Abstract:ABSTRACT. We present a new method for extracting the direction of surface flow for ice sheets, based on the detection of flow-induced features that are visible in satellite imagery. The orientation of linear features is determined using a Radon transform and only requires a single image. The technique is demonstrated by applying it to the RADARSAT mosaic of Antarctica, over the Lambert Glacier-Amery Ice Shelf region of East Antarctica. Comparisons with both existing flow-direction fields and traced streamlines… Show more
“…The Radon transform has been demonstrated to be efficient in detecting along-flow features (Roberts et al, 2013), but can also be used for complex flow patterns, like the one in Basin 3 which has a wide range of crevasse orientations. The advantages of the Radon transform over other detecting methods are that crevasse patterns can be extracted where edge detectors methods (Bhardwaj et al, 2015;Wesche et al, 2013) would fail, and also that it is more robust than frequency-domain methods (Sangwine and Thornton, 1998) in detecting crevasses from incomplete coverage due to clouds, image borders or the calving front.…”
Section: Crevasse Mapmentioning
confidence: 99%
“…In this study we followed a similar approach to Roberts et al (2013), but used a more robust implementation and a different post-processing procedure. Firstly, the satellite image was pre-processed with a Laplacian filter to prioritise the high frequencies, e.g.…”
Abstract. The marine-terminating outlet in Basin 3, Austfonna ice cap, has been
accelerating since the mid-1990s. Stepwise multi-annual acceleration
associated with seasonal summer speed-up events was observed before the
outlet entered the basin-wide surge in autumn 2012. We used multiple
numerical models to explore hydrologic activation mechanisms for the surge
behaviour. A continuum ice dynamic model was used to invert basal friction
coefficient distributions using the control method and observed surface
velocity data between April 2012 and July 2014. This has provided input to
a discrete element model capable of simulating individual crevasses, with the
aim of finding locations where meltwater entered the glacier during the summer and
reached the bed. The possible flow paths of surface meltwater reaching the
glacier bed as well as those of meltwater produced at the bed were calculated
according to the gradient of the hydraulic potential. The inverted friction coefficients show the “unplugging” of the stagnant ice
front and expansion of low-friction regions before the surge reached its
peak velocity in January 2013. Crevasse distribution reflects
the basal friction pattern to a high
degree. The meltwater reaches the bed through
the crevasses located above the margins of the subglacial valley and the
basal melt that is generated mainly by frictional heating flows either to
the fast-flowing units or potentially accumulates in an overdeepened
region. Based on these results, the mechanisms facilitated by basal meltwater
production, crevasse opening and the routing of meltwater to the bed are discussed for the surge in
Basin 3.
“…The Radon transform has been demonstrated to be efficient in detecting along-flow features (Roberts et al, 2013), but can also be used for complex flow patterns, like the one in Basin 3 which has a wide range of crevasse orientations. The advantages of the Radon transform over other detecting methods are that crevasse patterns can be extracted where edge detectors methods (Bhardwaj et al, 2015;Wesche et al, 2013) would fail, and also that it is more robust than frequency-domain methods (Sangwine and Thornton, 1998) in detecting crevasses from incomplete coverage due to clouds, image borders or the calving front.…”
Section: Crevasse Mapmentioning
confidence: 99%
“…In this study we followed a similar approach to Roberts et al (2013), but used a more robust implementation and a different post-processing procedure. Firstly, the satellite image was pre-processed with a Laplacian filter to prioritise the high frequencies, e.g.…”
Abstract. The marine-terminating outlet in Basin 3, Austfonna ice cap, has been
accelerating since the mid-1990s. Stepwise multi-annual acceleration
associated with seasonal summer speed-up events was observed before the
outlet entered the basin-wide surge in autumn 2012. We used multiple
numerical models to explore hydrologic activation mechanisms for the surge
behaviour. A continuum ice dynamic model was used to invert basal friction
coefficient distributions using the control method and observed surface
velocity data between April 2012 and July 2014. This has provided input to
a discrete element model capable of simulating individual crevasses, with the
aim of finding locations where meltwater entered the glacier during the summer and
reached the bed. The possible flow paths of surface meltwater reaching the
glacier bed as well as those of meltwater produced at the bed were calculated
according to the gradient of the hydraulic potential. The inverted friction coefficients show the “unplugging” of the stagnant ice
front and expansion of low-friction regions before the surge reached its
peak velocity in January 2013. Crevasse distribution reflects
the basal friction pattern to a high
degree. The meltwater reaches the bed through
the crevasses located above the margins of the subglacial valley and the
basal melt that is generated mainly by frictional heating flows either to
the fast-flowing units or potentially accumulates in an overdeepened
region. Based on these results, the mechanisms facilitated by basal meltwater
production, crevasse opening and the routing of meltwater to the bed are discussed for the surge in
Basin 3.
“…Specifically, we compare radar features between upstream and downstream radar profiles over the Whillans central sticky spot to place observational constraints on flow history. By considering englacial layers, deformation can be inferred throughout the ice column, compared to only observing streaklines at the surface (Fahnestock and others, 2000; Hulbe and Fahnestock, 2007; Glasser and Gudmundsson, 2012; Roberts and others, 2013). Fig.…”
Fast ice flow on the Antarctic continent constitutes much of the mass loss from the ice sheet. However, geophysical methods struggle to constrain ice flow history at depth, or separate the signatures of topography, ice dynamics and basal conditions on layer structure. We develop and demonstrate a methodology to compare layer signatures in multiple airborne radar transects in order to characterize ice flow at depth, or improve coverage of existing radar surveys. We apply this technique to generate synthetic, along-flow radargrams and compare different deformation regimes to observed radargram structure. Specifically, we investigate flow around the central sticky spot of Whillans Ice Stream, West Antarctica. Our study suggests that present-day velocity flowlines are insufficient to characterize flow at depth as expressed in layer geometry, and streaklines provide a better characterization of flow around a basal sticky spot. For Whillans Ice Stream, this suggests that ice flow wraps around the central sticky spot, supported by idealized flow simulations. While tracking isochrone translation and rotation across survey lines is complex, we demonstrate that our approach to combine radargram interpretation and modeling can reveal critical details of past ice flow.
“…The Radon-transform has been demonstrated to be efficient in detecting along flow features (Roberts et al, 2013), but can also be used for complex flow patterns, like the one in Basin 3 which has a wide range of crevasse orientations. The advantages of the Radon-transform over other detecting methods are that crevasse patterns can be extracted where edge detectors methods 135 (Bhardwaj et al, 2015;Wesche et al, 2013) would fail, and also that it is more robust than frequency-domain methods (Sangwine and Thornton, 1998) in detecting crevasses from incomplete coverage due to cloud coverage, image borders or the calving front.…”
mentioning
confidence: 99%
“…In this study we followed a similar approach as Roberts et al (2013), but used a more robust implementation and a different post-processing procedure. Firstly, the satellite image was pre-processed with a Laplacian-filter to prioritize the high 140 frequencies, e.g.…”
Abstract. The marine-terminating outlet in Basin 3, Austfonna ice-cap has been accelerating since the mid-1990s.Step-wise multiannual acceleration associated with seasonal summer speed-up events was observed before the outlet enters the basinwide surge in autumn 2012. We use multiple numerical models to explore hydrologic activation mechanisms for the surge behavior. A continuum ice dynamic model is used to invert basal friction coefficient distributions using the control method and observed surface velocity data between April 2012 and July 2014. This provides an input to a discrete element model The inverted friction coefficients show the 'unplugging' of the stagnant ice front and expansion of low friction regions before the surge reaches its peak velocity in January 2013. Crevasse distribution reflects to a high degree the basal friction pattern.
20The melt water reaches the bed through the crevasses located above the margins of the sub-glacial valley and the basal melt that is generated mainly by frictional heating flows either to the fast flowing units or potentially gets accumulated in an overdeepened region. Based on these results, the mechanisms facilitated by basal melt water production, surface melt water and crevasse opening, for the surge in Basin 3 are discussed.
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