A complete map of Greenland ice velocity derived from satellite data collected over 20 years

ABSTRACTWhile numerous maps of Greenland ice flow velocity exist, most have gaps in coverage and/or accuracy is limited. We processed a large volume of synthetic aperture radar and Landsat 8 imagery collected between 1995 and 2015 to produce a nearly complete map of ice flow velocity for Greenland at a far greater accuracy than most prior products. We evaluated the accuracy of this map by comparing it with a variety of measured and estimated velocities. For the slow-moving interior of the ice sheet, where estimates are determined from interferometric phase, the errors are ~2 m a−1 or better. For coastal areas, where estimates are determined entirely from speckle- or feature-tracking methods, errors are 2–3 m a−1, which is in good agreement with the estimated formal errors. Especially for the slow-moving majority of the ice sheet, this map provides an important source of data for numerous types of glaciological studies.

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Greenland Ice Mapping Project: Ice Flow Velocity Variation at submonthly to decadal time scales

10.5194/tc-2018-40 ◽

2018 ◽

Author(s):

Ian Joughin ◽

Ben E. Smith ◽

Ian Howat

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Velocity Variation ◽

Landsat 8 ◽

Ice Flow ◽

Speed Up ◽

Ice Velocity ◽

Year 2000 ◽

The Impact ◽

Ice Sheet Mapping

Abstract. We describe several new ice velocity maps produced by the Greenland Ice Sheet Mapping Project (GIMP) using Landsat 8 and Copernicus Sentinel 1A/B data. We then focus on several sites where we analyse these data in conjunction with earlier data from this project, which extend back to the year 2000. At Jakobshavn Isbrae and Koge Bugt, we find good agreement when comparing results from different sensors. In a change from recent behaviour, Jakobshavn Isbrae began slowing substantially in 2017, with a mid-summer peak that was even slower than some previous winter minimums. Over the last decade, we identify two major slowdown events at Koge Bugt that coincide with short-term advances of the terminus. We also examined populations of glaciers in northwest and southwest Greenland to produce a record of speedup since 2000. Collectively these glaciers continue to speed up, but there are regional differences in the timing of periods of peak speedup. In addition, we computed trends for much of the southwest margin of the ice sheet where other work has suggested slowing ice flow in response to increased melting. Contrary to the earlier results, we find no evidence for a slowdown distributed over a wide area. Finally, although consistency of the data generally is good through time and across sensors, our analysis indicates substantial differences can arise in regions with high strain rates (e.g., shear margins) where sensor resolution can become a factor. For applications such as constraining model inversions, users should factor in the impact that the data's resolution has on their results.

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Antarctic Ice-Sheet Topography and Surface-Bedrock Relationships

Annals of Glaciology ◽

10.1017/s0260305500001282 ◽

1986 ◽

Vol 8 ◽

pp. 124-128 ◽

Cited By ~ 14

Author(s):

N.F. McIntyre

Keyword(s):

Three Dimensional ◽

Ice Sheet ◽

Coastal Regions ◽

Three Dimensional Flow ◽

Ice Flow ◽

Antarctic Ice Sheet ◽

Dimensional Flow ◽

Ice Velocity ◽

The Antarctic ◽

Ice Sheet Topography

Mapping the topography of the Antarctic ice sheet has confirmed that there is, typically, a decrease in the wavelength and increase in the amplitude of surface undulations with distance from ice divides. This pattern is distorted by converging ice flow in coastal regions and by other variations in subglacial relief, ice velocity, and viscosity. The near-symmetry of undulations indicates the extent of three-dimensional flow over bedrock peaks. Spectral analyses indicate the greater response of the ice sheet to bedrock features with longer wavelengths. This is affected, and in some cases dominated, by the inhomogeneous and non-isothermal nature of the ice sheet.

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Formational history of the Wicklow Trough: a marine‐transgressed tunnel valley revealing ice flow velocity and retreat rates for the largest ice stream draining the late‐Devensian British–Irish Ice Sheet

Journal of Quaternary Science ◽

10.1002/jqs.3234 ◽

2020 ◽

Vol 35 (7) ◽

pp. 907-919 ◽

Cited By ~ 1

Author(s):

Mark Coughlan ◽

Zsuzsanna TÓth ◽

Katrien J. J. Van Landeghem ◽

Stephen Mccarron ◽

Andrew J. Wheeler

Keyword(s):

Flow Velocity ◽

Ice Sheet ◽

Ice Flow ◽

Ice Stream ◽

History Of

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Seasonal to multi-annual speedup and slowdown of Greenland outlet glaciers inferred from time-dependent remote sensing observations

10.5194/egusphere-egu2020-12679 ◽

2020 ◽

Author(s):

Lizz Ultee ◽

Bryan Riel ◽

Brent Minchew

Keyword(s):

Time Series ◽

Flow Velocity ◽

Ice Sheet ◽

Surface Air Temperature ◽

Greenland Ice Sheet ◽

Time Dependent ◽

Surface Velocity ◽

Short Term ◽

Ice Flow

<p>The rate of ice flux from the Greenland Ice Sheet to the ocean depends on the ice flow velocity through outlet glaciers. Ice flow velocity, in turn, evolves in response to multiple geographic and environmental forcings at different timescales. For example, velocity may vary daily in response to ocean tides, seasonally in response to surface air temperature, and multi-annually in response to long-term trends in climate. The satellite observations processed as part of the NASA MEaSUREs Greenland Ice Sheet Velocity Map allow us to analyse variations in ice surface velocity at multiple timescales. Here, we decompose short-term and long-term signals in time-dependent velocity fields for Greenland outlet glaciers based on the methods of Riel et al. (2018). Patterns found in short-term signals can constrain basal sliding relations and ice rheology, while the longer-term signals hint at decadal in/stability of outlet glaciers. We present example velocity time series for outlets including Sermeq Kujalleq (Jakobshavn Isbrae) and Helheim Glacier, and we highlight features indicative of dynamic drawdown or advective restabilization. Finally, we comment on the capabilities of a time series analysis software under development for glaciological applications.</p>

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Using ice-flow models to evaluate potential sites of million year-old ice in Antarctica

Climate of the Past Discussions ◽

10.5194/cpd-9-2859-2013 ◽

2013 ◽

Vol 9 (3) ◽

pp. 2859-2887 ◽

Cited By ~ 2

Author(s):

B. Van Liefferinge ◽

F. Pattyn

Keyword(s):

Ice Sheet ◽

Geothermal Heat ◽

Ice Flow ◽

Flow Models ◽

Drill Site ◽

Slow Moving ◽

Basal Melting ◽

The Antarctic ◽

Suitable Potential

Abstract. Finding suitable potential sites for an undisturbed record of million-year old ice in Antarctica requires a slow-moving ice sheet (preferably an ice divide) and basal conditions that are not disturbed by large topographic variations. Furthermore, ice should be thick and cold basal conditions should prevail, since basal melting would destroy the bottom layers. However, thick ice (needed to resolve the signal at sufficient high resolution) increases basal temperatures, which is a conflicting condition in view of finding a suitable drill site. In addition, slow moving areas in the center of ice sheets are also low-accumulation areas, and low accumulation reduces potential cooling of the ice through vertical advection. While boundary conditions such as ice thickness and accumulation rates are relatively well constraint, the major uncertainty in determining basal conditions resides in the geothermal heat flow (GHF) underneath the ice sheet. We explore uncertainties in existing GHF datasets and their effect on basal temperatures of the Antarctic ice sheet and propose an updated method based on Pattyn (2010) to improve existing GHF datasets in agreement with known basal temperatures and their gradients to reduce this uncertainty. Both complementary methods lead to a better comprehension of basal temperature sensitivity and a characterization of potential ice coring sites within these uncertainties.

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Increased West Antarctic ice discharge and East Antarctic stability over the last seven years

10.5194/tc-2017-75 ◽

2017 ◽

Cited By ~ 1

Author(s):

Alex S. Gardner ◽

Geir Moholdt ◽

Ted Scambos ◽

Mark Fahnstock ◽

Stefan Ligtenberg ◽

...

Keyword(s):

Synthetic Aperture Radar ◽

Sea Level Rise ◽

Sea Level ◽

Ice Sheets ◽

Synthetic Aperture ◽

Direct Role ◽

Ice Flow ◽

West Antarctic ◽

Landsat 7 ◽

Ice Velocity

Abstract. Ice discharge from large ice sheets plays a direct role in determining rates of sea level rise. We map present-day Antarctic-wide surface velocities using Landsat 7 & 8 imagery spanning 2013–2015 and compare to earlier estimates derived from synthetic aperture radar, revealing heterogeneous changes in ice flow since ~ 2008. The new mapping provides complete coastal and inland coverage of ice velocity with a mean error of

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Present-day high-resolution ice velocity map of the Antarctic ice sheet

10.5194/essd-2018-149 ◽

2018 ◽

Cited By ~ 1

Author(s):

Qiang Shen ◽

Hansheng Wang ◽

C. K. Shum ◽

Liming Jiang ◽

Hou Tse Hsu ◽

...

Keyword(s):

Sea Level ◽

Displacement Vector ◽

Ice Sheet ◽

Landsat 8 ◽

Ice Streams ◽

Coupled Models ◽

Ice Dynamics ◽

Antarctic Ice Sheet ◽

Ice Velocity ◽

The Antarctic

Abstract. Ice velocity constitutes a key parameter for estimating ice-sheet discharge rates and is crucial for improving coupled models of the Antarctic ice sheet to accurately predict its future fate and contribution to sea-level change. Here, we present a new Antarctic ice velocity map at a 100-m grid spacing inferred from Landsat 8 imagery data collected from December 2013 through March 2016 and robustly processed using the feature tracking method. These maps were assembled from over 73,000 displacement vector scenes inferred from over 32,800 optical images. Our maps cover nearly all the ice shelves, landfast ice, ice streams, and most of the ice sheet. The maps have an estimated uncertainty of less than 10 m yr-1 based on robust internal and external validations. These datasets will allow for a comprehensive continent-wide investigation of ice dynamics and mass balance combined with the existing and future ice velocity measurements and provide researchers access to better information for monitoring local changes in ice glaciers. Other uses of these datasets include control and calibration of ice-sheet modelling, developments in our understanding of Antarctic ice-sheet evolution, and improvements in the fidelity of projects investigating sea-level rise (https://doi.pangaea.de/10.1594/PANGAEA.895738).

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Greenland Ice Mapping Project: ice flow velocity variation at sub-monthly to decadal timescales

The Cryosphere ◽

10.5194/tc-12-2211-2018 ◽

2018 ◽

Vol 12 (7) ◽

pp. 2211-2227 ◽

Cited By ~ 20

Author(s):

Ian Joughin ◽

Ben E. Smith ◽

Ian Howat

Keyword(s):

Flow Speed ◽

Velocity Variation ◽

Landsat 8 ◽

North West ◽

South West ◽

Speed Up ◽

Ice Velocity ◽

Year 2000 ◽

The Impact ◽

Good Agreement

Abstract. We describe several new ice velocity maps produced by the Greenland Ice Mapping Project (GIMP) using Landsat 8 and Copernicus Sentinel 1A/B data. We then focus on several sites where we analyse these data in conjunction with earlier data from this project, which extend back to the year 2000. At Jakobshavn Isbræ and Køge Bugt, we find good agreement when comparing results from different sensors. In a change from recent behaviour, Jakobshavn Isbræ began slowing substantially in 2017, with a midsummer peak that was even slower than some previous winter minima. Over the last decade, we identify two major slowdown events at Køge Bugt that coincide with short-term advances of the terminus. We also examined populations of glaciers in north-west and south-west Greenland to produce a record of speed-up since 2000. Collectively these glaciers continue to speed up, but there are regional differences in the timing of periods of peak speed-up. In addition, we computed trends in winter flow speed for much of the south-west margin of the ice sheet and find little in the way of statistically significant changes over the period covered by our data. Finally, although the consistency of the data is generally good over time and across sensors, our analysis indicates that substantial differences can arise in regions with high strain rates (e.g. shear margins) where sensor resolution can become a factor. For applications such as constraining model inversions, users should factor in the impact that the data's resolution has on their results.

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The Equation of Continuity and its Application to the Ice Sheet Near “byrd” Station, Antarctica

Journal of Glaciology ◽

10.1017/s0022143000021055 ◽

1977 ◽

Vol 18 (80) ◽

pp. 359-371 ◽

Cited By ~ 49

Author(s):

I. M. Whillans

Keyword(s):

Steady State ◽

Mass Balance ◽

Ice Sheet ◽

Ice Thickness ◽

Surface Mass Balance ◽

Velocity Measurements ◽

Ice Flow ◽

Measured Velocity ◽

Surface Mass ◽

Ice Velocity

Abstract The continuity relationship that is often used in the study of ice sheets and ice shelves is developed by integrating the equation of continuity through the ice thickness. This equation is then integrated again with respect to horizontal distance from an ice divide, showing that the difference between the true ice velocity and the balance velocity, which is defined, is a measure of the time chance of the mass of a column through the ice thickness. The relationship is applied using data from along the “Byrd” station strain network, Antarctica. This region is found to be thinning slowly (0.03 m a−1 of ice of mean density) and uniformly, but it is still close to steady-state. The calculations would show a larger thinning rate if bottom sliding contributed more to the ice movement and integral shear contributed less, but the “Byrd” station bore-hole tilting results of Garfield and Ueda (1975, 1976), together with surface velocity measurements at “Byrd” station, indicate that most of the ice flow is by deformation within the ice mass. This large amount of internal deformation is more than that predicted by most “flow laws”, probably because of the strongly oriented ice-crystal fabric in the ice sheet. The cause of ice thinning is probably decreased surface mass balance beginning before A.D. 1550. The consistent relationship between measured velocity and balance velocity indicates that the ice flow is simple and that flow lines are in the same direction at depth as at the surface when considered smoothed over a distance of 10 km. Because the ice sheet is at present thinning, the balance velocity, calculated only from flow line and surface mass-balance data, and the somewhat mistaken assumption of steady-state is 15% less than the true ice velocity. This rather small difference confirms the use of balance-velocity estimates where velocity measurements are not available.

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

Annals of Glaciology ◽

10.3189/172756403781816428 ◽

2003 ◽

Vol 36 ◽

pp. 129-134 ◽

Cited By ~ 31

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.

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