Unusual surface morphology from digital elevation models of the Greenland Ice Sheet

Digital Elevation Models (DEMs) of Greenland provide the basic data for studying the Greenland ice sheet (GrIS), but little research quantitatively evaluates and compares the accuracy of various Greenland DEMs. This study uses IceBridge elevation data to evaluate the accuracies of the the Greenland Ice Map Project (GIMP)1 DEM, GIMP2 DEM, TanDEM-X, and ArcticDEM in their corresponding time ranges. This study also analyzes the impact of DEM accuracy and resolution on the accuracy of river network extraction. The results show that (1) within the time range covered by each DEM, TanDEM-X with an RMSE of 5.60 m has higher accuracy than the other DEMs in terms of absolute height accuracy, while GIMP1 has the lowest accuracy among the four Greenland DEMs, with an RMSE of 14.34 m. (2) Greenland DEMs are affected by regional errors and interannual changes. The accuracy in areas with elevations above 2000 m is higher than that in areas with elevations below 2000 m, and better accuracy is observed in the north than in the south. The stability of the ArcticDEM product is higher than those of the other three DEM products, and its RMSE standard deviation over multiple years is only 0.14 m. Therefore, the errors caused by the applications of DEMs with longer time spans are smaller. GIMP1 performs in an opposite manner, with a standard deviation of 2.39 m. (3) The river network extracted from TanDEM-X is close to the real river network digitized from remote sensing images, with an accuracy of 50.78%. The river network extracted from GIMP1 exhibits the largest errors, with an accuracy of only 8.83%. This study calculates and compares the accuracy of four Greenland DEMs and indicates that TanDEM-X has the highest accuracy, adding quantitative studies on the accuracy evaluation of various Greenland DEMs. This study also compares the results of different DEM river network extractions, verifies the impact of DEM accuracy on the accuracy of the river network extraction results, and provides an explorable direction for the hydrological analysis of Greenland as a whole.

Download Full-text

On the influence of Greenland outlet glacier bed topography on results from dynamic ice-sheet models

Annals of Glaciology ◽

10.3189/2012aog60a061 ◽

2012 ◽

Vol 53 (60) ◽

pp. 281-293 ◽

Cited By ~ 12

Author(s):

Ute C. Herzfeld ◽

James Fastook ◽

Ralf Greve ◽

Brian McDonald ◽

Bruce F. Wallin ◽

...

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Surface Velocity ◽

Ice Dynamics ◽

Outlet Glacier ◽

Digital Elevation ◽

Ice Sheet Modeling ◽

Subglacial Topography

AbstractPrediction of future changes in dynamics of the Earth’s ice sheets, mass loss and resultant contribution to sea-level rise are the main objectives of ice-sheet modeling. Mass transfer from ice sheet to ocean is, in large part, through outlet glaciers. Subglacial topography plays an important role in ice dynamics; however, trough systems have not been included in bed digital elevation models (DEMS) used in modeling, because their size is close to the model resolution. Using recently collected CReSIS MCoRDs data of subglacial topography and an algorithm that allows topographically and morphologically correct integration of troughs and trough systems at any modeling scale (5 km resolution for SeaRISE), an improved Greenland bed DEM was developed that includes Jakobshavn Isbræ, Helheim, Kangerdlussuaq and Petermann glaciers (JakHelKanPet DEM). Contrasting the different responses of two Greenland ice-sheet models (UMISM and SICOPOLIS) to the more accurately represented bed shows significant differences in modeled surface velocity, basal water production and ice thickness. Consequently, modeled ice volumes for the Greenland ice sheet are significantly smaller using the JakHelKanPet DEM, and volume losses larger. More generally, the study demonstrates the role of spatial modeling of data specifically as input for dynamic ice-sheet models in assessments of future sea-level rise.

Download Full-text

Cascading water underneath Wilkes Land, East Antarctic ice sheet, observed using altimetry and digital elevation models

The Cryosphere ◽

10.5194/tc-8-673-2014 ◽

2014 ◽

Vol 8 (2) ◽

pp. 673-687 ◽

Cited By ~ 18

Author(s):

T. Flament ◽

E. Berthier ◽

F. Rémy

Keyword(s):

Digital Elevation Models ◽

Ice Sheet ◽

Data Set ◽

Antarctic Ice Sheet ◽

Digital Elevation ◽

Wilkes Land ◽

Stereo Imagery ◽

Lake Drainage ◽

Subglacial Lakes ◽

East Antarctic Ice Sheet

Abstract. We describe a major subglacial lake drainage close to the ice divide in Wilkes Land, East Antarctica, and the subsequent cascading of water underneath the ice sheet toward the coast. To analyse the event, we combined altimetry data from several sources and subglacial topography. We estimated the total volume of water that drained from Lake CookE2 by differencing digital elevation models (DEM) derived from ASTER and SPOT5 stereo imagery acquired in January 2006 and February 2012. At 5.2 ± 1.5 km3, this is the largest single subglacial drainage event reported so far in Antarctica. Elevation differences between ICESat laser altimetry spanning 2003–2009 and the SPOT5 DEM indicate that the discharge started in November 2006 and lasted approximately 2 years. A 13 m uplift of the surface, corresponding to a refilling of about 0.6 ± 0.3 km3, was observed between the end of the discharge in October 2008 and February 2012. Using the 35-day temporal resolution of Envisat radar altimetry, we monitored the subsequent filling and drainage of connected subglacial lakes located downstream of CookE2. The total volume of water traveling within the theoretical 500-km-long flow paths computed with the BEDMAP2 data set is similar to the volume that drained from Lake CookE2, and our observations suggest that most of the water released from Lake CookE2 did not reach the coast but remained trapped underneath the ice sheet. Our study illustrates how combining multiple remote sensing techniques allows monitoring of the timing and magnitude of subglacial water flow beneath the East Antarctic ice sheet.

Download Full-text

An image-enhanced DEM of the Greenland ice sheet

Annals of Glaciology ◽

10.3189/172756402781817969 ◽

2002 ◽

Vol 34 ◽

pp. 291-298 ◽

Cited By ~ 42

Author(s):

Ted A. Scambos ◽

Terry Haran

Keyword(s):

Accumulation Rate ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Airborne Laser ◽

Relief Surface ◽

Digital Elevation ◽

Lateral Extent ◽

The Mean ◽

Elevation Model ◽

Very High

AbstractWe have assembled an elevation grid for the Greenland ice sheet using a combination of the best current digital elevation model (DEM) (Bamber and others, 2000a, 2001) and 44 Advanced Very High Resolution Radiometer satellite images acquired in spring 1997. The images are used to quantitatively enhance the representation of surface undulations through photoclinometry. Gridcell spacing of the new DEM is 625 m. To validate the new DEM, we compared profiles extracted from it and the Bamber and others DEM with airborne laser altimetry profiles collected in the 1990s by the Airborne Topographic Mapper (Krabill and others, 1995). The image-enhanced DEM has a greatly improved representation of decameter-relief surface features <15 km in lateral extent, and reduces the mean elevation error in regions having these features by 20–50%. Root-mean-squared errors are typically 7–15m in the Bamber DEM, and 4–10m after image enhancement. However, the photoclinometry process adds some noise. In very smooth portions of the ice sheet where decameter undulationsare absent, the photoclinometry process caused a slight increase in the rms error, from ~1 min the Bamber and others DEM to ∼2.5 min the image-enhanced DEM. The image-enhanced DEM will be useful for inferring accumulation-rate variations over the undulation field, or for improving maps of bedrock elevation through inversion of surface elevation, for example. We briefly explore the preliminary steps of this latter application.

Download Full-text

The Greenland Ice Mapping Project (GIMP) land classification and surface elevation datasets

The Cryosphere Discussions ◽

10.5194/tcd-8-453-2014 ◽

2014 ◽

Vol 8 (1) ◽

pp. 453-478 ◽

Cited By ~ 28

Author(s):

I. M. Howat ◽

A. Negrete ◽

B. E. Smith

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Image Mosaic ◽

Terrain Classification ◽

Land Classification ◽

Registration Error ◽

Digital Elevation ◽

Landsat 7 ◽

Elevation Model ◽

Ice Sheet Mapping

Abstract. As part of the Greenland Ice-sheet Mapping Project (GIMP) we have produced three geospatial datasets for the entire ice sheet and periphery. These are (1) a complete, 15 m resolution image mosaic, (2) ice-covered and ice-free terrain classification masks, also posted to 15 m resolution and (3) a complete, altimeter-registered Digital Elevation Model posted at 30 m. The image mosaic was created from a combination of Landsat-7 and RADARSAT-1 imagery acquired between 1999 and 2002. Each pixel in the image is stamped with the acquisition date and geo-registration error to facilitate change detection. This mosaic was then used to manually produce complete ice-covered and ice-free land classification masks. Finally, we used satellite altimetry and stereo-photogrammetric DEMs to enhance an existing DEM for Greenland, substantially improving resolution and accuracy over the ice margin and periphery.

Download Full-text

Controls on the basal water pressure in subglacial channels near the margin of the Greenland ice sheet

Journal of Glaciology ◽

10.3189/172756505781829214 ◽

2005 ◽

Vol 51 (174) ◽

pp. 443-450 ◽

Cited By ~ 12

Author(s):

Andreas P. Ahlstrøm ◽

Johan J. Mohr ◽

Niels Reeh ◽

Erik Lintz Christensen ◽

Roger LeB. Hooke

Keyword(s):

Water Pressure ◽

Ice Sheet ◽

Drainage System ◽

Greenland Ice Sheet ◽

Interferometric Synthetic Aperture Radar ◽

Satellite Repeat ◽

Digital Elevation ◽

Catchment Size ◽

Subglacial Topography ◽

Enhanced Surface

AbstractAssuming a channelized drainage system in steady state, we investigate the influence of enhanced surface melting on the water pressure in subglacial channels, compared to that of changes in conduit geometry, ice rheology and catchment variations. The analysis is carried out for a specific part of the western Greenland ice-sheet margin between 66° N and 66°30′N using new high-resolution digital elevation models of the subglacial topography and the ice-sheet surface, based on an airborne ice-penetrating radar survey in 2003 and satellite repeat-track interferometric synthetic aperture radar analysis of European Remote-sensing Satellite 1 and 2 (ERS-1/-2) imagery, respectively. The water pressure is calculated up-glacier along a likely subglacial channel at distances of 1, 5 and 9 km from the outlet at the ice margin, using a modified version of Röthlisberger’s equation. Our results show that for the margin of the western Greenland ice sheet, the water pressure in subglacial channels is not sensitive to realistic variations in catchment size and mean surface water input compared to small changes in conduit geometry and ice rheology.

Download Full-text

Cascading water underneath Wilkes Land, East Antarctic Ice Sheet, observed using altimetry and digital elevation models

The Cryosphere Discussions ◽

10.5194/tcd-7-841-2013 ◽

2013 ◽

Vol 7 (2) ◽

pp. 841-871 ◽

Cited By ~ 3

Author(s):

T. Flament ◽

E. Berthier ◽

F. Rémy

Keyword(s):

Digital Elevation Models ◽

Ice Sheet ◽

Data Set ◽

Antarctic Ice Sheet ◽

Digital Elevation ◽

Wilkes Land ◽

Stereo Imagery ◽

Lake Drainage ◽

Subglacial Lakes ◽

East Antarctic Ice Sheet

Abstract. We describe a major subglacial lake drainage close to the ice divide in Wilkes Land, East Antarctica, and the subsequent cascading of water underneath the ice sheet toward the coast. To analyze the event, we combined altimetry data from several sources and bedrock data. We estimated the total volume of water that drained from Lake CookE2 by differencing digital elevation models (DEM) derived from ASTER and SPOT5 stereo-imagery. With 5.2 ± 0.5 km3, this is the largest single subglacial drainage event reported so far in Antarctica. Elevation differences between ICESat laser altimetry and the SPOT5 DEM indicate that the discharge lasted approximately 2 yr. A 13-m uplift of the surface, corresponding to a refilling of about 0.64 ± 0.32 km3, was observed between the end of the discharge in October 2008 and February 2012. Using Envisat radar altimetry, with its high 35-day temporal resolution, we monitored the subsequent filling and drainage of connected subglacial lakes located downstream. In particular, a transient temporal signal can be detected within the theoretical 500-km long flow paths computed with the BEDMAP2 data set. The volume of water traveling in this wave is in agreement with the volume that drained from Lake CookE2. These observations contribute to a better understanding of the water transport beneath the East Antarctic ice sheet.

Download Full-text

Assessment of a TanDEM-X Digital Elevation Model of the Greenland Ice Sheet and its Zonation for Winter 2015/16

10.5194/egusphere-egu2020-6739 ◽

2020 ◽

Author(s):

Sabine Baumann ◽

Birgit Wessel ◽

Martin Huber ◽

Silke Kerkhoff ◽

Achim Roth

Keyword(s):

Remote Sensing ◽

Digital Elevation Model ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Polar Regions ◽

Digital Elevation ◽

And Performance ◽

Remote Sensing Symposium ◽

Global Sea Level ◽

Elevation Model

The Greenland Ice Sheet (GIS) was the largest contributor to global sea level rise in the 2005 to 2016 period (Meredith et al. in press). Therefore, it is one of the biggest players influencing our climate and monitoring and understanding of its mechanisms and development are of highest relevance.Means to observe and measure such large areas are remote sensing. The Tandem-X mission of DLR and Airbus consists of two satellites (TerraSAR-X and TanDEM-X) that are flying in single pass formation, mapping the Earth in interferometric SAR X-band with a resolution of 12m (Zink et al. 2014). The mission has been flying in this constellation since 2010. Due to the satellite constellation and the SAR system, digital elevation models (DEMs) can be created in high resolution, unaffected by the availability of daylight and the presence of clouds.All data acquired between 2010 to 2014 (Rizzoli et al. 2017) were compled to a global elevation model. Besides this global product, several time slices were created for the GIS (Wohlfart et al. 2018). In this project, we created a DSM mosaic from winter 2015/16 acquisitions, more precisely using more than 2000 DEM scenes (Fritz at al. 2011) from end of October 2015 to beginning of February 2016.One issue of a SAR system is the penetration of the signal into snow. Additionally, water surfaces appear dark in the images due to low backscatter towards the sensor. Therefore, we used winter scenes to minimize the height error.We created an almost seamless DSM out of these scenes for 2015/16. Second, we used SAR features to delineate different snow zones. For this purpose, we used the amplitude, the height error map, and additionally ICESat and ICE Bridge data.&#160;References Fritz, T.; Rossi, C.; Yague-Martinez, N.; Rodriguez Gonzalez, F.; Lachaise, M.; Breit H. Interferometric processing of TanDEM-X data, IGARSS 2011, Vancouver, July 2011Meredith, M.; Sommerkorn M.; Cassotta S.; Derksen C.; Ekaykin A.; Hollowed A.; Kofinas G.; Mackintosh A.; Melbourne-Thomas J.; Muelbert M.M.C.; Ottersen G.; Pritchard H.; and Schuur E.A.G.; 2019: Polar Regions. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.-O. Po&#776;rtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegri&#769;a, M. Nicolai, A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.)]. In press.Rizzoli, P.; Martone, M.; Gonzalez, C.; Wecklich, C.; Tridon, D.B.; Br&#228;utigam, B.; Bachmann, M.; Schulze, D.; Fritz, T.; Huber, M.; et al. Generation and performance assessment of the global TanDEM-X digital elevation model. ISPRS J. Photogramm. Remote Sens. 2017, 132, 119&#8211;139.Wohlfart, C.; Wessel, B.; Huber, M.; Leichtle, T.; Abdullahi, S.; Kerkhoff, S.; Roth, A. TanDEM-X DEM derived elevation changes of the Greenland Ice Sheet. In Proceedings of the IEEE International Geoscience and Remote Sensing Symposium (IGARSS), Valencia, Spain, 22&#8211;27 July 2018.Zink, M.; Bachmann, M.; Br&#228;utigam, B.; Fritz, T.; Hajnsek, I.; Krieger, G.; Moreira, A.; Wessel, B. TanDEM-X: The New Global DEM Takes Shape. IEEE GRSM 2014, 2, 8&#8211;23.

Download Full-text

A comparison of balance velocities, measured velocities and thermomechanically modelled velocities for the Greenland ice sheet

Annals of Glaciology ◽

10.3189/172756400781820589 ◽

2000 ◽

Vol 30 ◽

pp. 211-216 ◽

Cited By ~ 10

Author(s):

J. L. Bamber ◽

R. J. Hardy ◽

P. Huybrechts ◽

Ian Joughin

Keyword(s):

Global Positioning System ◽

General Pattern ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Good Representation ◽

Synthetic Aperture Radar Interferometry ◽

Digital Elevation ◽

Global Positioning ◽

System Data ◽

Elevation Model

AbstractBalance velocities for the Greenland ice sheet have been calculated from a new digital-elevation model, accumulation-rates compilation and an existing ice-thickness grid, using a two-dimensional finite-difference scheme. The pattern of velocities over the ice sheet is presented and compared with velocities derived from synthetic-aperture-radar interferometry for part of northern Greenland and a limited number of global positioning system data. This comparison indicated that the balance-velocity scheme and boundary conditions used here provide a remarkably good representation of the dynamics of the ice sheet inland from the margins. It is suggested, therefore, that these balance-velocity data could provide a valuable method of constraining a numerical ice-sheet model. The balance velocities were compared with the diagnostic velocity field calculated from several different configurations of a numerical ice-sheet model. The general pattern of flow agrees well. The detail, however, is quite different. For example, the large (>300km) ice stream in the northeast is not generated by the numerical model and much of the detailed flow pattern is completely lost due to the limited model resolution and limitations in the model physics.

Download Full-text