scholarly journals Thickening of Jakobshavns Isbræ, West Greenland, measured by airborne laser altimetry

1995 ◽  
Vol 21 ◽  
pp. 259-262 ◽  
Author(s):  
R. Thomas ◽  
W. Rkabill ◽  
E. Frederick ◽  
K. Jezek
Keyword(s):  
Ice Sheet ◽  
Drainage Basins ◽  
Laser Altimeter ◽  
Additional Increase ◽  
Gps Navigation ◽  
Ice Surface ◽  
Airborne Laser ◽  
Global Positioning ◽  
Long Term Trends

NASA flights over southern Greenland in 1991, 1992 and 1993, using a scanning laser altimeter with Global Positioning System (GPS) navigation, have demonstrated a capability to measure ice-surface elevations to an accuracy of 10-15 cm. Flights over Jakobshavns Isbræ revealed winter thickening by several meters between September 1991 and April 1992. By July 1993, surface elevations showed a small additional increase, possibly associated with the cold 1992 summer. Data collected over the ice sheet east of Jakobshavns Isbræ show negligible change over the same period; but further south, at latitude 65 N, the western part of the ice sheet appears to have thickened by up to 2 m between 1980 and 1993. It is clear that such measurements must be continued over many years, both to quantify the effects of inter-annual variability and to measure long-term trends. To this end, we plan to complete a first survey of all major drainage basins on the ice sheet in May-June 1994, and then to resurvey all flight lines at 5a intervals, with more frequent flights over selected routes.

scholarly journals Thickening of Jakobshavns Isbræ, West Greenland, measured by airborne laser altimetry

1995 ◽  
Vol 21 ◽  
pp. 259-262 ◽  
Author(s):  
R. Thomas ◽  
W. Rkabill ◽  
E. Frederick ◽  
K. Jezek
Keyword(s):  
Ice Sheet ◽  
Drainage Basins ◽  
Laser Altimeter ◽  
Additional Increase ◽  
Gps Navigation ◽  
Ice Surface ◽  
Airborne Laser ◽  
Global Positioning ◽  
Long Term Trends

NASA flights over southern Greenland in 1991, 1992 and 1993, using a scanning laser altimeter with Global Positioning System (GPS) navigation, have demonstrated a capability to measure ice-surface elevations to an accuracy of 10-15 cm. Flights over Jakobshavns Isbræ revealed winter thickening by several meters between September 1991 and April 1992. By July 1993, surface elevations showed a small additional increase, possibly associated with the cold 1992 summer. Data collected over the ice sheet east of Jakobshavns Isbræ show negligible change over the same period; but further south, at latitude 65 N, the western part of the ice sheet appears to have thickened by up to 2 m between 1980 and 1993. It is clear that such measurements must be continued over many years, both to quantify the effects of inter-annual variability and to measure long-term trends. To this end, we plan to complete a first survey of all major drainage basins on the ice sheet in May-June 1994, and then to resurvey all flight lines at 5a intervals, with more frequent flights over selected routes.

scholarly journals First point measurements of ice-sheet thickness change in Antarctica

1998 ◽  
Vol 27 ◽  
pp. 125-129 ◽  
Author(s):  
Gordon S. Hamilton ◽  
Ian M. Whillans ◽  
Peter J. Morgan
Keyword(s):  
Ice Sheet ◽  
Sheet Thickness ◽  
Snow Accumulation ◽  
Repeated Measurements ◽  
Occupation Times ◽  
Thickness Change ◽  
Global Positioning ◽  
First Results ◽  
Ice Stream B

Ice-sheet thickening or thinning rates in Antarctica are measured using the “coffee-can” or “submergence velocity” method. in this, repeated measurements of the positions of firn anchors are obtained using the global positioning system (GPS). The thickness change is (lie difference between vertical velocity so obtained and long-term rate of snow accumulation. Minor corrections for firn settling and downslopc motion are made. The technique avoids difficulties of short-term fluctuations in snowfall or snow den-sification. The result for Byrd Station is near balance, -0.004 (0.022) ma−1, and for the Dragon, just outboard of Ice Stream B, thinning at -0.096 (0.044) ma−1. Uncertainties with these first results are mainly due to the short occupation times during the first GPS surveys.

scholarly journals Are longitudinal ice-surface structures on the Antarctic Ice Sheet indicators of long-term ice-flow configuration?

2014 ◽  
Vol 2 (2) ◽  
pp. 911-933 ◽  
Author(s):  
N. F. Glasser ◽  
S. J. A. Jennings ◽  
M. J. Hambrey ◽  
B. Hubbard
Keyword(s):  
Flow Line ◽  
Ice Sheet ◽  
Surface Structures ◽  
Surface Velocity ◽  
Ice Flow ◽  
Antarctic Ice Sheet ◽  
Ice Surface ◽  
Ice Stream ◽  
The Antarctic

Abstract. Continent-wide mapping of longitudinal ice-surface structures on the Antarctic Ice Sheet reveals that they originate in the interior of the ice sheet and are arranged in arborescent networks fed by multiple tributaries. Longitudinal ice-surface structures can be traced continuously down-ice for distances of up to 1200 km. They are co-located with fast-flowing glaciers and ice streams that are dominated by basal sliding rates above tens of m yr-1 and are strongly guided by subglacial topography. Longitudinal ice-surface structures dominate regions of converging flow, where ice flow is subject to non-coaxial strain and simple shear. Associating these structures with the AIS' surface velocity field reveals (i) ice residence times of ~ 2500 to 18 500 years, and (ii) undeformed flow-line sets for all major flow units analysed except the Kamb Ice Stream and the Institute and Möller Ice Stream areas. Although it is unclear how long it takes for these features to form and decay, we infer that the major ice-flow and ice-velocity configuration of the ice sheet may have remained largely unchanged for several thousand years, and possibly even since the end of the last glacial cycle. This conclusion has implications for our understanding of the long-term landscape evolution of Antarctica, including large-scale patterns of glacial erosion and deposition.

Unearthing the forgotten record of glacier change in southeast Greenland

2020 ◽  
Author(s):  
Michael Cooper ◽  
Paulina Lewinska ◽  
Julian Dowdeswell ◽  
Edwin Hancock ◽  
William Smith ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Quantitative Information ◽  
Glacier Change ◽  
Regular Time ◽  
History Of ◽  
Long Term Trends ◽  
Surface Profiles ◽  
Volume Estimates

<p>Prior to the satellite era (pre-1970s) knowledge of long-term glacier change is sparse. Although some glacier-wide mass balance datasets are available, few records extend beyond twenty years in length, or indeed, start prior to the 1980s; as such, identifying long-term trends between glacier change and global temperatures is difficult. As a result, extending the record of glacier change will not only help to identify such trends, but may also facilitate more robust understanding of future glacier response under a perturbed and varying climate.</p><p>Since the ‘heroic age of Arctic (and Antarctic) exploration’, many photographs of polar environments have been captured and stored for historic interest. These photographs, depicting images of past glaciers and ice sheet margins, have, as of yet, untapped potential to provide important insights into past glacier extent, and long-term behaviour.</p><p>Using computer-vision methodologies, we present a unique record of georeferenced 3-D elevation models using declassified aerial imagery dating from the 1930s—1980s at quasi-regular time steps. This study focusses upon two sections (ca. 190 km total length) of the southeast margin of the Greenland Ice Sheet (in the vicinity of Kangerlussuaq Glacier), capturing the history of both land- and marine-terminating outlet glaciers, and local glaciers. We examine quantitative information extracted from these reconstructions, allowing us to ‘back extend’ the record of glacial change in this region, by measuring changes in glacial extent, surface profiles and height (elevation), and calculating volume estimates.</p>

scholarly journals Long-term trends in evapotranspiration and runoff over the drainage basins of the Gulf of Mexico during 1901-2008

2013 ◽  
Vol 49 (4) ◽  
pp. 1988-2012 ◽  
Author(s):  
Mingliang Liu ◽  
Hanqin Tian ◽  
Qichun Yang ◽  
Jia Yang ◽  
Xia Song ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Drainage Basins ◽  
Long Term Trends

High-Resolution Ground-Based GPS Measurements Show Intercampaign Bias in ICESat Elevation Data Near Summit, Greenland

2011 ◽  
Vol 49 (6) ◽  
pp. 3393-3400 ◽  
Author(s):  
Matthew R. Siegfried ◽  
Robert L. Hawley ◽  
John F. Burkhart
Keyword(s):  
Ground Truth ◽  
Laser Altimeter ◽  
Ice Cloud ◽  
Ice Surface ◽  
Salt Flats ◽  
Laser Signal ◽  
Elevation Data ◽  
Elevation Changes ◽  
Validation Experiments

The Geoscience Laser Altimeter System (GLAS) aboard the National Aeronautics and Space Administration's Ice, Cloud, and land Elevation Satellite (ICESat) collected data from early 2003 to late 2009 with the specific goal of measuring ice-surface elevation changes. While the precision of GLAS instrumentation has been studied over its intended target (ice), its accuracy has only been robustly estimated using independent (terrestrial nonlaser) methods over salt flats. Here, we perform repeat high-precision Global Positioning System (GPS) surveys under four passes of ICESat track 0412 (campaigns L3I, L3J, L2D, and L2E) to compare directly GLAS elevation data footprints to a coincident GPS ground truth near Summit, Greenland. Analysis and comparison of GLAS data with GPS data show a campaign-dependent elevation bias ranging from -0.112 ±0.030 m (L3J) to 0.121 ± 0.071 m (L2E). Although uncorrected reflectance values and field observations both indicate that forward scattering of the laser signal through the atmosphere accounts for the anomalously negative L3J bias, the biases of all campaigns studied are within the instrument's goal accuracy of ±0.15 m. However, our analysis shows a campaign dependence in the bias, which may propagate through estimates of mass balance. The error introduced from intercampaign biases illustrates the importance of long-term independent validation experiments of satellite altimetry data over ice sheets.

scholarly journals Improved retrieval of land ice topography from CryoSat-­2 data and its impact for volume change estimation of the Greenland Ice Sheet

2016 ◽  
Author(s):  
Johan Nilsson ◽  
Alex Gardner ◽  
Louise Sandberg Sørensen ◽  
Rene Forsberg
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Lower Sensitivity ◽  
Volume Changes ◽  
Near Surface ◽  
Ice Cloud ◽  
Ice Surface ◽  
Airborne Laser ◽  
Elevation Changes ◽  
New Processing

Abstract. A new methodology for retrieval of glacier and ice sheet elevations and elevation changes from CryoSat-2 data is presented. Surface elevations and elevation changes determined using this approach show significant improvements over ESA's publically available Cryosat-2 elevation product (L2 Baseline-B). This when compared to near-coincident airborne laser altimetry from NASA's Operation IceBridge and seasonal height amplitudes from the Ice, Cloud, and Elevation Satellite (ICESat). Applying this methodology to CryoSat-2 data collected in Interferometric Synthetic Aperture mode over the high relief regions of the Greenland ice sheet we find an improvement in the root-mean-square-error (RMSE) of 27 % and 40 % compared to ESA's L2 product in the derived elevation and elevation changes, respectively. In the interior part of the ice sheet, where CryoSat-2 operates in Low Resolution Mode, we find an improvement in the RMSE of 68 % and 55 % in the derived elevation and elevation changes, respectively. There is also an 86 % improvement in the magnitude of the seasonal amplitudes when compared to amplitudes derived from ICESat data. These results indicate that the new methodology provides improved tracking of the snow/ice surface with lower sensitivity to changes in near-surface dielectric properties. To demonstrate the utility of the new processing methodology we produce elevations, elevation changes and total volume changes from Cryosat-2 data for Greenland Ice Sheet during the period Jan-2011 to Jan-2015. We find that the Greenland Ice Sheet decreased in volume at rate of 289 ± 16 km3 a−1, with high inter-annual variability and spatial heterogeneity in rates of loss. This rate is 65 km3 a−1 more negative than rates determined from ESA's L2 product, highlighting the importance of Cryosat-2 processing methodologies.

scholarly journals Sea-ice surface roughness estimates from airborne laser scanner and laser altimeter observations in Fram Strait and north of Svalbard

2015 ◽  
Vol 56 (69) ◽  
pp. 235-244 ◽  
Author(s):  
Justin F. Beckers ◽  
Angelika H.H. Renner ◽  
Gunnar Spreen ◽  
Sebastian Gerland ◽  
Christian Haas
Keyword(s):  
Surface Roughness ◽  
Sea Ice ◽  
Laser Scanner ◽  
Ice Thickness ◽  
Fram Strait ◽  
Laser Altimeter ◽  
Airborne Laser Scanner ◽  
Ice Surface ◽  
Airborne Laser ◽  
Ice Surface Roughness

AbstractWe present sea-ice surface roughness estimates, i.e. the standard deviation of relative surface elevation, in the Arctic regions of Fram Strait and the Nansen Basin north of Svalbard acquired by an airborne laser scanner and a single-beam laser altimeter in 2010. We compare the scanner to the altimeter and compare the differences between the two survey regions. We estimate and correct sensor roll from the scanner data using the hyperbolic response of the scanner over a flat surface. Measurement surveys had to be longer than 5 km north of Svalbard and longer than 15 km in Fram Strait before the statistical distribution in surface roughness from the scanner and altimeter became similar. The shape of the surface roughness probability distributions agrees with those of airborne electromagnetic induction measurements of ice thickness. The ice in Fram Strait had a greater mean surface roughness, 0.16 m vs 0.09 m, and a wider distribution in roughness values than the ice in the Nansen Basin. An increase in surface roughness with increasing ice thickness was observed over fast ice found in Fram Strait near the coast of Greenland but not for the drift ice.

scholarly journals Improved retrieval of land ice topography from CryoSat-2 data and its impact for volume-change estimation of the Greenland Ice Sheet

2016 ◽  
Vol 10 (6) ◽  
pp. 2953-2969 ◽  
Author(s):  
Johan Nilsson ◽  
Alex Gardner ◽  
Louise Sandberg Sørensen ◽  
Rene Forsberg
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Lower Sensitivity ◽  
Volume Changes ◽  
Near Surface ◽  
Ice Cloud ◽  
Ice Surface ◽  
Airborne Laser ◽  
Elevation Changes ◽  
New Processing

Abstract. A new methodology for retrieval of glacier and ice sheet elevations and elevation changes from CryoSat-2 data is presented. Surface elevations and elevation changes determined using this approach show significant improvements over ESA's publicly available CryoSat-2 elevation product (L2 Baseline-B). The results are compared to near-coincident airborne laser altimetry from NASA's Operation IceBridge and seasonal height amplitudes from the Ice, Cloud, and Elevation Satellite (ICESat). Applying this methodology to CryoSat-2 data collected in interferometric synthetic aperture mode (SIN) over the high-relief regions of the Greenland Ice Sheet we find an improvement in the root-mean-square error (RMSE) of 27 and 40 % compared to ESA's L2 product in the derived elevation and elevation changes, respectively. In the interior part of the ice sheet, where CryoSat-2 operates in low-resolution mode (LRM), we find an improvement in the RMSE of 68 and 55 % in the derived elevation and elevation changes, respectively. There is also an 86 % improvement in the magnitude of the seasonal amplitudes when compared to amplitudes derived from ICESat data. These results indicate that the new methodology provides improved tracking of the snow/ice surface with lower sensitivity to changes in near-surface dielectric properties. To demonstrate the utility of the new processing methodology we produce elevations, elevation changes, and total volume changes from CryoSat-2 data for the Greenland Ice Sheet during the period January 2011 to January 2015. We find that the Greenland Ice Sheet decreased in volume at a rate of 289 ± 20 km3a−1, with high interannual variability and spatial heterogeneity in rates of loss. This rate is 65 km3a−1 more negative than rates determined from ESA's L2 product, highlighting the importance of CryoSat-2 processing methodologies.

scholarly journals Geodetic airborne laser altimetry of Breidamerkurjökull and Skeidarárjökull, Iceland, and Jakobshavns Isbræ, West Greenland

1993 ◽  
Vol 17 ◽  
pp. 379-385 ◽  
Author(s):  
James B. Garvin ◽  
Richard S. Williams
Keyword(s):  
Global Positioning System ◽  
Spatial Density ◽  
Strain Rates ◽  
Laser Altimetry ◽  
Laser Altimeter ◽  
Long Wavelength ◽  
Airborne Laser ◽  
Surface Slopes ◽  
Global Positioning ◽  
Longitudinal Strain Rate

Two geodetic airborne laser altimeter (ALA) systems coupled to Global Positioning System receivers acquired submeter-resolution topographic profiles of the lower parts of Breidamerkurjökull and Skeidarárjökull, Iceland, in May 1989 and September 1991 (Skeidarárjökull) and of Jakobshavns Isbræ, Greenland, in April 1992. Maximum measured crevasse depths on Breidamerkurjökull, Skeidarárjökull and Jakobshavns Isbræ were 20.7, 36.1 and 50.2 m, respectively. Crevasse spacings were 43 m (45 crevasses km−1) for Breidamerkur jökull, 46–51 m (25 crevasses km−1) for Skeidarárjökull and 20–40 m (lower part) or 50–80 m (upper part) of Jakobshavns Isbræ (27 crevasses km−1). Surface slopes were ~2.4° for the lower 11 km of Breidamerkurjökull, ~0.8° for the lower 10 km of Skeidarárjökull and 1.55° for the lower 28 km of Jakobshavns Isbræ (with a range of 0.55° for the final 17 km to ~6.3° for a steep central part several km in length). Average longitudinal strain-rate values, estimated by assuming a bulk ice temperature of 0°C and a density of 880 kg m−3, ranged from 0.12 a−1 for Breidamerkurjökull, to 0.63 a−1 for Skeidarárjökull; values for Jakobshavns Isbræ fell between 1.3 and 1.7 a−1. Remote sensing of glacier microtopography by ALA offers a potential new tool for determining crevasse morphology, spatial density and spacing, meter-scale local slopes, long-wavelength gradients and derived strain rates.

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