Monitoring the Greenland Ice Sheet: A comparison between Sentinel-3 and CryoSat-2 radar altimeters

2020 ◽  
Author(s):  
Jennifer Maddalena ◽  
Geoffrey Dawson ◽  
Stephen Chuter ◽  
Jack Landy ◽  
Jonathan Bamber
Keyword(s):  
Synthetic Aperture Radar ◽  
Volume Change ◽  
Interpolation Method ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Synthetic Aperture ◽  
Radar Altimeter ◽  
Elevation Change ◽  
Crossover Analysis ◽  
Aperture Radar

<p>Since 1992, satellite-borne radar altimetry has been used to record surface elevation change over the Greenland ice sheet (GrIS). Until the launch of CryoSat-2 in 2010, conventional radar altimeters performed poorly over high sloping terrain with heterogenous topography. The novel synthetic aperture radar interferometric (SARIn) mode of CryoSat-2 has improved capability in these regions over the margins of the GrIS, which have been experiencing the largest mass loss. ESA’s Sentinel-3 mission is the latest radar-altimeter to be launched. The first satellite, Sentinel-3A, was launched in February 2016 followed by Sentinel-3B April 2018. The Sentinel-3 satellites are the first to use synthetic aperture radar (SAR) across the interior of the GrIS. This has improved the along-track resolution to approximately 300m compared to CryoSat-2’s Low Resolution Mode (LRM) footprint which has a diameter of ~1.65km.</p><p>Here we assess the performance of Sentinel’s SAR mode compared to the LRM mode of CryoSat-2 over the interior of the ice sheet and the SARIn mode over the margins of the GrIS, through crossover analysis and a point-to-point comparison. We then assess the implications of this comparison for monitoring elevation changes over the ice sheet and we present rates of elevation change for June 2016 - June 2019 for both radar altimeter missions. To calculate rates of volume change from elevation change we use a statistical interpolation method, universal kriging, and present volume changes per basin over Greenland before comparing volume change estimates between CryoSat-2 and Sentinel-3.</p>

scholarly journals Analysis of synthetic aperture radar Data collected over the southwestern Greenland ice sheet

1993 ◽  
Vol 39 (131) ◽  
pp. 119-132 ◽  
Author(s):  
K. C. Jezek ◽  
M. R. Drinkwater ◽  
J. P. Crawford ◽  
R. Bindschadler ◽  
R. Kwok
Keyword(s):  
Synthetic Aperture Radar ◽  
Large Scale ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Synthetic Aperture ◽  
Model Calculations ◽  
Synthetic Aperture Radar Data ◽  
Surface Patterns ◽  
Sar Data ◽  
Aperture Radar

AbstractAnalyses of the first aircraft multi-frequency, Polarimetric synthetic aperture radar (SAR) data acquired over the southwestern Greenland ice sheet are presented. Data were collected on 31 August 1989 by the Jet Propulsion Laboratory SAR using the NASA DC-8 aircraft. Along with curvilinear patterns associated with large-scale morphologic features such as crevasses, lakes and streams, frequency and polarization dependencies are observed in the P-, L-and C-band image products. Model calculations that include firn grain-size and volumetric water content suggest that tonal variations in and between the images are attributable to large-scale variations in the snow-and ice-surface characteristics, especially snow wetness. In particular, systematic trends in back-scatter strength observed at C-band across regions of changing snow wetness are suggestive of a capability to delineate boundaries between snow facies. Ice lenses and ice pipes are the speculated cause for similar trends in P-band back-scatter. Finally, comparison between SEASAT SAR data collected in 1978 and these airborne data collected in 1989 indicate a remarkable stability of surface patterns associated with the locations of supraglacial lake and stream systems.

scholarly journals An analysis of balance velocities over the Greenland ice sheet and comparison with synthetic aperture radar interferometry

2000 ◽  
Vol 46 (152) ◽  
pp. 67-74 ◽  
Author(s):  
J. L. Bamber ◽  
R. J. Hardy ◽  
I. Joughin
Keyword(s):  
Synthetic Aperture Radar ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ablation Rate ◽  
Sar Interferometry ◽  
Synthetic Aperture ◽  
Ice Thickness ◽  
Good Representation ◽  
Elevation Model ◽  
Aperture Radar

AbstractBalance velocities for the Greenland ice sheet have been calculated from a new digital elevation model (DEM), accumulation rates and an existing ice-thickness grid, using a fully two-dimensional finite-difference scheme. The pattern of velocities is compared with velocities derived from synthetic-aperture radar (SAR) interferometry for three different regions of the ice sheet. Differences between the two estimates of velocity highlight the respective strengths and weaknesses of the datasets and techniques used. A comparison with ten global positioning system-derived velocities indicates that the balance-velocity scheme and input datasets used here provide a remarkably good representation of the velocity distribution inland from the margins. These balance-velocity data, therefore, could help constrain numerical ice-sheet models. The balance velocities were found to be unreliable close to the ice-sheet margins due to larger errors in ice thickness, surface slope and ablation rate in this region. Comparison of the balance velocities with SAR interferometry in the region of the “Northeast Greenland Ice Stream” indicates the importance of the smoothing distance that must be applied to the DEM before calculating balance velocities. A smoothing distance of 20 times the ice thickness gave good agreement between the two measures of velocity.

scholarly journals Analysis of synthetic aperture radar Data collected over the southwestern Greenland ice sheet

1993 ◽  
Vol 39 (131) ◽  
pp. 119-132 ◽  
Author(s):  
K. C. Jezek ◽  
M. R. Drinkwater ◽  
J. P. Crawford ◽  
R. Bindschadler ◽  
R. Kwok
Keyword(s):  
Synthetic Aperture Radar ◽  
Large Scale ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Synthetic Aperture ◽  
Model Calculations ◽  
Synthetic Aperture Radar Data ◽  
Surface Patterns ◽  
Sar Data ◽  
Aperture Radar

AbstractAnalyses of the first aircraft multi-frequency, Polarimetric synthetic aperture radar (SAR) data acquired over the southwestern Greenland ice sheet are presented. Data were collected on 31 August 1989 by the Jet Propulsion Laboratory SAR using the NASA DC-8 aircraft. Along with curvilinear patterns associated with large-scale morphologic features such as crevasses, lakes and streams, frequency and polarization dependencies are observed in the P-, L-and C-band image products. Model calculations that include firn grain-size and volumetric water content suggest that tonal variations in and between the images are attributable to large-scale variations in the snow-and ice-surface characteristics, especially snow wetness. In particular, systematic trends in back-scatter strength observed at C-band across regions of changing snow wetness are suggestive of a capability to delineate boundaries between snow facies. Ice lenses and ice pipes are the speculated cause for similar trends in P-band back-scatter. Finally, comparison between SEASAT SAR data collected in 1978 and these airborne data collected in 1989 indicate a remarkable stability of surface patterns associated with the locations of supraglacial lake and stream systems.

scholarly journals Assessment of DUACS Sentinel-3A Altimetry Data in the Coastal Band of the European Seas: Comparison with Tide Gauge Measurements

2020 ◽  
Vol 12 (23) ◽  
pp. 3970
Author(s):  
Antonio Sánchez-Román ◽  
Ananda Pascual ◽  
Marie-Isabelle Pujol ◽  
Guillaume Taburet ◽  
Marta Marcos ◽  
...  
Keyword(s):  
Synthetic Aperture Radar ◽  
Tide Gauge ◽  
Synthetic Aperture ◽  
Altimetry Data ◽  
Radar Altimeter ◽  
Long Wave ◽  
Tide Gauge Measurements ◽  
European Seas ◽  
Aperture Radar

The quality of the Data Unification and Altimeter Combination System (DUACS) Sentinel-3A altimeter data in the coastal area of the European seas is investigated through a comparison with in situ tide gauge measurements. The comparison was also conducted using altimetry data from Jason-3 for inter-comparison purposes. We found that Sentinel-3A improved the root mean square differences (RMSD) by 13% with respect to the Jason-3 mission. In addition, the variance in the differences between the two datasets was reduced by 25%. To explain the improved capture of Sea Level Anomaly by Sentinel-3A in the coastal band, the impact of the measurement noise on the synthetic aperture radar altimeter, the distance to the coast, and Long Wave Error correction applied on altimetry data were checked. The results confirmed that the synthetic aperture radar altimeter instrument onboard the Sentinel-3A mission better solves the signal in the coastal band. Moreover, the Long Wave Error processing contributes to reduce the errors in altimetry, enhancing the consistency between the altimeter and in situ datasets.

scholarly journals A comparison of Greenland ice-sheet volume changes derived from altimetry measurements

2008 ◽  
Vol 54 (185) ◽  
pp. 203-212 ◽  
Author(s):  
Robert Thomas ◽  
Curt Davis ◽  
Earl Frederick ◽  
William Krabill ◽  
Yonghong Li ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Altimeter Data ◽  
Time Interval ◽  
Radar Altimeter ◽  
Elevation Change ◽  
Laser Altimeter ◽  
The North ◽  
Radar Waveforms ◽  
Summer Temperatures

AbstractWe compare rates of surface-elevation change on the Greenland ice sheet derived from European Remote-sensing Satellite-2 (ERS-2) radar-altimeter data with those obtained from laser-altimeter data collected over nearly the same time periods. Radar-altimeter data show more rapid thickening (9 ± 1 cm a−1 above 1500 m elevation in the north, and 3 ± 1 cm a−1 above 2000 m in the south) than the laser estimates, possibly caused by a lifting of the radar-reflection horizon associated with changes in the snowpack, such as those caused by progressively increased surface melting, as summer temperatures rise. Over all the ice sheet above 2000 m, this results in an ERS-derived volume balance ∼75 ± 15 km3 a−1 more positive than that from laser data. This bias between laser and radar estimates of elevation change varies spatially and temporally, so cannot at present be corrected without independent surveys such as those presented here. At lower elevations, comparison of detailed repeat laser surveys over Jakobshavn Isbræ with ERS results over the same time interval shows substantial ERS underestimation of ice-thinning rates. This results partly from missing data because of ‘bad’ radar waveforms over the very rough surface topography, and partly from the tendency for large radar footprints to sample preferentially local high points in the topography, thus missing regions of most rapid thinning along glacier depressions.

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