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 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 Elevation and Volume Changes in Greenland Ice Sheet From 2010 to 2019 Derived From Altimetry Data

2021 ◽  
Vol 9 ◽  
Author(s):  
Guodong Chen ◽  
Shengjun Zhang ◽  
Shenghao Liang ◽  
Jiaheng Zhu
Keyword(s):  
Volume Change ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Altimetry Data ◽  
Elevation Change ◽  
Volume Changes ◽  
Change Rate ◽  
Ice Cloud ◽  
Elevation Changes ◽  
Elevation Difference

Long-term altimetry data are one of the major sources to analyze the change in global ice reserves. This study focuses on the elevation and volume changes in the Greenland ice sheet (GrIS) from 2010 to 2019 derived from altimetry observations. In this study, the methods for determining surface elevation change rates are discussed, and specific strategies are designed. A new elevation difference method is proposed for CryoSat-2 synthetic aperture interferometric (SARin) mode observations. Through validation with Airborne Topographic Mapper (ATM) data, this new method is proved to be effective for slope terrains at the margins of the ice sheet. Meanwhile, a surface fit method is applied for the flat interior of the ice sheet where low resolution mode (LRM) observations are provided. The results of elevation change rates in the GrIS from 2010 to 2019 are eventually calculated by combining CryoSat-2 and ATM observations. An elevation change rate of −11.83 ± 1.14 cm·a−1 is revealed, corresponding to a volume change rate of −200.22 ± 18.26 km3·a−1. The results are compared with the elevation changes determined by Ice, Cloud, and Land Elevation Satellite (ICESat) from 2003 to 2009. Our results show that the overall volume change rate in the GrIS slowed down by approximately 10% during the past decade, and that the main contributor of GrIS ice loss has shifted from the southeast coast to the west margin of the ice sheet.

scholarly journals Circum-Greenland, ice-thickness measurements collected during PROMICE airborne surveys in 2007, 2011 and 2015

2018 ◽  
pp. 79-82 ◽  
Author(s):  
Louise Sandberg Sørensen ◽  
Sebastian B. Simonsen ◽  
René Forsberg ◽  
Lars Stenseng ◽  
Henriette Skourup ◽  
...  
Keyword(s):  
Mass Loss ◽  
Laser Scanning ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Thickness ◽  
Average Mass ◽  
Airborne Laser ◽  
Elevation Changes ◽  
Ice Velocity ◽  
Thickness Measurements

The Greenland ice sheet has experienced an average mass loss of 142 ± 49 Gt/yr from 1992 to 2011 (Shepherd et al. 2012), making it a significant contributor to sea-level rise. Part of the ice- sheet mass loss is the result of increased dynamic response of outlet glaciers (Rignot et al. 2011). The ice discharge from outlet glaciers can be quantified by coincident measurements of ice velocity and ice thickness (Thomas et al. 2000; van den Broeke et al. 2016). As part of the Programme for monitoring of the Greenland Ice Sheet (PROMICE; Ahlstrøm et al. 2008), three airborne surveys were carried out in 2007, 2011 and 2015, with the aim of measuring the changes in Greenland ice-sheet thicknesses. The purpose of the airborne surveys was to collect data to assess the dynamic mass loss of the Greenland ice sheet (Andersen et al. 2015). Here, we present these datasets of observations from ice-penetrating radar and airborne laser scanning, which, in combination, make us able to determine the ice thickness precisely. Surface-elevation changes between surveys are also presented, although we do not provide an in-depth scientific interpretation of these.

scholarly journals Dynamic inland propagation of thinning due to ice loss at the margins of the Greenland ice sheet

2012 ◽  
Vol 58 (210) ◽  
pp. 734-740 ◽  
Author(s):  
Weili Wang ◽  
Jun Li ◽  
H. Jay Zwally
Keyword(s):  
Mass Loss ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Large Mass ◽  
Dynamic Impact ◽  
Ice Flow ◽  
Ice Cloud ◽  
Elevation Changes ◽  
Balance Analysis

AbstractMass-balance analysis of the Greenland ice sheet based on surface elevation changes observed by the European Remote-sensing Satellite (ERS) (1992-2002) and Ice, Cloud and land Elevation Satellite (ICESat) (2003-07) indicates that the strongly increased mass loss at lower elevations (<2000 m) of the ice sheet, as observed during 2003-07, appears to induce interior ice thinning at higher elevations. In this paper, we perform a perturbation experiment with a three-dimensional anisotropic ice-flow model (AIF model) to investigate this upstream propagation. Observed thinning rates in the regions below 2000 m elevation are used as perturbation inputs. The model runs with perturbation for 10 years show that the extensive mass loss at the ice-sheet margins does in fact cause interior thinning on short timescales (i.e. decadal). The modeled pattern of thinning over the ice sheet agrees with the observations, which implies that the strong mass loss since the early 2000s at low elevations has had a dynamic impact on the entire ice sheet. The modeling results also suggest that even if the large mass loss at the margins stopped, the interior ice sheet would continue thinning for 300 years and would take thousands of years for full dynamic recovery.

scholarly journals First spectral measurements of light attenuation in Greenland Ice Sheet bare ice suggest shallower subsurface radiative heating and ICESat-2 penetration depth in the ablation zone

2020 ◽  
Author(s):  
Matthew G. Cooper ◽  
Laurence C. Smith ◽  
Asa K. Rennermalm ◽  
Marco Tedesco ◽  
Rohi Muthyala ◽  
...  
Keyword(s):  
Light Transmission ◽  
Light Attenuation ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Radiative Heating ◽  
Ablation Zone ◽  
Field Site ◽  
Attenuation Coefficients ◽  
Near Surface ◽  
Ice Surface

Abstract. Light transmission into bare glacial ice affects surface energy balance, bio-photochemical cycling, and light detection and ranging (LiDAR) laser elevation measurements but has not previously been reported for the Greenland Ice Sheet. We present in-ice solar irradiance measured over the spectral range 350–900 nm and 12–77 cm depth collected at a site in the western Greenland ablation zone. The acquired spectral irradiance measurements are used to calculate flux attenuation coefficients using an exponential decay Bouguer law model and are compared to values calculated from two-stream radiative transfer theory. Relative to asymptotic two-stream theory, our empirical attenuation coefficients are up to one order of magnitude larger in the range 350–530 nm, suggesting light absorbing particles embedded in ice enhance visible light absorption at our field site. The empirical coefficients accurately describe light attenuation in the ice interior but underestimate light attenuation near the ice surface. Consequently, Bouguer’s law overestimates transmitted flux by up to 50 % depending on wavelength. Refraction is unlikely to explain the discrepancy. Instead, vertical variation in the ice microstructure and the concentration of light absorbing particles appears to enhance near-surface attenuation at our field site. The magnitude of this near-surface attenuation implies that optical penetration depth is lower by up to 19 cm (28 %) at wavelengths relevant to visible-wavelength lidar altimetry of ice surface elevation (e.g. 532 nm for the Ice, Cloud, and Land Elevation Satellite-2) than is suggested by e-folding depths inferred from two stream theory for optically pure glacier ice. This enhanced near-surface attenuation implies shallower light transmission and therefore lower subsurface light availability for subsurface radiative heating and bio-photochemical cycling. We recommend radiative transfer models applied to bare ice in the Greenland Ice Sheet ablation zone account for vertical variation in light attenuation due to the vertical distribution of light absorbing particles and ice microstructure, and we provide new values of flux attenuation, absorption, and scattering coefficients to support model validation and parameterization.

scholarly journals Greenland ice-sheet surface properties observed by the Seasat-A scatterometer at enhanced resolution

1994 ◽  
Vol 40 (135) ◽  
pp. 213-230 ◽  
Author(s):  
David G. Long ◽  
Mark R. Drinkwater
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Base Line ◽  
Near Surface ◽  
Scatter Coefficient ◽  
Ice Surface ◽  
Microwave Radar ◽  
Enhanced Resolution ◽  
Wet Snow ◽  
A New Technique

AbstractFor 3 months in 1978, the 14.6 GHz Seasat-A scatterometer (SASS) measured the normalized microwave-radar back-scatter coefficient of the Earth’s surface for the purpose of estimating near-surface vector winds over the ocean. SASS also made back-scatter measurements over land and ice regions; however, the application of this data has been limited due to the low (50 km) resolution of the measurements. Using a new technique for generating 6 km enhanced-resolution SASS images of the radar back-scatter characteristics, we present a study of the 1978 condition of the Greenland ice sheet. We derive a time-series of back-scatter images spanning the period July–September 1978. These images show the extent of summer ablation along the ice-sheet periphery. Using the data and models relating firn structure and condition to radar back-scatter characteristics, we delineate and map the seasonal extent of zones which appear to correspond to dry-snow, percolation, wet-snow, and ablation facies, over virtually the entire ice sheet. The results provide a base line with which to compare current (ERS-1) and future Greenland radar maps of snow-and ice-surface conditions.

scholarly journals Elevation changes on the Greenland ice sheet from comparison of aircraft and ICESat laser-altimeter data

2005 ◽  
Vol 42 ◽  
pp. 77-82 ◽  
Author(s):  
R. Thomas ◽  
E. Frederick ◽  
W. Krabill ◽  
S. Manizade ◽  
C. Martin ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Altimeter Data ◽  
Aircraft Measurements ◽  
Drainage Basins ◽  
Laser Altimeter ◽  
Ice Cloud ◽  
Spatial Coverage ◽  
First Results ◽  
Elevation Changes

AbstractPrecise measurements of surface elevation on the Greenland ice sheet have been made almost every year since 1991 by an airborne scanning laser altimeter operated by NASA/Wallops Flight Facility. Results show substantial thinning over large areas near the coast, with a general increase in thinning rates since 1997, in the drainage basins of thinning glaciers, and a recent thickening in the southeast associated with very high snowfall in this region during 2003. Here, we present first results from the comparison of the aircraft data with similar measurements from the laser altimeter aboard NASA’s Ice, Cloud and land Elevation Satellite (ICESat), which was launched in January 2003. These show very close agreement with results inferred solely from the aircraft measurements, indicating that accuracies are similar for both datasets. Broad spatial coverage by satellite, together with the baseline dataset of aircraft measurements, offers the prospects of routine surveys of ice-sheet elevation changes by ICESat and follow-on missions.

scholarly journals Greenland ice-sheet surface properties observed by the Seasat-A scatterometer at enhanced resolution

1994 ◽  
Vol 40 (135) ◽  
pp. 213-230 ◽  
Author(s):  
David G. Long ◽  
Mark R. Drinkwater
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Base Line ◽  
Near Surface ◽  
Scatter Coefficient ◽  
Ice Surface ◽  
Microwave Radar ◽  
Enhanced Resolution ◽  
Wet Snow ◽  
A New Technique

AbstractFor 3 months in 1978, the 14.6 GHz Seasat-A scatterometer (SASS) measured the normalized microwave-radar back-scatter coefficient of the Earth’s surface for the purpose of estimating near-surface vector winds over the ocean. SASS also made back-scatter measurements over land and ice regions; however, the application of this data has been limited due to the low (50 km) resolution of the measurements. Using a new technique for generating 6 km enhanced-resolution SASS images of the radar back-scatter characteristics, we present a study of the 1978 condition of the Greenland ice sheet. We derive a time-series of back-scatter images spanning the period July–September 1978. These images show the extent of summer ablation along the ice-sheet periphery. Using the data and models relating firn structure and condition to radar back-scatter characteristics, we delineate and map the seasonal extent of zones which appear to correspond to dry-snow, percolation, wet-snow, and ablation facies, over virtually the entire ice sheet. The results provide a base line with which to compare current (ERS-1) and future Greenland radar maps of snow-and ice-surface conditions.

scholarly journals The Greenland ice sheet – snowline elevations at the end of the melt seasons from 2000 to 2017

2018 ◽  
pp. 71-74
Author(s):  
Robert S. Fausto And the PROMICE team*
Keyword(s):  
Mass Loss ◽  
Laser Scanning ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Thickness ◽  
Average Mass ◽  
Dynamic Mass ◽  
Airborne Laser ◽  
Elevation Changes ◽  
Ice Velocity

The Greenland ice sheet has experienced an average mass loss of 142 ± 49 Gt/yr from 1992 to 2011 (Shepherd et al. 2012), making it a significant contributor to sea-level rise. Part of the ice- sheet mass loss is the result of increased dynamic response of outlet glaciers (Rignot et al. 2011). The ice discharge from outlet glaciers can be quantified by coincident measurements of ice velocity and ice thickness (Thomas et al. 2000; van den Broeke et al. 2016). As part of the Programme for monitoring of the Greenland Ice Sheet (PROMICE; Ahlstrøm et al. 2008), three airborne surveys were carried out in 2007, 2011 and 2015, with the aim of measuring the changes in Greenland ice-sheet thicknesses. The purpose of the airborne surveys was to collect data to assess the dynamic mass loss of the Greenland ice sheet (Andersen et al. 2015). Here, we present these datasets of observations from ice-penetrating radar and airborne laser scanning, which, in combination, make us able to determine the ice thickness precisely. Surface-elevation changes between surveys are also presented, although we do not provide an in-depth scientific interpretation of these.

Estimating near-surface climatology of multi-reanalyses over the Greenland Ice Sheet

2021 ◽  
pp. 105676
Author(s):  
Wuying Zhang ◽  
Yetang Wang ◽  
Paul C.J.P. Smeets ◽  
Carleen H. Reijmer ◽  
Baojuan Huai ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Near Surface
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