scholarly journals Greenland ice-sheet wide glacier classification based on two distinct seasonal ice velocity behaviors

2021 ◽  
pp. 1-8
Author(s):  
Saurabh Vijay ◽  
Michalea D. King ◽  
Ian M. Howat ◽  
Anne M. Solgaard ◽  
Shfaqat Abbas Khan ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Radar Data ◽  
The South ◽  
Drainage Systems ◽  
Northern Regions ◽  
Ice Velocity ◽  
Glacier Flow ◽  
Type 3

Abstract Greenland glaciers exhibit variable seasonal velocity signals that may reflect differences in subglacial hydrology. Here, we conduct a first GrIS-wide glacier classification based on seasonal velocity patterns derived from 2017 Sentinel-1 radar data. Our classification focuses on two distinct seasonal ice velocity patterns, with the first (type-2 from Moon and others, 2014) showing periods of both speedup and slowdown during the melt season, and the second (type-3) instead showing a longer period of slowdown from elevated velocities in the winter and spring. We analyze 221 glaciers in 2017 and show that 48 exhibit type-2 behavior, and 72 exhibit type-3 behavior. We extend the classification to 2018 and 2019 and find that while the glaciers meeting each criterion vary year to year, type-2 is consistently more common in the northern regions and type-3 is more common in the south. Our results highlight the varied impact of meltwater on subglacial drainage systems and glacier flow in Greenland.

scholarly journals Greenland ice velocity maps from the PROMICE project

2021 ◽  
Vol 13 (7) ◽  
pp. 3491-3512
Author(s):  
Anne Solgaard ◽  
Anders Kusk ◽  
John Peter Merryman Boncori ◽  
Jørgen Dall ◽  
Kenneth D. Mankoff ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Radar Data ◽  
Temporal Consistency ◽  
Gps Measurements ◽  
High Accumulation ◽  
Synthetic Aperture Radar Data ◽  
Spatial Coverage ◽  
Ice Velocity ◽  
The Difference

Abstract. We present the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) Ice Velocity product (https://doi.org/10.22008/promice/data/sentinel1icevelocity/greenlandicesheet, Solgaard and Kusk, 2021), which is a time series of Greenland Ice Sheet ice velocity mosaics spanning September 2016 through to the present. The product is based on Sentinel-1 synthetic aperture radar data and has a 500 m grid spacing. A new mosaic is available every 12 d and spans two consecutive Sentinel-1 cycles (24 d). The product is made available within ∼ 10 d of the last acquisition and includes all possible 6 and 12 d pairs within the two Sentinel-1A cycles. We describe our operational processing chain from data selection, mosaicking, and error estimation to final outlier removal. The product is validated against in situ GPS measurements. We find that the standard deviation of the difference between satellite- and GPS-derived velocities (and bias) is 20 m yr−1 (−3 m yr−1) and 27 m yr−1 (−2 m yr−1) for the components in an eastern and northern direction, respectively. Over stable ground the values are 8 m yr−1 (0.1 m yr−1) and 12 m yr−1 (−0.6 m yr−1) in an eastern and northern direction, respectively. This is within the expected values; however, we expect that the GPS measurements carry a considerable part of this uncertainty. We investigate variations in coverage from both a temporal and spatial perspective. The best spatial coverage is achieved in winter due to the comprehensive data coverage by Sentinel-1 and high coherence, while summer mosaics have the lowest coverage due to widespread melt. The southeast Greenland Ice Sheet margin, along with other areas of high accumulation and melt, often has gaps in the ice velocity mosaics. The spatial comprehensiveness and temporal consistency make the product ideal both for monitoring and for studying ice-sheet-wide and glacier-specific ice discharge and dynamics of glaciers on seasonal scales.

scholarly journals Greenland flow variability from ice-sheet-wide velocity mapping

2010 ◽  
Vol 56 (197) ◽  
pp. 415-430 ◽  
Author(s):  
Ian Joughin ◽  
Ben E. Smith ◽  
Ian M. Howat ◽  
Ted Scambos ◽  
Twila Moon
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Radar Data ◽  
Synthetic Aperture ◽  
Velocity Mapping ◽  
Outlet Glacier ◽  
Synthetic Aperture Radar Data ◽  
Bedrock Topography ◽  
Speed Up ◽  
Glacier Flow

AbstractUsing RADARSAT synthetic aperture radar data, we have mapped the flow velocity over much of the Greenland ice sheet for the winters of 2000/01 and 2005/06. These maps provide a detailed view of the ice-sheet flow, including that of the hundreds of glaciers draining the interior. The focused patterns of flow at the coast suggest a strong influence of bedrock topography. Differences between our two maps confirm numerous early observations of accelerated outlet glacier flow as well as revealing previously unrecognized changes. The overall pattern is one of speed-up accompanied by terminus retreat, but there are also several instances of surge behavior and a few cases of glacier slowdown. Comprehensive mappings such as these, at regular intervals, provide an important new observational capability for understanding ice-sheet variability.

scholarly journals Greenland ice velocity maps from the PROMICE project

2021 ◽  
Author(s):  
Anne Solgaard ◽  
Anders Kusk ◽  
John Peter Merryman Boncori ◽  
Jørgen Dall ◽  
Kenneth D. Mankoff ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Radar Data ◽  
Temporal Consistency ◽  
Gps Measurements ◽  
High Accumulation ◽  
Synthetic Aperture Radar Data ◽  
Spatial Coverage ◽  
Ice Velocity ◽  
The Difference

Abstract. We present the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) ice velocity product (https://doi.org/10.22008/promice/data/sentinel1icevelocity/greenlandicesheet) (Solgaard and Kusk, 2021)) which is a September 2016 through present time series of Greenland Ice Sheet ice-velocity mosaics. The product is based on Sentinel-1 synthetic aperture radar data and has a 500 m spatial resolution. A new mosaic is available every 12 days and span two consecutive Sentinel-1 cycles (24 days). The product is made available within ~10 days of the last acquisition and includes all possible 6 and 12 day pairs within the two Sentinel-1A cycles. We describe our operational processing chain in high detail from data selection, mosaicking and error estimation to final outlier removal. The product is validated against in-situ GPS measurements. We find that the standard deviation of the difference between satellite and GPS derived velocities is 20 m/yr and 27 m/yr for the vx and vy components, respectively. This is within the expected bounds, however, we expect that the GPS measurements carry a considerable part of this uncertainty. We investigate variations in coverage from both a temporal and spatial perspective. Best spatial coverage is achieved in winter due to excellent data coverage and high coherence, while summer mosaics have the lowest coverage due to widespread melt. The southeast Greenland Ice Sheet margin, along with other areas of high accumulation and melt, often have gaps in the ice velocity mosaics. The spatial comprehensiveness and temporal consistency make the product ideal for monitoring and studying ice-sheet wide ice discharge and dynamics of glaciers.

scholarly journals A new bedrock and surface elevation dataset for modelling the Greenland ice sheet

2003 ◽  
Vol 37 ◽  
pp. 351-356 ◽  
Author(s):  
Jonathan L. Bamber ◽  
Duncan J. Baldwin ◽  
S. Prasad Gogineni
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Detailed Comparison ◽  
Radar Data ◽  
The Arctic ◽  
Small Scale ◽  
Surface Model ◽  
Rock Outcrops ◽  
Bed Topography ◽  
Elevation Model

AbstractA new digital elevation model of the surface of the Greenland ice sheet and surrounding rock outcrops has been produced from a comprehensive suite of satellite and airborne remote-sensing and cartographic datasets. The surface model has been regridded to a resolution of 5 km, and combined with a new ice-thickness grid derived from ice-penetrating radar data collected in the 1970s and 1990s. A further dataset, the International Bathymetric Chart of the Arctic Ocean, was used to extend the bed elevations to include the continental shelf. The new bed topography was compared with a previous version used for ice-sheet modelling. Near the margins of the ice sheet and, in particular, in the vicinity of small-scale features associated with outlet glaciers and rapid ice motion, significant differences were noted. This was highlighted by a detailed comparison of the bed topography around the northeast Greenland ice stream.

scholarly journals Oceanic heat delivery via Kangerdlugssuaq Fjord to the south-east Greenland ice sheet

2014 ◽  
Vol 119 (2) ◽  
pp. 631-645 ◽  
Author(s):  
Mark E. Inall ◽  
Tavi Murray ◽  
Finlo R. Cottier ◽  
Kilian Scharrer ◽  
Timothy J. Boyd ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
The South ◽  
East Greenland

scholarly journals Assessing ice margin fluctuations on differing timescales: Chronological constraints from Sermeq Kujatdleq and Nordenskiöld Gletscher, central West Greenland

The Holocene ◽  
2018 ◽  
Vol 28 (7) ◽  
pp. 1160-1172 ◽  
Author(s):  
Samuel E Kelley ◽  
Jason P Briner ◽  
Sandy L O’Hara
Keyword(s):  
Late Holocene ◽  
Sediment Cores ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Dynamics ◽  
West Greenland ◽  
Southern Site ◽  
Ice Velocity ◽  
Observational Record ◽  
Local Variability

The observational record of ice margin position reveals asynchrony in both the timing and magnitude of Greenland Ice Sheet (GrIS) margin fluctuations and illustrates the complex reactions of ice sheets to climatic perturbations. In this study, we reconstruct the timing and pattern of middle- and late-Holocene GrIS margin fluctuations at two locations, ~190 km apart, in central West Greenland using radiocarbon-dated sediment cores from proglacial-threshold lakes. Our results demonstrate that deglaciation occurs at both sites during the early Holocene, with the ice sheet remaining in a smaller-than-present ice margin configuration until ~500 years ago when it readvanced into lake catchments at both sites. At our northern site, Sermeq Kujatdleq, the late-Holocene advance of the GrIS approached maximum position during the past 280 years, with the culmination of the advance occurring at AD 1992–1994, and modern retreat was underway by AD 1998–2001. In contrast, field and observational evidence suggest that the GrIS at our southern site, Nordenskiöld Gletscher, has been advancing or stable throughout the 20th century. These results, in conjunction with previous work in the region, highlight the asynchronous nature of late-Holocene advances and subsequent modern retreat, implying that local variability, such as ice velocity or ice dynamics, is responsible for modulating ice margin response to changes in climate on these decadal to centennial timescales. Additional high-resolution records of past ice sheet fluctuations are needed to inform and more accurately constrain our predictions of future cryosphere response to changes in climate.

scholarly journals Quantitative estimates of velocity sensitivity to surface melt variations at a large Greenland outlet glacier

2011 ◽  
Vol 57 (204) ◽  
pp. 609-620 ◽  
Author(s):  
M.L. Andersen ◽  
M. Nettles ◽  
P. Elosegui ◽  
T.B. Larsen ◽  
G.S. Hamilton ◽  
...  
Keyword(s):  
Fluid Pressure ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Absolute Magnitude ◽  
Flow Speed ◽  
Relative Importance ◽  
Outlet Glacier ◽  
Quantitative Estimates ◽  
Surface Melt ◽  
Glacier Flow

AbstractThe flow speed of Greenland outlet glaciers is governed by several factors, the relative importance of which is poorly understood. The delivery of surface-generated meltwater to the bed of alpine glaciers has been shown to influence glacier flow speed when the volume of water is sufficient to increase basal fluid pressure and hence basal lubrication. While this effect has also been demonstrated on the Greenland ice-sheet margin, little is known about the influence of surface melting on the large, marine-terminating outlet glaciers that drain the ice sheet. We use a validated model of meltwater input and GPS-derived surface velocities to quantify the sensitivity of glacier flow speed to changes in surface melt at Helheim Glacier during two summer seasons (2007–08). Our observations span ∼55 days near the middle of each melt season. We find that relative changes in glacier speed due to meltwater input are small, with variations of ∼45% in melt producing changes in velocity of ∼2–4%. These velocity variations are, however, of similar absolute magnitude to those observed at smaller glaciers and on the ice-sheet margin. We find that the glacier’s sensitivity to variations in meltwater input decreases approximately exponentially with distance from the calving front. Sensitivity to melt varies with time, but generally increases as the melt season progresses. We interpret the time-varying sensitivity of glacier flow to meltwater input as resulting from changes in subglacial hydraulic routing caused by the changing volume of meltwater input.

scholarly journals Processing methodology for the ITS_LIVE Sentinel-1 ice velocity product

2021 ◽  
Author(s):  
Yang Lei ◽  
Alex S. Gardner ◽  
Piyush Agram
Keyword(s):  
Ice Sheet ◽  
Radar Data ◽  
Electron Content ◽  
Image Pair ◽  
Total Electron ◽  
Velocity Inversion ◽  
Slant Range ◽  
Ice Velocity ◽  
Image Pairs ◽  
Offset Tracking

Abstract. The NASA MEaSUREs Inter-mission Time Series of Land Ice Velocity and Elevation (ITS_LIVE) project seeks to accelerate understanding of critical glaciers and ice sheet processes by providing researchers with global, low-latency, comprehensive and state-of-the-art records of surface velocities and elevations as observed from space. Here we describe the image-pair ice velocity product and processing methodology for ESA Sentinel-1 radar data. We demonstrate improvements to the core processing algorithm for dense offset tracking, “autoRIFT”, that provides finer resolution and higher accuracy data products with improved computational efficiency when compared to earlier versions. A novel calibration is applied to the data to correct for Sentinel-1A/B subswath- and full swath-dependent geolocation errors caused by systematic issues with the instruments. Sentinel-1’s C-band images are affected by variations in the total electron content of the ionosphere that results in large velocity errors in the azimuth (along-track) direction. To reduce these effects slant-range (line-of-sight or LOS) velocities are used and accompanied by LOS parameters that support map coordinate (x/y) velocity inversion from ascending and descending slant-range offset measurements, as derived from 2 image-pairs. The described product and methods comprise the MEaSUREs ITS_LIVE Sentinel-1 Image-Pair Glacier and Ice Sheet Surface Velocities: Version 2 (https://its-live.jpl.nasa.gov).

scholarly journals Ice-Penetrating Radar Reveals Age of Greenland Ice Sheet Layers

Eos ◽  
2015 ◽  
Vol 96 ◽  
Author(s):  
Terri Cook
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Radar Data ◽  
Comprehensive Analysis ◽  
History Of ◽  
Insight Into

First comprehensive analysis of deep radar data gives insight into the dynamics and history of the Greenland Ice Sheet.

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