scholarly journals Satellite Altimetry, Semivariograms, and Seasonal Elevation Changes in the Ablation Zone of West Greenland

1990 ◽  
Vol 14 ◽  
pp. 158-163 ◽  
Author(s):  
Craig S. Lingle ◽  
Anita C. Brenner ◽  
H. Jay Zwally
Keyword(s):  
Noise Level ◽  
Satellite Altimetry ◽  
Ice Sheet ◽  
Surface Elevation ◽  
Altimeter Data ◽  
Ablation Zone ◽  
Radar Altimeter ◽  
West Greenland ◽  
Elevation Changes ◽  
The Mean

Seasonal mean changes in the surface elevation of the ablation zone of West Greenland to 72°N between spring 1985 and summer 1986 are measured using radar altimeter data from the 18-month Geosat Geodetic Mission. Semi-variograms are used to estimate the noise in the data as a function of position on the ice sheet. Mean elevation changes are computed by averaging the elevation differences measured at points where orbits ascending in latitude are later crossed by orbits descending in latitude (or the reverse), with each cross-over difference weighted in proportion to the inverse square of the noise level in the neighborhood of the cross-over point. The mean surface elevation of the ablation zone, relative to spring 1985, ranged from 1.5 ± 0.6 m lower during summer 1985 to 1.7 ± 0.4 m higher during spring 1986.

scholarly journals Satellite Altimetry, Semivariograms, and Seasonal Elevation Changes in the Ablation Zone of West Greenland

1990 ◽  
Vol 14 ◽  
pp. 158-163 ◽  
Author(s):  
Craig S. Lingle ◽  
Anita C. Brenner ◽  
H. Jay Zwally
Keyword(s):  
Noise Level ◽  
Satellite Altimetry ◽  
Ice Sheet ◽  
Surface Elevation ◽  
Altimeter Data ◽  
Ablation Zone ◽  
Radar Altimeter ◽  
West Greenland ◽  
Elevation Changes ◽  
The Mean

Seasonal mean changes in the surface elevation of the ablation zone of West Greenland to 72°N between spring 1985 and summer 1986 are measured using radar altimeter data from the 18-month Geosat Geodetic Mission. Semi-variograms are used to estimate the noise in the data as a function of position on the ice sheet. Mean elevation changes are computed by averaging the elevation differences measured at points where orbits ascending in latitude are later crossed by orbits descending in latitude (or the reverse), with each cross-over difference weighted in proportion to the inverse square of the noise level in the neighborhood of the cross-over point. The mean surface elevation of the ablation zone, relative to spring 1985, ranged from 1.5 ± 0.6 m lower during summer 1985 to 1.7 ± 0.4 m higher during spring 1986.

scholarly journals An improved elevation dataset for climate and ice-sheet modelling: validation with satellite imagery

1997 ◽  
Vol 25 ◽  
pp. 439-444 ◽  
Author(s):  
J. L. Bamber ◽  
R. A. Bindschadler
Keyword(s):  
High Resolution ◽  
General Circulation ◽  
Global Climate ◽  
Ice Sheet ◽  
General Circulation Models ◽  
Horizontal Resolution ◽  
Surface Elevation ◽  
Altimeter Data ◽  
Ice Thickness ◽  
Radar Altimeter

Recent studies by several groups have indicated that the performance of general circulation models (GCMs) over the ice sheets is severely limited by the relatively low resolution of the models at the margins, where surface slopes are greatest. To provide accurate energy-budget estimates, resolutions of better than 0.5° are desirable, requiring nested or multiple gridding and accurate, high-resolution boundary conditions. Here we present a new, high-resolution (5 km) digital elevation model for the Antarctic ice sheet, derived from radar-altimeter data obtained from the geodetic phase of the satellite, ERS-1. These data have been combined with the revised ice-thickness grid reported in Bamber and Huybrechts (1996) to produce a bed- and surface-elevation dataset for use in regional and global climate and paleo-climaie modelling applications. The real level of spatial detail in the datasets has been examined with the aid of Landsat Thematic Mapper data. Imagery around Ice Stream D, West Antarctica, shows that the revised ice-thickness grid is accurately geolocated, and contains valuable fine-scale topographic detail beyond that available from the cartographic version of the data (Drewry, 1983). The surface topography in the region of the Ross Ice Shelf has been used to illustrate the level of detail in both the vertical and horizontal resolution of (he surface dataset. Laudsat data has also been used to examine features in the surface-elevation data. In particular, the location of the grounding zone, for Ice Streams D and E, derived from the two data sources shows good agreement. The results of this validation underscore the utility of the new datasets for high-resolution modelling, and highlight the limitations of the Folio maps for such applications.

scholarly journals Boundary conditions of an active West Antarctic subglacial lake: implications for storage of water beneath the ice sheet

2013 ◽  
Vol 7 (3) ◽  
pp. 2979-2999 ◽  
Author(s):  
M. J. Siegert ◽  
N. Ross ◽  
H. Corr ◽  
B. Smith ◽  
T. Jordan ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Surface Elevation ◽  
Altimeter Data ◽  
Radar Altimeter ◽  
Local Flow ◽  
Antarctic Ice Sheet ◽  
Subglacial Lake ◽  
West Antarctic ◽  
Ice Surface ◽  
The Antarctic

Abstract. Repeat-pass IceSat altimetry has revealed 124 discrete surface height changes across the Antarctic Ice Sheet, interpreted to be caused by subglacial lake discharges (surface lowering) and inputs (surface uplift). Few of these active lakes have been confirmed by radio-echo sounding (RES) despite several attempts (notable exceptions are Lake Whillans and three in the Adventure Subglacial Trench). Here we present targeted RES and radar altimeter data from an "active lake" location within the upstream Institute Ice Stream, into which 0.12 km3 of water is calculated to have flowed between October 2003 and February 2008. We use a series of transects to establish an accurate appreciation of the influences of bed topography and ice-surface elevation on water storage potential. The location of surface height change is over the downslope flank of a distinct topographic hollow, where RES reveals no obvious evidence for deep (> 10 m) water. The regional hydropotential reveals a sink coincident with the surface change, however. Governed by the location of the hydrological sink, basal water will likely "drape" over existing topography in a manner dissimilar to subglacial lakes where flat strong specular RES reflections are measured. The inability of RES to detect the active lake means that more of the Antarctic ice sheet bed may contain stored water than is currently appreciated. Variation in ice surface elevation datasets leads to significant alteration in calculations of the local flow of basal water indicating the value of, and need for, high resolution RES datasets in both space and time to establish and characterise subglacial hydrological processes.

scholarly journals Four decades of Antarctic surface elevation changes from multi-mission satellite altimetry

2019 ◽  
Vol 13 (2) ◽  
pp. 427-449 ◽  
Author(s):  
Ludwig Schröder ◽  
Martin Horwath ◽  
Reinhard Dietrich ◽  
Veit Helm ◽  
Michiel R. van den Broeke ◽  
...  
Keyword(s):  
Time Series ◽  
Satellite Altimetry ◽  
Average Rate ◽  
Ice Sheet ◽  
Surface Elevation ◽  
Antarctic Ice Sheet ◽  
Mission Satellite ◽  
Elevation Changes ◽  
Dronning Maud Land ◽  
The Antarctic

Abstract. We developed a multi-mission satellite altimetry analysis over the Antarctic Ice Sheet which comprises Seasat, Geosat, ERS-1, ERS-2, Envisat, ICESat and CryoSat-2. After a consistent reprocessing and a stepwise calibration of the inter-mission offsets, we obtained monthly grids of multi-mission surface elevation change (SEC) with respect to the reference epoch 09/2010 (in the format of month/year) from 1978 to 2017. A validation with independent elevation changes from in situ and airborne observations as well as a comparison with a firn model proves that the different missions and observation modes have been successfully combined to a seamless multi-mission time series. For coastal East Antarctica, even Seasat and Geosat provide reliable information and, hence, allow for the analysis of four decades of elevation changes. The spatial and temporal resolution of our result allows for the identification of when and where significant changes in elevation occurred. These time series add detailed information to the evolution of surface elevation in such key regions as Pine Island Glacier, Totten Glacier, Dronning Maud Land or Lake Vostok. After applying a density mask, we calculated time series of mass changes and found that the Antarctic Ice Sheet north of 81.5∘ S was losing mass at an average rate of -85±16 Gt yr−1 between 1992 and 2017, which accelerated to -137±25 Gt yr−1 after 2010.

scholarly journals Boundary conditions of an active West Antarctic subglacial lake: implications for storage of water beneath the ice sheet

2014 ◽  
Vol 8 (1) ◽  
pp. 15-24 ◽  
Author(s):  
M. J. Siegert ◽  
N. Ross ◽  
H. Corr ◽  
B. Smith ◽  
T. Jordan ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Surface Elevation ◽  
Altimeter Data ◽  
Radar Altimeter ◽  
Local Flow ◽  
Antarctic Ice Sheet ◽  
Subglacial Lake ◽  
West Antarctic ◽  
Ice Surface ◽  
The Antarctic

Abstract. Repeat-pass ICESat altimetry has revealed 124 discrete surface height changes across the Antarctic Ice Sheet, interpreted to be caused by subglacial lake discharges (surface lowering) and inputs (surface uplift). Few of these active lakes have been confirmed by radio-echo sounding (RES) despite several attempts (notable exceptions are Lake Whillans and three in the Adventure Subglacial Trench). Here we present targeted RES and radar altimeter data from an "active lake" location within the upstream Institute Ice Stream, into which at least 0.12 km3 of water was previously calculated to have flowed between October 2003 and February 2008. We use a series of transects to establish an accurate depiction of the influences of bed topography and ice surface elevation on water storage potential. The location of surface height change is downstream of a subglacial hill on the flank of a distinct topographic hollow, where RES reveals no obvious evidence for deep (> 10 m) water. The regional hydropotential reveals a sink coincident with the surface change, however. Governed by the location of the hydrological sink, basal water will likely "drape" over topography in a manner dissimilar to subglacial lakes where flat strong specular RES reflections are measured. The inability of RES to detect the active lake means that more of the Antarctic ice sheet bed may contain stored water than is currently appreciated. Variation in ice surface elevation data sets leads to significant alteration in calculations of the local flow of basal water indicating the value of, and need for, high-resolution altimetry data in both space and time to establish and characterise subglacial hydrological processes.

scholarly journals Elevation changes on the East Antarctic ice sheet, 1978-93, from satellite radar altimetry: a preliminary assessment

1998 ◽  
Vol 27 ◽  
pp. 7-18 ◽  
Author(s):  
Craig S. Lingle ◽  
David N. Covey
Keyword(s):  
Ice Sheet ◽  
Time Frame ◽  
Rate Of Change ◽  
Altimeter Data ◽  
Late Winter ◽  
Time Interval ◽  
Radar Altimeter ◽  
Antarctic Ice Sheet ◽  
The Mean ◽  
East Antarctic Ice Sheet

Radar altimeter data from Seasal (1978), Geosat (1985-88) and ERS-1 (1991—93) are employed to estimate multi-year mean changes of the surface height throughout a region on the East Antarctic ice sheet (EAIS) extending to 72.1° S, the southernmost limit of coverage for Seasat and Geosat altimetry, and above 1500 m elevation, using orbit crossover analysis. The changes are estimated on a same-season (austral late-winter (ALW) toALW) basis, where ALW is the 10 July 9 October time-frame of the Seasat altimetry. Altimeter data corrected for slope-induced errors are used. Altimeter data not corrected for slope-induced errors are also used, for comparison. Intersatellite orbit bias, combined with the effect of other radial errors such as instrumental bias, is estimated using crossover differences on the offshore ALW sea ice, which is employed as a geoid-parallcl reference surface. If similar intersatellite radial biases are characteristic of the continental Antarctic ice-sheet altimetry to 72.1° S, the results of all crossover analyses adjusted for this intersatellite bias — suggest that the mean rate-of-change of the surface height between Seasat and Geosat for ALWs 1978 to 1986-88 was with in the range +11 to -11 mm a−1. The bias-adjusted results of all crossover analyses between Seasat and ERS-1 suggest that the mean rate-of-change of the surface height between ALWs 1978 and 1991-93 was with in the range-17 to-55mma−1 (maximum intersatellitc bias estimate) or 0 to -40 mm a−1 (minimum bias estimate), suggesting that the surface may have lowered slightly during this time interval. The inconsistency of the adjusted Seasat to Geosat vs Seasat to ERS-1 results, however, may be an indication that orbits more accurate than JGM-2 are needed for estimation of regional multi-year mean changes of elevation on the EAIS. Alternatively, it may be a reflection of the differing orbit inclinations of Seasal and ERS-1.

scholarly journals Spatio-temporal analysis of surface elevation changes in Pine Island Glacier, Antarctica, from ICESat GLAS data and ERS-1 radar altimeter data

2014 ◽  
Vol 55 (66) ◽  
pp. 248-258 ◽  
Author(s):  
Ute C. Herzfeld ◽  
Bruce Wallin
Keyword(s):  
Temporal Analysis ◽  
Surface Elevation ◽  
Altimeter Data ◽  
Radar Altimeter ◽  
Elevation Change ◽  
Ice Shelf ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Elevation Changes ◽  
Spatio Temporal

AbstractCharacterized by fast movement, low surface slope and grounding below sea level, Pine Island Glacier (PIG) plays an important role in the stability of the West Antarctic ice sheet. In previous work, we reported that the spatial distribution of 1995–2003 surface lowering in PIG suggests an attribution of changes to an internally forced process in the glacier. Other work associates changes in PIG entirely with processes in its ice shelf. Here time series of maps of surface elevation change in PIG and its ice shelf are derived from geostatistical analysis of ICESat GLAS and ERS-1 radar altimeter data. Based on spatio-temporal analysis of 1995–2007 elevation change, we discuss indications of processes that initiate from changes in the ice shelf versus processes that start internally in the glacier. Thinning rates continued to increase after 2003, regionally to >15 m a–1. The initiation of acceleration occurred in the interior of the ice stream, while in later years largest elevation loss was driven by changes in the ice shelf and upward propagation. By 2006, the region of thinning had expanded up-glacier beyond the initial areas of surface lowering to 100 km above the hinge line. More than one process causes dynamically complex changes in PIG.

A new elevation change time series of the Antarctic Ice Sheet from Envisat and CryoSat-2 radar altimetry

2020 ◽  
Author(s):  
Baojun Zhang ◽  
Quanming Yang ◽  
Zemin Wang ◽  
Hong Geng ◽  
Jiachun An ◽  
...  
Keyword(s):  
Time Series ◽  
Satellite Altimetry ◽  
Ice Sheet ◽  
Least Square ◽  
Surface Elevation ◽  
The West ◽  
Antarctic Ice Sheet ◽  
West Antarctic ◽  
Elevation Changes ◽  
The Antarctic

<p>Satellite altimetry is an important data source for ice sheet change observation. The long-term time series of ice sheet changes can be obtained by combining satellite altimetry missions with similar sensor characteristics. Then, how to correct the inter-mission offsets becomes an important scientific issue. Review of previous studies, we found that the observations of satellite ascending and descending orbits also have an important influence on the estimation of inter-mission offsets. On this basis, have created a new least-square fitting mathematical model to estimate and correct the errors of ascending and descending orbits and inter-mission offsets by introducing the inter-mission offsets terms related to the observations of ascending and descending orbits. Utilizing this model, we developed a time series of monthly Antarctic ice sheet elevation changes of 5 km grid from May 2002 to April 2019. A validation with surface elevation from airborne observations and a comparison with surface elevation changes from ICESat proved that the proposed model can successfully estimate and correct the errors and be used to construct multi-mission surface elevation time series. Without a doubt, the temporal and spatial changes of Antarctic ice sheet elevation can be obtained from our monthly grid time series. From the time series, we find that over the period May 2002 to April 2019 the loss of ice and snow in the Antarctic ice sheet mainly occurred in the glaciers along the Amundsen coast in the West Antarctic and the Totten glacier in the East Antarctic, while the accumulation took place in Queen Maud of the East Antarctic. In May 2002, the Antarctic ice sheet experienced a volume loss of -71.4 ± 11.7 km<sup>3</sup>/yr, with an acceleration of –5.8 ± 1.2 km<sup>3</sup>/yr<sup>2</sup> over the period May 2002 to April 2019, including 45.0 ± 9.6 km<sup>3</sup>/yr and 0.1 ±1.0 km<sup>3</sup>/yr<sup>2</sup> for the East Antarctic ice sheet, -97.0 ± 4.4 km<sup>3</sup>/yr and -7.6 ±0.5 km<sup>3</sup>/yr<sup>2</sup> for the West Antarctic ice sheet and -19.5 ± 5.3 km<sup>3</sup>/yr and 1.7 ±0.5 km<sup>3</sup>/yr<sup>2</sup> for the Antarctic Peninsula ice sheet.</p>

scholarly journals Elevation changes on the East Antarctic ice sheet, 1978-93, from satellite radar altimetry: a preliminary assessment

1998 ◽  
Vol 27 ◽  
pp. 7-18 ◽  
Author(s):  
Craig S. Lingle ◽  
David N. Covey
Keyword(s):  
Ice Sheet ◽  
Time Frame ◽  
Rate Of Change ◽  
Altimeter Data ◽  
Late Winter ◽  
Time Interval ◽  
Radar Altimeter ◽  
Antarctic Ice Sheet ◽  
The Mean ◽  
East Antarctic Ice Sheet

Radar altimeter data from Seasal (1978), Geosat (1985-88) and ERS-1 (1991—93) are employed to estimate multi-year mean changes of the surface height throughout a region on the East Antarctic ice sheet (EAIS) extending to 72.1° S, the southernmost limit of coverage for Seasat and Geosat altimetry, and above 1500 m elevation, using orbit crossover analysis. The changes are estimated on a same-season (austral late-winter (ALW) toALW) basis, where ALW is the 10 July 9 October time-frame of the Seasat altimetry. Altimeter data corrected for slope-induced errors are used. Altimeter data not corrected for slope-induced errors are also used, for comparison. Intersatellite orbit bias, combined with the effect of other radial errors such as instrumental bias, is estimated using crossover differences on the offshore ALW sea ice, which is employed as a geoid-parallcl reference surface. If similar intersatellite radial biases are characteristic of the continental Antarctic ice-sheet altimetry to 72.1° S, the results of all crossover analyses adjusted for this intersatellite bias — suggest that the mean rate-of-change of the surface height between Seasat and Geosat for ALWs 1978 to 1986-88 was with in the range +11 to -11 mm a−1. The bias-adjusted results of all crossover analyses between Seasat and ERS-1 suggest that the mean rate-of-change of the surface height between ALWs 1978 and 1991-93 was with in the range-17 to-55mma−1 (maximum intersatellitc bias estimate) or 0 to -40 mm a−1 (minimum bias estimate), suggesting that the surface may have lowered slightly during this time interval. The inconsistency of the adjusted Seasat to Geosat vs Seasat to ERS-1 results, however, may be an indication that orbits more accurate than JGM-2 are needed for estimation of regional multi-year mean changes of elevation on the EAIS. Alternatively, it may be a reflection of the differing orbit inclinations of Seasal and ERS-1.

scholarly journals An improved elevation dataset for climate and ice-sheet modelling: validation with satellite imagery

1997 ◽  
Vol 25 ◽  
pp. 439-444 ◽  
Author(s):  
J. L. Bamber ◽  
R. A. Bindschadler
Keyword(s):  
High Resolution ◽  
General Circulation ◽  
Global Climate ◽  
Ice Sheet ◽  
General Circulation Models ◽  
Horizontal Resolution ◽  
Surface Elevation ◽  
Altimeter Data ◽  
Ice Thickness ◽  
Radar Altimeter

Recent studies by several groups have indicated that the performance of general circulation models (GCMs) over the ice sheets is severely limited by the relatively low resolution of the models at the margins, where surface slopes are greatest. To provide accurate energy-budget estimates, resolutions of better than 0.5° are desirable, requiring nested or multiple gridding and accurate, high-resolution boundary conditions. Here we present a new, high-resolution (5 km) digital elevation model for the Antarctic ice sheet, derived from radar-altimeter data obtained from the geodetic phase of the satellite, ERS-1. These data have been combined with the revised ice-thickness grid reported in Bamber and Huybrechts (1996) to produce a bed- and surface-elevation dataset for use in regional and global climate and paleo-climaie modelling applications. The real level of spatial detail in the datasets has been examined with the aid of Landsat Thematic Mapper data. Imagery around Ice Stream D, West Antarctica, shows that the revised ice-thickness grid is accurately geolocated, and contains valuable fine-scale topographic detail beyond that available from the cartographic version of the data (Drewry, 1983). The surface topography in the region of the Ross Ice Shelf has been used to illustrate the level of detail in both the vertical and horizontal resolution of (he surface dataset. Laudsat data has also been used to examine features in the surface-elevation data. In particular, the location of the grounding zone, for Ice Streams D and E, derived from the two data sources shows good agreement. The results of this validation underscore the utility of the new datasets for high-resolution modelling, and highlight the limitations of the Folio maps for such applications.

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