Monthly Surface Elevation Changes of the Greenland Ice Sheet From ICESat-1, CryoSat-2, and ICESat-2 Altimetry Missions

AbstractChanges in ice-sheet surface elevation are caused by a combination of ice-dynamic imbalance, ablation, temporal variations in accumulation rate, firn compaction and underlying bedrock motion. Thus, deriving the rate of ice-sheet mass change from measured surface elevation change requires information on the rate of firn compaction and bedrock motion, which do not involve changes in mass, and requires an appropriate firn density to associate with elevation changes induced by recent accumulation rate variability. We use a 25 year record of surface temperature and a parameterization for accumulation change as a function of temperature to drive a firn compaction model. We apply this formulation to ICESat measurements of surface elevation change at three locations on the Greenland ice sheet in order to separate the accumulation-driven changes from the ice-dynamic/ablation-driven changes, and thus to derive the corresponding mass change. Our calculated densities for the accumulation-driven changes range from 410 to 610 kgm–3, which along with 900 kgm–3 for the dynamic/ablation-driven changes gives average densities ranging from 680 to 790 kgm–3. We show that using an average (or ‘effective’) density to convert elevation change to mass change is not valid where the accumulation and the dynamic elevation changes are of opposite sign.

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ESA's Ice Sheets CCI: validation and inter-comparison of surface elevation changes derived from laser and radar altimetry over Jakobshavn Isbræ, Greenland – Round Robin results

The Cryosphere Discussions ◽

10.5194/tcd-7-5433-2013 ◽

2013 ◽

Vol 7 (6) ◽

pp. 5433-5460

Author(s):

J. F. Levinsen ◽

K. Khvorostovsky ◽

F. Ticconi ◽

A. Shepherd ◽

R. Forsberg ◽

...

Keyword(s):

Drainage Basin ◽

European Space Agency ◽

Ice Sheets ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Round Robin ◽

Surface Elevation ◽

Optimal Method ◽

Radar Altimetry ◽

Elevation Changes

Abstract. In order to increase the understanding of the changing climate, the European Space Agency has launched the Climate Change Initiative (ESA CCI), a program which joins scientists and space agencies into 13 projects either affecting or affected by the concurrent changes. This work is part of the Ice Sheets CCI and four parameters are to be determined for the Greenland Ice Sheet (GrIS), each resulting in a dataset made available to the public: Surface Elevation Changes (SEC), surface velocities, grounding line locations, and calving front locations. All CCI projects have completed a so-called Round Robin exercise in which the scientific community was asked to provide their best estimate of the sought parameters as well as a feedback sheet describing their work. By inter-comparing and validating the results, obtained from research institutions world-wide, it is possible to develop the most optimal method for determining each parameter. This work describes the SEC Round Robin and the subsequent conclusions leading to the creation of a method for determining GrIS SEC values. The participants used either Envisat radar or ICESat laser altimetry over Jakobshavn Isbræ drainage basin, and the submissions led to inter-comparisons of radar vs. altimetry as well as cross-over vs. repeat-track analyses. Due to the high accuracy of the former and the high spatial resolution of the latter, a method, which combines the two techniques will provide the most accurate SEC estimates. The data supporting the final GrIS analysis stem from the radar altimeters on-board Envisat, ERS-1 and ERS-2. The accuracy of laser data exceeds that of radar altimetry; the Round Robin analysis has, however, proven the latter equally capable of dealing with surface topography thereby making such data applicable in SEC analyses extending all the way from the interior ice sheet to margin regions. This shows good potential for a~future inclusion of ESA CryoSat-2 and Sentinel-3 radar data in the analysis, and thus for obtaining reliable SEC estimates throughout the entire GrIS.

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Interannual variability of elevation on the Greenland ice sheet: effects of firn densification, and establishment of a multi-century benchmark

Journal of Glaciology ◽

10.3189/172756501781832151 ◽

2001 ◽

Vol 47 (158) ◽

pp. 369-377 ◽

Cited By ~ 7

Author(s):

K. M. Cuffey

Keyword(s):

Accumulation Rate ◽

Ice Core ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Surface Elevation ◽

Elevation Change ◽

The Past ◽

Current Climate ◽

Elevation Changes ◽

Past Millennium

AbstractIn order to interpret measurements of ice-sheet surface elevation changes in terms of climatic or dynamic trends, it is necessary to establish the range of stochastic variability of elevation changes resulting from interannual fluctuations of accumulation rate and firn density. The analyses presented here are intended to facilitate such interpretations by defining benchmarks that characterize elevation-change variability in central Greenland, in the current climate and over the past millennium. We use a time- dependent firn-densification model coupled to an ice- and heat-flow model, forced by annual accumulation rate and temperature reconstructions from the Greenland Ice Sheet Project II (GISP2) ice core, to examine the elevation changes resulting from this climatic forcing. From these results, effective firn densities are calculated. These are factors that convert water-equivalent accumulation-rate variability to surface elevation variability. A current-climate benchmark is defined by applying this conversion to Van der Veen and Bolzan’s water-equivalent statistics, and to a 50 year accumulation variability estimate from the GISP2 core. Elevation-change statistics are compiled for the past millennium to define longer-term benchmarks, which show that multi-century variability has been substantially larger than current variability estimated by Van der Veen and Bolzan. It is estimated here that the standard deviation of net elevation change over 5 and 10 year intervals has been 0.27 and 0.38 m, respectively. An approximate method for applying these quantitative results to other dry-snow sites in Greenland is suggested.

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Mapping the aerodynamic roughness of the Greenland ice sheet surface using ICESat-2

10.5194/egusphere-egu21-2136 ◽

2021 ◽

Author(s):

Maurice van Tiggelen ◽

Paul C.J.P. Smeets ◽

Carleen H. Reijmer ◽

Bert Wouters ◽

Jakob F. Steiner ◽

...

Keyword(s):

Eddy Covariance ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Surface Elevation ◽

Spatiotemporal Variability ◽

Atmospheric Models ◽

Laser Altimeter ◽

Eddy Covariance Measurements ◽

Aerodynamic Roughness

The roughness of a natural surface is an important parameter in atmospheric models, as it determines the intensity of turbulent transfer between the atmosphere and the surface. Unfortunately, this parameter is often poorly known, especially in remote areas where neither high-resolution elevation models nor eddy-covariance measurements are available.In this study, we take advantage of the measurements of the ICESat-2 satellite laser altimeter. We use the geolocated photons product (ATL03) to retrieve a 1-m resolution surface elevation product over the K-transect (West Greenland ice sheet). In combination with a bulk drag partitioning model, the retrieved surface elevation is used to estimate the aerodynamic roughness length (z0m) of the surface.We demonstrate the high precision of the retrieved ICESat-2 elevation using co-located UAV photogrammetry, and then evaluate the modelled aerodynamic roughness against multiple in situ eddy-covariance observations. The results point out the importance to use a bulk drag model over a more empirical formulation.The currently available ATL03 geolocated photons are used to map the aerodynamic roughness along the K-transect (2018-2020). We find a considerable spatiotemporal variability in z0m, ranging between 10&#8722;4 m for a smooth snow surface to more than 10&#8722;1 m for rough crevassed areas, which confirms the need to incorporate a variable aerodynamic roughness in atmospheric models over ice sheets.

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Tandem-x Dem Derived Elevation Changes of the Greenland Ice Sheet

IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium ◽

10.1109/igarss.2018.8517404 ◽

2018 ◽

Author(s):

Christian Wohlfart ◽

Birgit Wessel ◽

Martin Huber ◽

Tobias Leichtle ◽

Sahra Abdullahi ◽

...

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Elevation Changes

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25 years of elevation changes of the Greenland Ice Sheet from ERS, Envisat, and CryoSat-2 radar altimetry

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2018.05.015 ◽

2018 ◽

Vol 495 ◽

pp. 234-241 ◽

Cited By ~ 15

Author(s):

Louise Sandberg Sørensen ◽

Sebastian B. Simonsen ◽

René Forsberg ◽

Kirill Khvorostovsky ◽

Rakia Meister ◽

...

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Radar Altimetry ◽

Elevation Changes

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Surface mass balance of the Greenland ice sheet from climate-analysis data and accumulation/runoff models

Annals of Glaciology ◽

10.3189/172756402781816744 ◽

2002 ◽

Vol 35 ◽

pp. 67-72 ◽

Cited By ~ 31

Author(s):

Edward Hanna ◽

Philippe Huybrechts ◽

Thomas L. Mote

Keyword(s):

Mass Balance ◽

Satellite Data ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Snow Accumulation ◽

Surface Elevation ◽

Great Promise ◽

Surface Mass Balance ◽

Ice Dynamics ◽

Surface Mass

AbstractWe used surface climate fields from high-resolution (~0.5660.56˚) European Centre for Medium-RangeWeather Forecasts (ECMWF) operational analyses (1992–98), together with meteorological and glaciological models of snow accumulation and surface meltwater runoff/retention, to produce novel maps of Greenland ice sheet (GIS) net accumulation, net runoff and surface mass balance (SMB). We compared our runoff maps with similar-scaled runoff (melt minus refreezing) maps based on passive-microwave satellite data. Our gross spatial/temporal patterns of runoff compared well with those from the satellite data, although amounts of modelled runoff are likely too low. Mean accumulation was 0.287 (0.307)ma–1, and mean runoff was 0.128 (0.151)ma–1, averaged across the W. Abdalati (T. L. Mote) GIS mask. Corresponding mean SMB was 0.159 (0.156)ma–1, with considerable interannual variability (standard deviation ~0.11ma–1) primarily due to variations in runoff. Considering best estimates of current iceberg calving, overall the GIS is probably currently losing mass. Our study shows great promise for meaningfully modelling SMB based on forthcoming ``second-generation’’ ECMWF re-analysis (ERA-40) data, and comparing the results with ongoing laser/radarmeasurements of surface elevation. This should help elucidate to what extent surface elevation changes are caused by short-term SMB variations or other factors (e.g. ice dynamics).

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The importance of slope correction for studying Greenland ice change using radar altimetry (CryoSat-2)

10.5194/egusphere-egu2020-15264 ◽

2020 ◽

Author(s):

Katarzyna Sejan ◽

Bert Wouters ◽

Michiel van den Broeke

Keyword(s):

Slope Angle ◽

Greenland Ice Sheet ◽

Correction Method ◽

Surface Elevation ◽

Laser Altimetry ◽

Radar Altimetry ◽

Slope Correction ◽

Long Time ◽

Elevation Changes ◽

Satellite Radar

Satellite radar altimetry is one of the most important tools for monitoring changes in the mass balance of the world's ice sheets. Acquiring long time series of elevation changes is crucial, and the long lifetime of the CryoSat-2 mission has contributed wonderfully to this effort. However, once the CryoSat-2 mission ends, it will be important to bridge the gap between CryoSat-2 and future radar altimetry missions. IceSat2 data can help aid this effort, assuming that the appropriate processing techniques are used to allow the comparison of radar and laser altimetry. Furthermore, different altimetry techniques come with their own pitfalls, in radar altimetry signal penetration into the snowpack introduces ambiguity in the origin of reflected echo, a major issue not present in laser altimetry. It is therefore important to minimize this ambiguity by developing processing algorithms for the radar altimetry form CryoSat-2 mission, with a special attention on relating it to the IceSat2 mission. &#160;Focusing on Greenland Ice Sheet (GIS), we have developed a processing chain for the estimation of surface elevations and elevation changes from the ESA level-1 product (L1b) Baseline D. As a first step, we investigated the importance of Digital Elevation Model (DEM) in the slope correction algorithm and how it affects the estimated surface elevation.&#160;The waveform retracker algorithm was developed following the method by Nilsson (2015) with a range of thresholds in the threshold retracker applied to the waveform. Knowing the estimated range and the altitude of the satellite at the time of the measurement, we calculated the corresponding surface elevation at the point of the wavelet reflection.We apply a slope correction method by Hurkmans (2012), where displacement from the nadir location in x- and y- directions is calculated using the slope angle and aspect retrieved from a DEM, giving a new set of coordinates that represents the location of the estimated elevation. We use two sets of slope angle and aspect calculated from two DEMs, ArcticDEM Release 7 (Porter et al., 2018) and Greenland Ice Mapping Project (GIMP) DEM (Howat et al., 2017). Both DEMs are similar in terms of optical imagery data source, processing and resolution, however, they have been referenced to different laser altimetry data. We investigate this effect in the slope correction of radar altimetry from CryoSat2 mission.We checked the two sets of slope correction data using IceSat-2 data (Smith et al., 2019) corresponding to the same time period, and selected by nearest point calculation. We analyze and discuss the differences between IceSat-2 data and CryoSat-2 data with slope correction using GIMP DEM or ArcticDEM.

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Detecting active subglacial lakes beneath the Greenland Ice Sheet using ArcticDEM

10.5194/egusphere-egu2020-9431 ◽

2020 ◽

Author(s):

Jade Bowling ◽

Amber Leeson ◽

Malcolm McMillan ◽

Stephen Livingstone ◽

Andrew Sole

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Surface Elevation ◽

Surface Model ◽

Ice Dynamics ◽

Subglacial Lake ◽

Flow Speeds ◽

Elevation Data ◽

Hydrological System ◽

Subglacial Lakes

A total of 63 subglacial lakes have been documented beneath the Greenland Ice Sheet using a combination of radio-echo sounding and surface elevation change measurements. Of these, only 7 lakes have shown evidence of hydrological activity over the period 2001-2018. Draining lakes have been observed to drive transient changes in local ice flow speeds in Antarctica. The sudden discharge of water during a subglacial lake outburst event causes the subglacial lake roof to subside, which propagates to the surface, resulting in the formation of collapse basins (typically ~50-70 m in depth). These surface features can be detected using remote sensing techniques.Whilst over 100 active subglacial lakes have been identified in Antarctica, predominantly beneath ice streams, little is known about the extent, volume of water stored and residence times of active subglacial lakes in Greenland, together with any potential influence of drainage events on local ice dynamics and sediment evacuation rates. Here, we explore the potential of the high resolution ArcticDEM stereogrammetric digital surface model (DSM) open source dataset, generated from satellite optical imagery, to identify and monitor subglacial lake-derived collapse basins. The ArcticDEM provides 2 m time-stamped surface elevation data, covering ~160 million km2, offering an exciting opportunity to map elevation changes between 2009-2017. This study presents the first effort to utilise ArcticDEM data at an ice-sheet scale to identify and monitor active subglacial lakes beneath the Greenland Ice Sheet, which we hope will ultimately improve our understanding of its complex subglacial hydrological system.

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FUSION OF LASER ALTIMETRY DATA WITH DEMS DERIVED FROM STEREO IMAGING SYSTEMS

ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences ◽

10.5194/isprsarchives-xli-b8-531-2016 ◽

2016 ◽

Vol XLI-B8 ◽

pp. 531-536

Author(s):

T. Schenk ◽

B. M. Csatho ◽

K. Duncan

Keyword(s):

Time Series ◽

Ice Sheet ◽

Surface Shape ◽

Imaging Systems ◽

Surface Elevation ◽

Altimetry Data ◽

Laser Altimetry ◽

Point Distribution ◽

Spatial Coverage ◽

Elevation Changes

During the last two decades surface elevation data have been gathered over the Greenland Ice Sheet (GrIS) from a variety of different sensors including spaceborne and airborne laser altimetry, such as NASA’s Ice Cloud and land Elevation Satellite (ICESat), Airborne Topographic Mapper (ATM) and Laser Vegetation Imaging Sensor (LVIS), as well as from stereo satellite imaging systems, most notably from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Worldview. The spatio-temporal resolution, the accuracy, and the spatial coverage of all these data differ widely. For example, laser altimetry systems are much more accurate than DEMs derived by correlation from imaging systems. On the other hand, DEMs usually have a superior spatial resolution and extended spatial coverage. We present in this paper an overview of the SERAC (Surface Elevation Reconstruction And Change detection) system, designed to cope with the data complexity and the computation of elevation change histories. SERAC simultaneously determines the ice sheet surface shape and the time-series of elevation changes for surface patches whose size depends on the ruggedness of the surface and the point distribution of the sensors involved. By incorporating different sensors, SERAC is a true fusion system that generates the best plausible result (time series of elevation changes) a result that is better than the sum of its individual parts. We follow this up with an example of the Helmheim gacier, involving ICESat, ATM and LVIS laser altimetry data, together with ASTER DEMs.

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