scholarly journals Improved processing and calibration of the interferometric mode of the CryoSat radar altimeter allows height measurements of supraglacial lakes in west Greenland

2016 ◽  
Author(s):  
Laurence Gray ◽  
David Burgess ◽  
Luke Copland ◽  
Thorben Dunse ◽  
Kirsty Langley ◽  
...  
Keyword(s):  
Normal Incidence ◽  
Ablation Zone ◽  
Radar Altimeter ◽  
Waveform Data ◽  
West Greenland ◽  
Ice Cap ◽  
Supraglacial Lakes ◽  
Ideal Situation ◽  
Digital Elevation ◽  
Devon Ice Cap

Abstract. We compare geocoded heights derived from the interferometric mode (SARIn) of CryoSat to surface heights from calibration-validation sites on Devon Ice Cap and West Greenland. Comparisons are included for both the heights derived from the first return (the "point-of-closest-approach" or POCA) as well as heights derived from delayed waveform returns ("swath" processing). While swath processed heights are normally less accurate than edited POCA heights, of order 1–5 m instead of order 1–2 m, the increased coverage possible with swath data complements the POCA data and provides useful information for both system calibration and improving digital elevation models (DEMs). We show that the pre-launch interferometric baseline coupled with an additional roll correction (~ 0.0075°), or equivalent phase correction (~ 0.0435 radians), provides an improved calibration of the interferometric SARIn mode. We extend the potential use of SARIn data by showing the influence of surface conditions, especially melt, on the return waveforms, and that it is possible to detect and measure the height of summer supraglacial lakes in West Greenland. A supraglacial lake can provide a strong radar target in the waveform, stronger than the initial POCA return, if viewed at near normal incidence. This provides an ideal situation for swath processing and we demonstrate height accuracies of ~ 0.5 m for two lake sites, one in the accumulation zone and one in the ablation zone, which were measured every year from 2010 or 2011 to 2016. Each year the lake in the ablation zone was viewed in June by ascending passes and then 5.5 days later by descending passes which allows an approximate estimate of the filling rate. The results suggest that CryoSat waveform data and measurements of supraglacial lake height change could complement the use of optical satellite and be helpful as proxy indicators for surface melt around Greenland.

scholarly journals A revised calibration of the interferometric mode of the CryoSat-2 radar altimeter improves ice height and height change measurements in western Greenland

2017 ◽  
Vol 11 (3) ◽  
pp. 1041-1058 ◽  
Author(s):  
Laurence Gray ◽  
David Burgess ◽  
Luke Copland ◽  
Thorben Dunse ◽  
Kirsty Langley ◽  
...  
Keyword(s):  
Normal Incidence ◽  
Ablation Zone ◽  
Radar Altimeter ◽  
Waveform Data ◽  
Ice Cap ◽  
Supraglacial Lakes ◽  
Ideal Situation ◽  
Digital Elevation ◽  
Devon Ice Cap ◽  
Height Change

Abstract. We compare geocoded heights derived from the interferometric mode (SARIn) of CryoSat to surface heights from calibration–validation sites on Devon Ice Cap and western Greenland. Comparisons are included for both the heights derived from the first return (the point-of-closest-approach or POCA) and heights derived from delayed waveform returns (swath processing). While swath-processed heights are normally less precise than edited POCA heights, e.g. standard deviations of  ∼  3 and  ∼  1.5 m respectively for the western Greenland site, the increased coverage possible with swath data complements the POCA data and provides useful information for both system calibration and improving digital elevation models (DEMs). We show that the pre-launch interferometric baseline coupled with an additional roll correction ( ∼  0.0075° ± 0.0025°), or equivalent phase correction ( ∼  0.0435 ± 0.0145 radians), provides an improved calibration of the interferometric SARIn mode. We extend the potential use of SARIn data by showing the influence of surface conditions, especially melt, on the return waveforms and that it is possible to detect and measure the height of summer supraglacial lakes in western Greenland. A supraglacial lake can provide a strong radar target in the waveform, stronger than the initial POCA return, if viewed at near-normal incidence. This provides an ideal situation for swath processing and we demonstrate a height precision of  ∼  0.5 m for two lake sites, one in the accumulation zone and one in the ablation zone, which were measured every year from 2010 or 2011 to 2016. Each year the lake in the ablation zone was viewed in June by ascending passes and then 5.5 days later by descending passes, which allows an approximate estimate of the filling rate. The results suggest that CryoSat waveform data and measurements of supraglacial lake height change could complement the use of optical satellite imagery and be helpful as proxy indicators for surface melt around Greenland.

scholarly journals CryoSat-2 delivers monthly and inter-annual surface elevation change for Arctic ice caps

2015 ◽  
Vol 9 (3) ◽  
pp. 2821-2865 ◽  
Author(s):  
L. Gray ◽  
D. Burgess ◽  
L. Copland ◽  
M. N. Demuth ◽  
T. Dunse ◽  
...  
Keyword(s):  
Snow Accumulation ◽  
Surface Elevation ◽  
Radar Altimeter ◽  
Elevation Change ◽  
Ice Caps ◽  
Ice Cap ◽  
Winter Snow ◽  
Surface Elevation Change ◽  
Devon Ice Cap ◽  
Arctic Ice

Abstract. We show that the CryoSat-2 radar altimeter can provide useful estimates of surface elevation change on a variety of Arctic ice caps, on both monthly and yearly time scales. Changing conditions, however, can lead to a varying bias between the elevation estimated from the radar altimeter and the physical surface due to changes in the contribution of subsurface to surface backscatter. Under melting conditions the radar returns are predominantly from the surface so that if surface melt is extensive across the ice cap estimates of summer elevation loss can be made with the frequent coverage provided by CryoSat-2. For example, the average summer elevation decreases on the Barnes Ice Cap, Baffin Island, Canada were 2.05 ± 0.36 m (2011), 2.55 ± 0.32 m (2012), 1.38 ± 0.40 m (2013) and 1.44 ± 0.37 m (2014), losses which were not balanced by the winter snow accumulation. As winter-to-winter conditions were similar, the net elevation losses were 1.0 ± 0.2 m (winter 2010/2011 to winter 2011/2012), 1.39 ± 0.2 m (2011/2012 to 2012/2013) and 0.36 ± 0.2 m (2012/2013 to 2013/2014); for a total surface elevation loss of 2.75 ± 0.2 m over this 3 year period. In contrast, the uncertainty in height change results from Devon Ice Cap, Canada, and Austfonna, Svalbard, can be up to twice as large because of the presence of firn and the possibility of a varying bias between the true surface and the detected elevation due to changing year-to-year conditions. Nevertheless, the surface elevation change estimates from CryoSat for both ice caps are consistent with field and meteorological measurements. For example, the average 3 year elevation difference for footprints within 100 m of a repeated surface GPS track on Austfonna differed from the GPS change by 0.18 m.

scholarly journals Interferometric swath processing of Cryosat data for glacial ice topography

2013 ◽  
Vol 7 (6) ◽  
pp. 1857-1867 ◽  
Author(s):  
L. Gray ◽  
D. Burgess ◽  
L. Copland ◽  
R. Cullen ◽  
N. Galin ◽  
...  
Keyword(s):  
European Space Agency ◽  
Main Beam ◽  
Synthetic Aperture Radar Interferometry ◽  
Ice Cap ◽  
Space Agency ◽  
Digital Elevation ◽  
Interferometric Phase ◽  
Elevation Data ◽  
Devon Ice Cap ◽  
Cross Track

Abstract. We have derived digital elevation models (DEMs) over the western part of the Devon Ice Cap in Nunavut, Canada, using "swath processing" of interferometric data collected by Cryosat between February 2011 and January 2012. With the standard ESA (European Space Agency) SARIn (synthetic aperture radar interferometry) level 2 (L2) data product, the interferometric mode is used to map the cross-track position and elevation of the "point-of-closest-approach" (POCA) in sloping glacial terrain. However, in this work we explore the extent to which the phase of the returns in the intermediate L1b product can also be used to map the heights of time-delayed footprints beyond the POCA. We show that there is a range of average cross-track slopes (~ 0.5 to ~ 2°) for which the returns will be dominated by those beneath the satellite in the main beam of the antenna so that the resulting interferometric phase allows mapping of heights in the delayed range window beyond the POCA. In this way a swath of elevation data is mapped, allowing the creation of DEMs from a sequence of L1b SARIn Cryosat data takes. Comparison of the Devon results with airborne scanning laser data showed a mean difference of order 1 m with a standard deviation of about 1 m. The limitations of swath processing, which generates almost 2 orders of magnitude more data than traditional radar altimetry, are explored through simulation, and the strengths and weaknesses of the technique are discussed.

scholarly journals Digital elevation models for the Lambert Glacier–Amery Ice Shelf system, East Antarctica, from ERS-1 satellite radar altimetry

2000 ◽  
Vol 46 (155) ◽  
pp. 553-560 ◽  
Author(s):  
Helen A. Fricker ◽  
Glenn Hyland ◽  
Richard Coleman ◽  
Neal W. Young
Keyword(s):  
Digital Elevation Models ◽  
Radar Altimeter ◽  
Ice Shelf ◽  
Waveform Data ◽  
Amery Ice Shelf ◽  
Digital Elevation ◽  
Satellite Radar ◽  
Lambert Glacier ◽  
Satellite Radar Altimetry ◽  
Insight Into

AbstractThe Lambert Glacier–Amery Ice Shelf system is a major component of the East Antarctic ice sheet. This paper presents two digital elevation models (DEMs) that have been generated for the Lambert–Amery system from validated European Remote-sensing Satellite (ERS-1) radar altimeter waveform data. The first DEM covers the Amery Ice Shelf only, and was produced using kriging on a 1 km grid. The second is a coarser (5 km) DEM of the entire Lambert–Amery system, generated via simple averaging procedures. The DEMs provide unprecedented surface elevation information for the Lambert–Amery system and allow new insight into the glaciology of the region.

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 Interferometric discrimination of cross-track bed clutter in ice-penetrating radar sounding data

2020 ◽  
Vol 61 (81) ◽  
pp. 68-73 ◽  
Author(s):  
Kirk M. Scanlan ◽  
Anja Rutishauser ◽  
Duncan A. Young ◽  
Donald D. Blankenship
Keyword(s):  
Center Frequency ◽  
Adjacent Area ◽  
Bed Topography ◽  
Ice Cap ◽  
Digital Elevation ◽  
Interferometric Phase ◽  
Devon Ice Cap ◽  
Track Surface ◽  
Cross Track ◽  
Climate Studies

AbstractThe interpretations of relevant interfaces (i.e. the surface and bed) in radar sounding datasets over glaciers and ice sheets are primary boundary conditions in a variety of climate studies and particularly subglacial water routing models. It is therefore necessary to ensure these interpretations are consistent and not affected by cross-track clutter. For the surface interface, interferometry and a family of methods relying on digital elevation models have been used to successfully discriminate cross-track surface clutter. Here we present how interferometry can be applied to the problem of basal clutter from cross-track bed topography. Our approach is based on a comparison of the differential phases of ambiguous reflectors that may represent bed clutter and the differential phase of a reflector in an adjacent area that appears unaffected by basal clutter. The reflector yielding the smallest interferometric phase difference relative to the unambiguous bed reflector is considered to represent its consistent continuation. We successfully demonstrate our approach using 60 MHz center frequency MARFA data collected over Devon Ice Cap in the Canadian Arctic. Finally, we investigate the effects of clutter-affected and interferometry-corrected bed interpretations on ice layer thickness estimates, basal hydraulic head gradients and the potential extent of inferred subglacial water bodies.

scholarly journals CryoSat-2 delivers monthly and inter-annual surface elevation change for Arctic ice caps

2015 ◽  
Vol 9 (5) ◽  
pp. 1895-1913 ◽  
Author(s):  
L. Gray ◽  
D. Burgess ◽  
L. Copland ◽  
M. N. Demuth ◽  
T. Dunse ◽  
...  
Keyword(s):  
Snow Accumulation ◽  
Surface Elevation ◽  
Radar Altimeter ◽  
Elevation Change ◽  
Ice Caps ◽  
Ice Cap ◽  
Winter Snow ◽  
Surface Elevation Change ◽  
Devon Ice Cap ◽  
Arctic Ice

Abstract. We show that the CryoSat-2 radar altimeter can provide useful estimates of surface elevation change on a variety of Arctic ice caps, on both monthly and yearly timescales. Changing conditions, however, can lead to a varying bias between the elevation estimated from the radar altimeter and the physical surface due to changes in the ratio of subsurface to surface backscatter. Under melting conditions the radar returns are predominantly from the surface so that if surface melt is extensive across the ice cap estimates of summer elevation loss can be made with the frequent coverage provided by CryoSat-2. For example, the average summer elevation decreases on the Barnes Ice Cap, Baffin Island, Canada were 2.05 ± 0.36 m (2011), 2.55 ± 0.32 m (2012), 1.38 ± 0.40 m (2013) and 1.44 ± 0.37 m (2014), losses which were not balanced by the winter snow accumulation. As winter-to-winter conditions were similar, the net elevation losses were 1.0 ± 0.20 m (winter 2010/11 to winter 2011/12), 1.39 ± 0.20 m (2011/12 to 2012/13) and 0.36 ± 0.20 m (2012/13 to 2013/14); for a total surface elevation loss of 2.75 ± 0.20 m over this 3-year period. In contrast, the uncertainty in height change from Devon Ice Cap, Canada, and Austfonna, Svalbard, can be up to twice as large because of the presence of firn and the possibility of a varying bias between the true surface and the detected elevation due to changing year-to-year conditions. Nevertheless, the surface elevation change estimates from CryoSat for both ice caps are consistent with field and meteorological measurements.

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 Interferometric swath processing of Cryosat-2 data for glacial ice topography

2013 ◽  
Vol 7 (3) ◽  
pp. 3133-3162 ◽  
Author(s):  
L. Gray ◽  
D. Burgess ◽  
L. Copland ◽  
R. Cullen ◽  
N. Galin ◽  
...  
Keyword(s):  
Digital Elevation Models ◽  
Main Beam ◽  
Glacial Ice ◽  
Ice Cap ◽  
Digital Elevation ◽  
Interferometric Phase ◽  
Elevation Data ◽  
Devon Ice Cap ◽  
Cross Track ◽  
Level 2

Abstract. We have derived Digital Elevation Models (DEMs) over the western part of the Devon Ice Cap in Nunavut Canada using "swath processing" of interferometric data collected by Cryosat 2 between February 2011 and January 2012. In the standard ESA "SARIn" level 2 (L2) data product the interferometric mode is used to map the cross-track position and elevation of the "point-of-closest-approach" (POCA) in sloping glacial terrain. However, in this work we explore the extent to which the phase of the returns in the intermediate L1b product can also be used to map the heights of time delayed footprints beyond the POCA. We show that there is a range of average cross-track slopes (~0.5° to ~2°) for which the returns will be dominated by those beneath the satellite in the main beam of the antenna and that the resulting interferometric phase allows mapping of heights in the delayed range window beyond the POCA. In this way a swath of elevation data is mapped allowing the creation of Digital Elevation Models (DEMs) from a sequence of L1b SARIn Cryosat-2 data takes. Comparison of the Devon results with airborne scanning laser data showed a mean difference of order a meter with a standard deviation < 1 m. The limitations of swath processing, which generates almost 2 orders of magnitude more data than traditional radar altimetry, are explored through simulation, and the strengths and weaknesses of the technique are discussed.

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