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 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 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-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 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 Seasonal mass variations show timing and magnitude of meltwater storage in the Greenland Ice Sheet

2018 ◽  
Vol 12 (9) ◽  
pp. 2981-2999 ◽  
Author(s):  
Jiangjun Ran ◽  
Miren Vizcaino ◽  
Pavel Ditmar ◽  
Michiel R. van den Broeke ◽  
Twila Moon ◽  
...  
Keyword(s):  
Mass Balance ◽  
Climate Model ◽  
Spatial Scales ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Mass Balance ◽  
High Accumulation ◽  
Outlet Glacier ◽  
Surface Mass ◽  
Meltwater Runoff

Abstract. The Greenland Ice Sheet (GrIS) is currently losing ice mass. In order to accurately predict future sea level rise, the mechanisms driving the observed mass loss must be better understood. Here, we combine data from the satellite gravimetry mission Gravity Recovery and Climate Experiment (GRACE), surface mass balance (SMB) output of the Regional Atmospheric Climate Model v. 2 (RACMO2), and ice discharge estimates to analyze the mass budget of Greenland at various temporal and spatial scales. We find that the mean rate of mass variations in Greenland observed by GRACE was between −277 and −269 Gt yr−1 in 2003–2012. This estimate is consistent with the sum (i.e., -304±126 Gt yr−1) of individual contributions – surface mass balance (SMB, 216±122 Gt yr−1) and ice discharge (520±31 Gt yr−1) – and with previous studies. We further identify a seasonal mass anomaly throughout the GRACE record that peaks in July at 80–120 Gt and which we interpret to be due to a combination of englacial and subglacial water storage generated by summer surface melting. The robustness of this estimate is demonstrated by using both different GRACE-based solutions and different meltwater runoff estimates (namely, RACMO2.3, SNOWPACK, and MAR3.9). Meltwater storage in the ice sheet occurs primarily due to storage in the high-accumulation regions of the southeast and northwest parts of Greenland. Analysis of seasonal variations in outlet glacier discharge shows that the contribution of ice discharge to the observed signal is minor (at the level of only a few gigatonnes) and does not explain the seasonal differences between the total mass and SMB signals. With the improved quantification of meltwater storage at the seasonal scale, we highlight its importance for understanding glacio-hydrological processes and their contributions to the ice sheet mass variability.

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 Relationships between interannual variability of glacier mass balance and climate

1999 ◽  
Vol 45 (151) ◽  
pp. 456-462 ◽  
Author(s):  
Roger J. Braithwaite ◽  
Yu Zhang
Keyword(s):  
Standard Deviation ◽  
Mass Balance ◽  
Interannual Variability ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
The Arctic ◽  
Glacier Mass Balance ◽  
Strongly Correlated ◽  
Calculated Mass ◽  
The Difference

AbstractThe interannual variability of glacier mass balance is expressed by the standard deviation of net balance, which varies from about ±0.1 to ±1.4 m a−1for a sample of 115 glaciers with at least 5 years of record. The standard deviation of net balance is strongly correlated with the mass-balance amplitude (half the difference between winter and summer balances) for 60 glaciers, so the amplitude can be estimated from net balance standard deviation for the other 55 glaciers where winter and summer balances are unavailable. The observed and calculated mass-balance amplitudes for the 115 glaciers show contrasts between the Arctic and lower latitudes, and between maritime and continental regions. The interannual variability of mass balance means that balances must be measured for at least a few years to determine a statistically reliable mean balance for any glacier. The net balance of the Greenland ice sheet is still not accurately known, but its standard deviation is here estimated to be about ±0.24 m a−1, in agreement with other Arctic glaciers. Mass-balance variability of this magnitude implies that the ice sheet can thicken or thin by several metres over 20–30 years without giving statistically significant evidence of non-zero balance under present climate.

scholarly journals Sensitivity of the frozen/melted basal boundary to perturbations of basal traction and geothermal heat flux: Isunnguata Sermia, western Greenland

2011 ◽  
Vol 52 (59) ◽  
pp. 43-50 ◽  
Author(s):  
Douglas J. Brinkerhoff ◽  
Toby W. Meierbachtol ◽  
Jesse V. Johnson ◽  
Joel T. Harper
Keyword(s):  
Heat Flux ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Thermal Conditions ◽  
Two Dimensional ◽  
Adjoint Model ◽  
The West ◽  
Geothermal Heat ◽  
Coupled Numerical Model ◽  
The Difference

AbstractA full-stress, thermomechanically coupled, numerical model is used to explore the interaction between basal thermal conditions and motion of a terrestrially terminating section of the west Greenland ice sheet. The model domain is a two-dimensional flowline profile extending from the ice divide to the margin. We use data-assimilation techniques based on the adjoint model in order to optimize the basal traction field, minimizing the difference between modeled and observed surface velocities. We monitor the sensitivity of the frozen/melted boundary (FMB) to changes in prescribed geothermal heat flux and sliding speed by applying perturbations to each of these parameters. The FMB shows sensitivity to the prescribed geothermal heat flux below an upper threshold where a maximum portion of the bed is already melted. The position of the FMB is insensitive to perturbations applied to the basal traction field. This insensitivity is due to the short distances over which longitudinal stresses act in an ice sheet.

scholarly journals Seasonal variation of ice ablation at the margin of the Greenland ice sheet and its sensitivity to climate change, Qamanârssûp sermia, West Greenland

1993 ◽  
Vol 39 (132) ◽  
pp. 267-274 ◽  
Author(s):  
Roger J. Braithwaite ◽  
Ole Β. Olesen
Keyword(s):  
Climate Change ◽  
Seasonal Variation ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Seasonal Distribution ◽  
Future Climate Change ◽  
Temperature Model ◽  
Present Climate ◽  
The Difference ◽  
June July

AbstractMonthly ice ablation was measured at the margin of the Greenland ice sheet for June, July and August over 7 years (1980–86). The total winter ablation (September-May) has also been measured, and a simple ablation-temperature model used to assign ablation values to individual months. Under the present climate, the most ablation occurred in June-August (on average 81% of annual ablation), moderate ablation took place in May and September (17%) and very little ablation occurred in October-April (2%). The effect of climate change on ice ablation is simulated using the ablation model to recalculate ablation for higher temperatures. Summer ice ablation increases with temperature in the model, but there is proportionally greater increase for May and September, whereas the period from October to April is presently so cold that even a temperature rise of +5 °C will hardly increase ablation. The difference in annual ice ablation caused by future climate change will therefore depend upon the seasonal distribution of the temperature change. Changes in precipitation and accumulation will further modify the seasonal variation of ablation.

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).

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