Brent Minchew ◽  
Tobias Bischoff
Keyword(s):  
Neural Networks ◽  
Remote Sensing Data ◽  
Time Dependent ◽  
Surface Velocity ◽  
Time Varying ◽  
Ice Flow ◽  
Physical Constraints ◽  
Training Strategy ◽  
Proper Form ◽  
Ice Surface

<p>Reliable projections of sea level rise depend on accurate representations of how fast-flowing glaciers slip along their beds. Specifically, ice sheet models require a quantitative sliding law that relates basal drag to sliding velocity and glacier geometry, yet the proper form of the law remains uncertain. Here, we present a novel deep learning-based framework for learning the time evolution of basal drag from time-dependent ice surface velocity and elevation observations. We train a pair of probabilistic neural networks through a combination of time-dependent surface observations, governing equations for ice flow, and known physical constraints. Neural network outputs are stochastic predictions of time-varying basal drag that do not require any prior assumptions on the form of the sliding law. This training strategy is well-suited to large volumes of remote sensing data while providing a natural way to integrate our existing understanding of the physics of ice flow into the learning process.</p><p>We test this framework on 1D and 2D ice flow simulations and demonstrate that, under certain stress conditions, recovery of the underlying sliding law parameters and their uncertainties can be derived from the stochastic predictions of time-varying basal drag. We also apply these methods to Rutford Ice Stream and Pine Island Glacier in Antarctica to investigate subglacial hydrological effects for the former and evidence for regularized Coulomb sliding for the latter.</p>

scholarly journals The Dynamics of Austfonna, Nordaustlandet, Svalbard: Surface Velocities, Mass Balance, and Subglacial Melt Water

1989 ◽  
Vol 12 ◽  
pp. 37-45 ◽  
Author(s):  
Julian A. Dowdeswell ◽  
David J. Drewry
Keyword(s):  
Strain Rate ◽  
Mass Balance ◽  
Sea Level ◽  
Drainage Basin ◽  
Landsat Imagery ◽  
Lower Boundary ◽  
Surface Velocity ◽  
Ice Cap ◽  
Ice Surface ◽  
Melt Water

Glaciological measurements from Austfonna on Nordaustlandet, Svalbard, are needed as a prerequisite to mathematical modelling of ice-mass dynamics. Several upper and lower boundary conditions are set out in detail for a 670 km2 drainage basin (Basin 5) and are generalized to the whole ice cap where possible. The ice surface and bed topography are mapped for Basin 5. 30% of the basin lies below sea-level. Bed elevations range from -100 m to over 300 m, and maximum ice thickness is >500 m. A 21 km long trilateral network of stakes provides velocity and strain-rate data. Maximum ice-surface velocity is 47 m a−1 and maximum strain-rate is 0.64 × 10−2 a−1. Snow-line migration with time is mapped from digital Landsat MSS data, and mass-balance estimates are used to calculate balance velocities. At the equilibrium line, about 300–350 m in elevation, balance velocity and observed ice-surface velocity are comparable, indicating that the basin is approximately in balance. A first approximation is given for the rate of iceberg calving from the tide-water basin margins. Enhanced Landsat imagery also shows that turbid melt-water plumes of subglacial origin flow from the terminal ice cliffs, indicating that at least parts of the ice-cap margin are at the melting point. The margins of Basin 5, grounded below present sea-level, are likely to be underlain by deformable sediments, but inland the nature of the substrate is unknown.

scholarly journals ERS SAR feature-tracking measurement of outlet glacier velocities on a regional scale in East Greenland

2003 ◽  
Vol 36 ◽  
pp. 129-134 ◽  
Author(s):  
Adrian Luckman ◽  
Tavi Murray ◽  
Hester Jiskoot ◽  
Hamish Pritchard ◽  
Tazio Strozzi
Keyword(s):  
Feature Tracking ◽  
Regional Scale ◽  
Surface Velocity ◽  
Ice Flow ◽  
Outlet Glacier ◽  
East Greenland ◽  
Ice Surface ◽  
Fast Ice ◽  
Regional Basis ◽  
Ice Velocity

AbstractFeature tracking, or patch intensity cross-correlation, is used to derive two-dimensional ice-surface velocity fields from 1day and 35 day repeat-pass European Remote-sensing Satellite (ERS) synthetic aperture radar (SAR) data covering a 500 km by 500 km area of central East Greenland. Over regions of fast ice flow, 35 day tracking yields only a slightly lower density of velocity measurements than 1day tracking, and both are broadly in agreement about the spatial pattern of ice velocity except at the glacier termini where tidal effects may dominate. This study suggests that SAR feature tracking may be used to routinely monitor ice-discharge velocities on a regional basis and thereby inform studies of regional mass balance.

Velocities of the Amery Ice Shelf's primary tributary glaciers, 2004–12

2015 ◽  
Vol 27 (5) ◽  
pp. 511-523 ◽  
Author(s):  
M.L. Pittard ◽  
J.L. Roberts ◽  
C.S. Watson ◽  
B.K. Galton-Fenzi ◽  
R.C. Warner ◽  
...  
Keyword(s):  
Surface Velocity ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Shelves ◽  
Ice Surface ◽  
Amery Ice Shelf ◽  
Landsat 7 ◽  
One Year ◽  
Shelf Region

AbstractMonitoring the rate of ice flow into ice shelves is vital to understanding how, where and when mass changes occur in Antarctica. Previous observations of ice surface velocity indicate that the Amery Ice Shelf and tributary glaciers have been relatively stable over the period 1968 to 1999. This study measured the displacement of features on the ice surface over a sequence of Landsat 7 images separated by approximately one year and spanning 2004 to 2012 using the surface feature tracking software IMCORR. The focus is on the region surrounding the southern grounding zone of the Amery Ice Shelf and its primary tributary glaciers: the Fisher, Lambert and Mellor glaciers. No significant changes in surface velocity were observed over this period. Accordingly, the velocity fields from each image pair between 2004 and 2012 were used to synthesize an average velocity dataset of the Amery Ice Shelf region and to compare it to previously published velocity datasets and in situ global positioning system velocity observations. No significant change in ice surface velocities was found between 2004 and 2012 in the Amery Ice Shelf region, which suggests that it continues to remain stable.

scholarly journals The marginal shear stress of Ice Stream B, West Antarctica

1997 ◽  
Vol 43 (145) ◽  
pp. 415-426 ◽  
Author(s):  
Miriam Jackson ◽  
Barclay Kamb
Keyword(s):  
Shear Stress ◽  
Strain Rate ◽  
Time Scale ◽  
Shear Zones ◽  
Hot Water ◽  
West Antarctica ◽  
Ice Stream ◽  
Flow Law ◽  
Ice Stream B

AbstractTo ascertain whether the velocity of Ice Stream B, West Antarctica, may be controlled by the stresses in its marginal shear zones (the “Snake” and the “Dragon”), we undertook a determination of the marginal shear stress in the Dragon near Camp Up B by using ice itself as a stress meter. The observed marginal shear strain rate of 0.14 a−1is used to calculate the marginal shear stress from the flow law of ice determined by creep tests on ice cores from a depth of 300 m in the Dragon, obtained by using a hot-water ice-coring drill. The test-specimen orientation relative to the stress axes in the tests is chosen on the basis ofc-axis fabrics so that the test applies horizontal shear across vertical planes parallel to the margin. The resulting marginal shear stress is (2.2 ± 0.3) × 105Pa. This implies that 63–100% of the ice stream’s support against gravitational loading comes from the margins and only 37–0% from the base, so that the margins play an important role in controlling the ice-stream motion. The marginal shear-stress value is twice that given by the ice-stream model of Echelmeyer and others (1994) and the corresponding strain-rate enhancement factors differ greatly (E≈ 1–2 vs 10–12.5). This large discrepancy could be explained by recrystallization of the ice during or shortly after coring. Estimates of the expected recrystallization time-scale bracket the ∼1 h time-scale of coring and leave the likelihood of recrystallization uncertain. However, the observed two-maximum fabric type is not what is expected for annealing recrystallization from the sharp single-maximum fabric that would be expected in situ at the high shear strains involved (γ ∼ 20). Experimental data from Wilson (1982) suggest that, if the core did recrystallize, the prior fabric was a two-maximum fabric not substantially different from the observed one, which implies that the measured flow law and derived marginal shear stress are applicable to the in situ situation. These issues need to be resolved by further work to obtain a more definitive observational assessment of the marginal shear stress.

scholarly journals Acceleration of Pine Island and Thwaites Glaciers, West Antarctica

2002 ◽  
Vol 34 ◽  
pp. 189-194 ◽  
Author(s):  
Eric Rignot ◽  
David G. Vaughan ◽  
Marjorie Schmeltz ◽  
Todd Dupont ◽  
Douglas Macayeal
Keyword(s):  
Mass Loss ◽  
Sea Level ◽  
Radar Interferometry ◽  
Constant Flow ◽  
West Antarctica ◽  
Ice Flow ◽  
Ice Surface ◽  
Grounding Line ◽  
Satellite Radar ◽  
Global Sea Level

AbstractRecent satellite investigations revealed that in the 1990s the grounding line of Pine Island and Thwaites Glaciers, West Antarctica, retreated several km, the ice surface on the interior of the basins lowered 10 cm a–1, and Pine Island Glacier thinned 1.6 ma–1. These observations, however, were not sufficient to determine the cause of the changes. Here, we present satellite radar interferometry data that show the thinning and retreat of Pine Island Glacier are caused by an acceleration of ice flow of about 18 ± 2% in 8 years. Thwaites Glacier maintained a nearly constant flow regime at its center, but widened along the sides, and increased its 30 ± 15% mass deficit by another 4% in 4 years. The combined mass loss from both glaciers, if correct, contributes an estimated 0.08 ± 0.03 mma–1 global sea-level rise in 2000.

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