scholarly journals Glaciological observations of Brúarjökull, Iceland, using synthetic aperture radar and thematic mapper satellite data

1995 ◽  
Vol 21 ◽  
pp. 271-276 ◽  
Author(s):  
Dorothy K. Hall ◽  
Richard S. Williams ◽  
Oddur Sigurdsson
Keyword(s):  
Synthetic Aperture Radar ◽  
Thematic Mapper ◽  
Synthetic Aperture ◽  
Glacier Surface ◽  
Outlet Glacier ◽  
Near Surface ◽  
Ice Cap ◽  
Scatter Coefficient ◽  
History Of ◽  
Aperture Radar

The first European Remote Sensing Satellite (ERS-1) synthetic aperture radar (SAR) images offer opportunities for studying glacier surface properties and near-surface features. Analysis of back-scatter values from digital SAR data from 18 January, 7 June, 1 September and 25 October 1993 of Brúarjökull, an outlet glacier on the northeastern margin of the Vatnajökull ice cap, Iceland, that has a history of episodic surges, reveals several back-scatter boundaries that may relate to glacier facies and, inferentially, to mass balance. For example, a strong back-scatter boundary on the 18 January image of the snow-covered glacier, representing a back-scatter coefficient, σ°, difference of 4.34dB, appears to coincide with the position of the transient snow line at the end of the 1990–91 budget year. The boundary is visible on the 7 September 1991 Landsat thematic mapper (TM) image. The terminus is very difficult to define because of back-wasting from the last surge (1963–64) but is most easily delineated on the 1 September 1993 SAR and the 7 September 1991 TM images, in part due to the presence of ice-margin lakes.

scholarly journals Glaciological observations of Brúarjökull, Iceland, using synthetic aperture radar and thematic mapper satellite data

1995 ◽  
Vol 21 ◽  
pp. 271-276 ◽  
Author(s):  
Dorothy K. Hall ◽  
Richard S. Williams ◽  
Oddur Sigurdsson
Keyword(s):  
Synthetic Aperture Radar ◽  
Thematic Mapper ◽  
Synthetic Aperture ◽  
Glacier Surface ◽  
Outlet Glacier ◽  
Near Surface ◽  
Ice Cap ◽  
Scatter Coefficient ◽  
History Of ◽  
Aperture Radar

The first European Remote Sensing Satellite (ERS-1) synthetic aperture radar (SAR) images offer opportunities for studying glacier surface properties and near-surface features. Analysis of back-scatter values from digital SAR data from 18 January, 7 June, 1 September and 25 October 1993 of Brúarjökull, an outlet glacier on the northeastern margin of the Vatnajökull ice cap, Iceland, that has a history of episodic surges, reveals several back-scatter boundaries that may relate to glacier facies and, inferentially, to mass balance. For example, a strong back-scatter boundary on the 18 January image of the snow-covered glacier, representing a back-scatter coefficient, σ°, difference of 4.34dB, appears to coincide with the position of the transient snow line at the end of the 1990–91 budget year. The boundary is visible on the 7 September 1991 Landsat thematic mapper (TM) image. The terminus is very difficult to define because of back-wasting from the last surge (1963–64) but is most easily delineated on the 1 September 1993 SAR and the 7 September 1991 TM images, in part due to the presence of ice-margin lakes.

scholarly journals Early melt season velocity fields of Langjökull and Hofsjökull, central Iceland

2015 ◽  
Vol 61 (226) ◽  
pp. 253-266 ◽  
Author(s):  
Brent Minchew ◽  
Mark Simons ◽  
Scott Hensley ◽  
Helgi Björnsson ◽  
Finnur Pálsson
Keyword(s):  
Synthetic Aperture Radar ◽  
Viscous Flow ◽  
Flow Model ◽  
Vertical Component ◽  
Velocity Fields ◽  
Surface Velocity ◽  
Synthetic Aperture ◽  
Glacier Surface ◽  
Outlet Glacier ◽  
Aperture Radar

AbstractWe infer the horizontal velocity fields of the ice caps Langjökull and Hofsjökull, central Iceland, using repeat-pass interferometric synthetic aperture radar (InSAR). NASA’s uninhabited aerial vehicle synthetic aperture radar (UAVSAR) acquired airborne InSAR data from multiple vantage points during the early melt season in June 2012. We develop a Bayesian approach for inferring three-dimensional velocity fields from multiple InSAR acquisitions. The horizontal components generally agree with available GPS measurements wherever ice motion is well constrained by InSAR observations. We provide evidence that changes in volumetric moisture content near the glacier surface induce phase offsets that obfuscate the vertical component of the surface velocity fields, an effect that could manifest itself on any glacier that experiences surface melt. Spatial patterns in the InSAR-derived horizontal speeds are broadly consistent with the results of a simple viscous flow model, and the directionality of the InSAR-derived horizontal flow field is nearly everywhere consistent with the ice surface gradient. Significant differences between the InSAR-derived horizontal speed and the speed predicted by the viscous flow model suggest that basal slip accounts for more than half the observed outlet glacier flow.

scholarly journals A Synthetic Aperture Radar–Based Climatology of Open-Cell Convection over the Northeast Pacific Ocean

2011 ◽  
Vol 50 (3) ◽  
pp. 594-603 ◽  
Author(s):  
Todd D. Sikora ◽  
George S. Young ◽  
Caren M. Fisher ◽  
Matthew D. Stepp
Keyword(s):  
Pacific Ocean ◽  
Synthetic Aperture Radar ◽  
Vertical Wind Shear ◽  
Heat Fluxes ◽  
Synthetic Aperture ◽  
Cold Pool ◽  
Near Surface ◽  
Open Cell ◽  
Northeastern Pacific ◽  
Aperture Radar

Abstract This paper presents an 8-yr (1999–2006) climatology of the frequency of open-cell convection over the northeastern Pacific Ocean and the thermodynamic and kinematic environment associated with its development. The climatology is based on synthetic aperture radar–derived wind speed images and reanalysis data. The climatology shows that open-cell convection was a cold-season phenomenon, having occurred in environments in which the difference in temperature between the near-surface air and the sea surface is negative and in environments with positive surface sensible and latent heat fluxes. Within the region between the surface and 500 hPa, the 700–850-hPa layer median static stability was near moist adiabatic while that for the remainder was conditionally unstable. The median magnitude of the vertical wind shear was largest in the 925-hPa–near-surface and 500–700-hPa layers while that at midlevels was relatively weak. Similarities are highlighted between the organization of open-cell convection over the northeastern Pacific Ocean and tropical deep moist maritime convection in terms of cold-pool dynamics. Avenues for future work are discussed.

scholarly journals Identification and characterization of alpine subglacial lakes using interferometric synthetic aperture radar (InSAR): Brady Glacier, Alaska, USA

2010 ◽  
Vol 56 (199) ◽  
pp. 861-870 ◽  
Author(s):  
Denny M. Capps ◽  
Bernhard Rabus ◽  
John J. Clague ◽  
Daniel H. Shugar
Keyword(s):  
Synthetic Aperture Radar ◽  
Vertical Displacement ◽  
Synthetic Aperture ◽  
Interferometric Synthetic Aperture Radar ◽  
Glacier Surface ◽  
Discharge Rates ◽  
Outburst Floods ◽  
Glacier Dynamics ◽  
Subglacial Lakes ◽  
Aperture Radar

AbstractThe temporary storage and subsequent release of water at glacial margins can cause severe flooding in downstream areas and substantially impact glacier dynamics. Alpine subglacial lakes may not be identified until they become subaerially exposed or release a jokulhlaup. We use interferometric synthetic aperture radar (InSAR) to identify and characterize three dynamic alpine subglacial lakes of Brady Glacier, Alaska, USA. We quantify changes in vertical displacement of the glacier surface and lake volumes from September 1995 through March 1996 using European Remote-sensing Satellite-1/-2 (ERS- 1/-2) tandem data. In the autumn, subsidence ranged from 4 to 26cmd-1 and the volume of water discharged ranged from 22 000 ± 2000 to 243 000 ± 14 000m3d-1. Subsidence and discharge rates declined significantly during the winter and continued at a lesser rate through March. Application of this technique may allow researchers to locate alpine subglacial lakes years or decades before they begin to release hazardous outburst floods and substantially impact glacier dynamics.

scholarly journals Imaging Subglacial Topography by a Synthetic Aperture Radar Technique

1987 ◽  
Vol 9 ◽  
pp. 170-175 ◽  
Author(s):  
G.J. Musil ◽  
C.S.M. Doake
Keyword(s):  
Synthetic Aperture Radar ◽  
Correlation Method ◽  
Synthetic Aperture ◽  
Scatter Coefficient ◽  
Line Region ◽  
Significant Difference ◽  
Grounding Line ◽  
Subglacial Topography ◽  
Along Track ◽  
Aperture Radar

A synthetic aperture radar (SAR) technique has been used to image part of the grounding-line region of Bach Ice Shelf in the Antarctic Peninsula. The radar was sledge-mounted and operated in a pulsed mode with a carrier frequency of 120 MHz. The coherently detected output was recorded photographically as in-phase and quadrature components. Because the system was essentially stationary for each measurement, there was no doppler information about the reflecting points as in the more commonly used airborne and satellite-based SARs. Instead, the phase history was used directly to identify point targets by a correlation method. Three sounding runs were carried out over the grounding line to give views of the area from separate directions. An aperture length of 104 m was necessary to achieve 8 m resolution in the along-track direction for an ice thickness of 290 m. The mapped swath was 88 m wide. Corrections to the data were made to allow for density variations and absorption in the ice. The back-scatter coefficient showed greater variations in echo strength over grounded ice compared with floating ice and texture analysis of the radar image revealed a statistically significant difference between these two regimes.

scholarly journals Glaciological advances made with interferometric synthetic aperture radar

2010 ◽  
Vol 56 (200) ◽  
pp. 1026-1042 ◽  
Author(s):  
Ian Joughin ◽  
Ben E. Smith ◽  
Waleed Abdalati
Keyword(s):  
Synthetic Aperture Radar ◽  
Flow Velocity ◽  
Synthetic Aperture ◽  
Interferometric Synthetic Aperture Radar ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Mountain Glaciers ◽  
Ice Stream ◽  
Aperture Radar

AbstractSpaceborne interferometric synthetic aperture radar (InSAR) techniques for measuring ice flow velocity and topography have developed rapidly over the last decade and a half, revolutionizing the study of ice dynamics. Spaceborne interferometry has contributed to major progress in many areas of glaciological study by: providing the first comprehensive measurements of ice-stream flow velocity over the major outlets of Greenland and Antarctica; revealing that ice-stream and outlet-glacier flow can change rapidly (months to years); improving understanding of several ice-sheet and ice-shelf processes; providing velocity for flux-gate based mass-balance assessment; mapping flow of mountain glaciers; and capturing the geomorphic traces of past ice flow. We review the basic technique development, the measurement characteristics, and the extensive set of results yielded by these measurements.

scholarly journals Analyses of a surging outlet glacier of Vatnajökull ice cap, Iceland

2005 ◽  
Vol 42 ◽  
pp. 23-28 ◽  
Author(s):  
Guðfinna Aðalgeirsdóttir ◽  
Helgi Björnsson ◽  
Finnur Pálsson ◽  
Eyjolfur Magnússon
Keyword(s):  
Mass Balance ◽  
Glacier Surface ◽  
Measured Velocity ◽  
Outlet Glacier ◽  
Ice Cap ◽  
Elevation Changes ◽  
History Of ◽  
Northern Side ◽  
The Difference ◽  
Approximation Type

AbstractMany of the large outlet glaciers of Vatnajökull ice cap, Iceland, have a history of regular surges. The mass transport during surges can be up to 25% of the total ice flux. This is a considerable amount that affects the whole ice cap, the location of the ice divides, the flow field and the size and shape of the ice cap. Data from the surging outlet Dyngjujökull, on the northern side of Vatnajökull, which surged during the period 1998-2000, are presented: surface elevation changes, displacement and total mass tr ansport. The total gain in ice volume in the receiving area, due to the surge, is considerably smaller than the loss in the reservoir area. The difference is mainly due to enhanced melting rates on the larger surface area of the crevassed glacier surface, and increased turbulent fluxes above the surface, but also due to increased frictional melting at the bed during the surge. A two-dimensional vertically integrated numerical flow model, of standard shallow-ice approximation type, is used to show that a modeled glacier that is similar in size to Dyngjujökull and subject to the same mass balance has three times higher velocities than the measured velocity during the quiescent phase. Adding surges in the numerical model, by periodically increasing the sliding velocity, causes the glacier to retreat and oscillate around a smaller state when subject to the same mass-balance regime. Lowering the equilibrium line by 50 m lets the modeled surging glacier oscillate around a size similar to that of the present glacier, indicating that surging is an efficient long-term ablation mechanism.

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