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.

Glacier displacement on Comfortlessbreen, Svalbard, using 2-pass differential SAR interferometry (DInSAR) with a digital elevation model

Polar Record ◽  
2011 ◽  
Vol 48 (1) ◽  
pp. 17-25 ◽  
Author(s):  
Nora Jennifer Schneevoigt ◽  
Monica Sund ◽  
Wiley Bogren ◽  
Andreas Kääb ◽  
Dan Johan Weydahl
Keyword(s):  
Synthetic Aperture Radar ◽  
Digital Elevation Model ◽  
Sar Interferometry ◽  
Synthetic Aperture ◽  
Synthetic Aperture Radar Interferometry ◽  
Glacier Terminus ◽  
Digital Elevation ◽  
Reference Images ◽  
Elevation Model ◽  
Aperture Radar

ABSTRACTDifferential synthetic aperture radar interferometry (DInSAR) exploits the coherence between the phases of two or more satellite synthetic aperture radar (SAR) scenes taken from the same orbit to separate the phase contributions from topography and movement by subtracting either phase. Hence pure terrain displacement can be derived without residual height information in it, but only the component of movement in line-of-sight direction is represented in a differential interferogram. Comfortlessbreen, a recently surging glacier, flows predominantly in this direction with respect to the European Remote Sensing satellites ERS-1 and ERS-2. Four C-band SAR scenes from spring 1996 were selected because of the high coherence between the respective pairs of the 1-day repeat-pass tandem mission of the ERS sensors. 2-pass DInSAR is performed in combination with a SPOT5 (Satéllite pour l'Observation de la Terre 5) SPIRIT (SPOT5 stereoscopic survey of Polar Ice: Reference Images and Topography) digital elevation model (DEM) from 2007. The different processing steps and intermediate image products, including unwrapping and generation of displacement maps, are detailed in order to convey the DInSAR processing chain to the beginner in the field of interferometry. Maximum horizontal displacements of 18 to 20 cm d−1 in ground range direction can be detected at the glacier terminus, while a few centimetres per day characterised most of the middle and upper portions of Comfortlessbreen in spring 1996.

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 Forest mapping and monitoring with interferometric synthetic aperture radar (InSAR)

2001 ◽  
Vol 25 (2) ◽  
pp. 159-177 ◽  
Author(s):  
H. Balzter
Keyword(s):  
Synthetic Aperture Radar ◽  
Electromagnetic Waves ◽  
Forest Canopy ◽  
Thermal State ◽  
Time Lag ◽  
Sar Interferometry ◽  
Synthetic Aperture ◽  
Dimensional Structure ◽  
Forest Mapping ◽  
Aperture Radar

A synthetic aperture radar (SAR) is an active sensor transmitting pulses of polarized electromagnetic waves and receiving the backscattered radiation. SAR sensors at different wavelengths and with different polarimetric capabilities are being used in remote sensing of the earth. The value of an analysis of backscattered energy alone is limited due to ambiguities in the possible ecological factor configurations causing the signal. From two SAR images taken from similar viewing positions with a short time-lag, interference between the two waves can be observed. By subtracting the two phases of the signals, it is feasible to eliminate the random contribution of the scatterers to the phase. The interferometric correlation and the interferometric phase contain additional information on the three-dimensional structure of the scattering elements in the imaged area. A brief review of SAR sensors is given, followed by an outline of the physical foundations of SAR interferometry and the practical data-processing steps involved. An overview of applications of InSAR to forest mapping and monitoring is given, covering tree-bole volume and biomass, forest types and land cover, fire scars, forest thermal state and forest canopy height.

Transient active deformation in Tainan tableland using persistent scatterers SAR interferometry

2013 ◽  
Vol 184 (4-5) ◽  
pp. 441-450 ◽  
Author(s):  
Yu-Yia Wu ◽  
Jyr-Ching Hu ◽  
Geng-Pei Lin ◽  
Chung-Pai Chang ◽  
Hsin Tung ◽  
...  
Keyword(s):  
Synthetic Aperture Radar ◽  
Surface Deformation ◽  
Sar Interferometry ◽  
Synthetic Aperture ◽  
Uplift Rate ◽  
Active Deformation ◽  
Radar Images ◽  
Persistent Scatterers ◽  
Area North ◽  
Aperture Radar

Abstract Persistent scatterers SAR interferometry (PS-InSAR) was employed to monitor surface deformation in and around the Tainan tableland using 20 advanced synthetic aperture radar (ASAR) images from the ENVISAT satellite taken during the period from 2005 May 19 to 2008 September 25. In our study, we have found that the uplift rate of the northern Tainan tableland is faster than the southern tableland. The slant range displacement (SRD) rate for the area north along the precise leveling array is about 5 to 10 mm/yr with respect to the western edge of the Tainan tableland, whereas the SRD rate for the area south of the leveling array is about 1 to 5 mm/yr. In addition, the uplifted area extends eastward to the Tawan lowland with a maximum SRD rate of nearly 10 mm/yr, which is almost the same as the rate of the Tainan tableland. Results of this study differ from those suggested in previous researches that employed ERS-1/2 radar images taken from 1996 to 1999 and the differential interferometry synthetic aperture radar (D-InSAR) technique. Our findings indicated that the Tawan lowland no longer subsides with respect to the western edge of the Tainan tableland, and that both northern and southern areas are experiencing uplift.

scholarly journals A rapidly converging initialisation method to simulate the present-day Greenland ice sheet using the GRISLI ice sheet model (version 1.3)

2019 ◽  
Vol 12 (6) ◽  
pp. 2481-2499 ◽  
Author(s):  
Sébastien Le clec'h ◽  
Aurélien Quiquet ◽  
Sylvie Charbit ◽  
Christophe Dumas ◽  
Masa Kageyama ◽  
...  
Keyword(s):  
Root Mean Square ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Thickness ◽  
Strong Impact ◽  
Good Representation ◽  
Mean Square ◽  
Method Performance ◽  
Ice Flow ◽  
Mean Square Errors

Abstract. Providing reliable projections of the ice sheet contribution to future sea-level rise has become one of the main challenges of the ice sheet modelling community. To increase confidence in future projections, a good knowledge of the present-day state of ice flow dynamics, which is critically dependent on basal conditions, is strongly needed. The main difficulty is tied to the scarcity of observations at the ice–bed interface at the scale of the whole ice sheet, resulting in poorly constrained parameterisations in ice sheet models. To circumvent this drawback, inverse modelling approaches can be developed to infer initial conditions for ice sheet models that best reproduce available data. Most often such approaches allow for a good representation of the mean present-day state of the ice sheet but are accompanied with unphysical trends. Here, we present an initialisation method for the Greenland ice sheet using the thermo-mechanical hybrid GRISLI (GRenoble Ice Shelf and Land Ice) ice sheet model. Our approach is based on the adjustment of the basal drag coefficient that relates the sliding velocities at the ice–bed interface to basal shear stress in unfrozen bed areas. This method relies on an iterative process in which the basal drag is periodically adjusted in such a way that the simulated ice thickness matches the observed one. The quality of the method is assessed by computing the root mean square errors in ice thickness changes. Because the method is based on an adjustment of the sliding velocities only, the results are discussed in terms of varying ice flow enhancement factors that control the deformation rates. We show that this factor has a strong impact on the minimisation of ice thickness errors and has to be chosen as a function of the internal thermal state of the ice sheet (e.g. a low enhancement factor for a warm ice sheet). While the method performance slightly increases with the duration of the minimisation procedure, an ice thickness root mean square error (RMSE) of 50.3 m is obtained in only 1320 model years. This highlights a rapid convergence and demonstrates that the method can be used for computationally expensive ice sheet models.

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