ESA ice sheet CCI: derivation of the optimal method for surface elevation change detection of the Greenland ice sheet – round robin results

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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Surface elevation change of the Greenland ice sheet from an analysis of Seasat and Geosat altimeter data

Proceedings of IGARSS '94 - 1994 IEEE International Geoscience and Remote Sensing Symposium ◽

10.1109/igarss.1994.399748 ◽

2002 ◽

Author(s):

C.H. Davis

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Surface Elevation ◽

Altimeter Data ◽

Elevation Change ◽

Surface Elevation Change

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ICE SHEET ELEVATION MAPPING AND CHANGE DETECTION WITH THE ICE, CLOUD AND LAND ELEVATION SATELLITE-2

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

10.5194/isprs-archives-xlii-2-w13-1747-2019 ◽

2019 ◽

Vol XLII-2/W13 ◽

pp. 1747-1751 ◽

Cited By ~ 1

Author(s):

B. M. Csatho ◽

A. F. Schenk ◽

T. Neumann

Keyword(s):

Time Series ◽

Change Detection ◽

Ice Sheet ◽

Simulated Data ◽

Surface Elevation ◽

Elevation Change ◽

Laser Altimetry ◽

Calibration And Validation ◽

Ice Cloud ◽

Surface Elevation Change

<p><strong>Abstract.</strong> On September 15, 2018, ICESat-2 (Ice, Cloud, and land Elevation satellite) was successfully launched to measure ice sheet and glacier elevation change, sea ice freeboard, and vegetation. This paper describes the computation of surface elevation change rates obtained with SERAC (Surface Elevation Reconstruction And Change detection) from ICESat-2 observations. After summarizing some relevant aspects of ICESat-2 and its sole instrument ATLAS (Advanced Topographic Laser Altimetry System) the paper focuses on how we calculate time series of elevation change rates from ICESat-2’s data product ATL03. Since real ICESat-2 data suitable for generating time series of several time epochs are not yet available, we used simulated data for this study. We will start generating time series from real ICESat-2 data after the conclusion of the ongoing calibration and validation phase and we expect to present real-world examples at the WG III/9 meeting in June, 2019 in Enschede, The Netherlands.</p>

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Elevation change of the Greenland Ice Sheet due to surface mass balance and firn processes, 1960–2014

The Cryosphere ◽

10.5194/tc-9-2009-2015 ◽

2015 ◽

Vol 9 (6) ◽

pp. 2009-2025 ◽

Cited By ~ 36

Author(s):

P. Kuipers Munneke ◽

S. R. M. Ligtenberg ◽

B. P. Y. Noël ◽

I. M. Howat ◽

J. E. Box ◽

...

Keyword(s):

Mass Balance ◽

Volume Change ◽

Climate Model ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Surface Elevation ◽

Surface Mass Balance ◽

Elevation Change ◽

Ice Dynamics ◽

Surface Mass

Abstract. Observed changes in the surface elevation of the Greenland Ice Sheet are caused by ice dynamics, basal elevation change, basal melt, surface mass balance (SMB) variability, and by compaction of the overlying firn. The last two contributions are quantified here using a firn model that includes compaction, meltwater percolation, and refreezing. The model is forced with surface mass fluxes and temperature from a regional climate model for the period 1960–2014. The model results agree with observations of surface density, density profiles from 62 firn cores, and altimetric observations from regions where ice-dynamical surface height changes are likely small. In areas with strong surface melt, the firn model overestimates density. We find that the firn layer in the high interior is generally thickening slowly (1–5 cm yr−1). In the percolation and ablation areas, firn and SMB processes account for a surface elevation lowering of up to 20–50 cm yr−1. Most of this firn-induced marginal thinning is caused by an increase in melt since the mid-1990s and partly compensated by an increase in the accumulation of fresh snow around most of the ice sheet. The total firn and ice volume change between 1980 and 2014 is estimated at −3295 ± 1030 km3 due to firn and SMB changes, corresponding to an ice-sheet average thinning of 1.96 ± 0.61 m. Most of this volume decrease occurred after 1995. The computed changes in surface elevation can be used to partition altimetrically observed volume change into surface mass balance and ice-dynamically related mass changes.

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Four decades of surface elevation change of the Antarctic Ice Sheet from multi-mission satellite altimetry

10.5194/tc-2018-49 ◽

2018 ◽

Cited By ~ 1

Author(s):

Ludwig Schröder ◽

Martin Horwath ◽

Reinhard Dietrich ◽

Veit Helm

Keyword(s):

Time Series ◽

Satellite Altimetry ◽

Ice Sheet ◽

Surface Elevation ◽

Elevation Change ◽

Antarctic Ice Sheet ◽

Mission Satellite ◽

Surface Elevation Change ◽

Precipitation Anomalies ◽

The Antarctic

Abstract. We developed an approach for a multi-mission satellite altimetry analysis over the Antarctic Ice Sheet which comprises Seasat, Geosat, ERS-1, ERS-2, Envisat, ICESat and CryoSat-2. In a first step we apply a consistent reprocessing of the radar alitmetry data which improves the measurement precision by up to 50 %. We then perform a joint repeat altimetry analysis of all missions. We estimate inter-mission offsets by approaches adapted to the temporal overlap or non-overlap and to the similarity or dissimilarity of involved altimetry techniques. Hence, we obtain monthly grids forming a combined surface elevation change time series. Owing to the early missions Seasat and Geosat, the time series span almost four decades from 07/1978 to 12/2017 over 25 % of the ice sheet area (coastal regions of East Antarctica and the Antarctic Peninsula). Since the launch of ERS-1 79 % of the ice sheet area is covered by observations. Over this area, we obtain a negative volume trend of −34 ± 5 km3 yr−1 for the more than 25-year period (04/1992–12/2017). These volume losses have significantly accelerated to a rate of −170 ± 11 km3 yr−1 for 2010–2017. Interannual variations significantly impact decadal volume rates which highlights the importance of the long-term time series. Our time series show a high coincidence with modeled cumulated precipitation anomalies and with satellite gravimetry. This supports the interpretation with respect to snowfall anomalies or dynamic thinning. Moreover, the correlation with cumulated precipitation anomalies back to the Seasat and Geosat periods highlights that the inter-mission offsets were successfully corrected and that the early missions add valuable information.

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The effect of anisotropic flow properties on ice-sheet surface elevation change

Annals of Glaciology ◽

10.3189/172756404781813989 ◽

2004 ◽

Vol 39 ◽

pp. 439-444 ◽

Cited By ~ 1

Author(s):

Weili Wang ◽

Jun Li ◽

Jay Zwally ◽

Vin Morgan ◽

Tas D. Van Ommen

Keyword(s):

Strain Rate ◽

Ice Sheet ◽

Surface Elevation ◽

Ice Thickness ◽

Flow Properties ◽

Elevation Change ◽

Ice Flow ◽

Anisotropic Flow ◽

Sheet Surface ◽

Surface Elevation Change

AbstractAn ice-flow model has been developed and applied to Law Dome, East Antarctica, at the location of the Dome Summit South deep borehole. The results are used to reconstruct an ice-sheet history of accumulation rate, ice thickness and the rate of change in ice thickness. The focus of this study is on the effect of the variation in anisotropic flow properties on the ice-sheet surface elevation change. The enhancement factor, defined as the ratio of the strain rate for anisotropic ice to the strain rate for isotropic ice, is used in the ice-flow relations to account for the anisotropic properties of the ice with fabric development. The model is run with the various ice rheologies which represent anisotropic or isotropic ice-flow properties. The results show that the model incorporating anisotropic flow properties of the ice is more sensitive to the climate-change history.

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Satellite Remote Sensing of the Greenland Ice Sheet Ablation Zone: A Review

Remote Sensing ◽

10.3390/rs11202405 ◽

2019 ◽

Vol 11 (20) ◽

pp. 2405

Author(s):

Matthew Cooper ◽

Laurence Smith

Keyword(s):

Remote Sensing ◽

Mass Balance ◽

Satellite Remote Sensing ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Ablation Zone ◽

Elevation Change ◽

Laser Altimetry ◽

Surface Elevation Change ◽

Optical Imagery

The Greenland Ice Sheet is now the largest land ice contributor to global sea level rise, largely driven by increased surface meltwater runoff from the ablation zone, i.e., areas of the ice sheet where annual mass losses exceed gains. This small but critically important area of the ice sheet has expanded in size by ~50% since the early 1960s, and satellite remote sensing is a powerful tool for monitoring the physical processes that influence its surface mass balance. This review synthesizes key remote sensing methods and scientific findings from satellite remote sensing of the Greenland Ice Sheet ablation zone, covering progress in (1) radar altimetry, (2) laser (lidar) altimetry, (3) gravimetry, (4) multispectral optical imagery, and (5) microwave and thermal imagery. Physical characteristics and quantities examined include surface elevation change, gravimetric mass balance, reflectance, albedo, and mapping of surface melt extent and glaciological facies and zones. The review concludes that future progress will benefit most from methods that combine multi-sensor, multi-wavelength, and cross-platform datasets designed to discriminate the widely varying surface processes in the ablation zone. Specific examples include fusing laser altimetry, radar altimetry, and optical stereophotogrammetry to enhance spatial measurement density, cross-validate surface elevation change, and diagnose radar elevation bias; employing dual-frequency radar, microwave scatterometry, or combining radar and laser altimetry to map seasonal snow depth; fusing optical imagery, radar imagery, and microwave scatterometry to discriminate between snow, liquid water, refrozen meltwater, and bare ice near the equilibrium line altitude; combining optical reflectance with laser altimetry to map supraglacial lake, stream, and crevasse bathymetry; and monitoring the inland migration of snowlines, surface melt extent, and supraglacial hydrologic features.

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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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Re-evaluation of paleo-accumulation parameterization over Northern Hemisphere ice sheets during the ice age examined with a high-resolution AGCM and a 3-D ice-sheet model

Annals of Glaciology ◽

10.3189/172756405781813032 ◽

2005 ◽

Vol 42 ◽

pp. 433-440 ◽

Cited By ~ 9

Author(s):

Takateru Yamagishi ◽

Ayako Abe-Ouchi ◽

Fuyuki Saito ◽

Tomonori Segawa ◽

Teruyuki Nishimura

Keyword(s):

High Resolution ◽

Northern Hemisphere ◽

General Circulation ◽

Ice Sheet ◽

Precipitation Change ◽

Ice Age ◽

Surface Elevation ◽

Laurentide Ice Sheet ◽

Elevation Change ◽

Surface Elevation Change

AbstractSimulations of the Northern Hemisphere ice sheet at the Last Glacial Maximum (LGM; 21 kyr BP) are performed using a high-resolution atmospheric general circulation model (AGCM) in order to re-evaluate the conventional surface temperature- or elevation-based parameterization. The influence of precipitation change on the steady-state topography of the Laurentide ice sheet at the LGM is estimated using an AGCM with a horizontal resolution of ∼1° and a three-dimensional thermomechanically coupled ice-sheet model. The ice volume estimated by the AGCM simulation is much larger than that indicated by the conventional parameterization. Through sensitivity analysis of the AGCM and ice-sheet model, it is found that the rate of precipitation change depends on the location of the ice sheet, and that the rate of precipitation change due to surface elevation change is higher than the rate unrelated to surface elevation change on the Laurentide ice sheet. The rate of precipitation is also shown to exhibit seasonality and regionality due to effects such as interior desertification and the concentration of storm tracks.

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