scholarly journals BedMachine v3: Complete Bed Topography and Ocean Bathymetry Mapping of Greenland From Multibeam Echo Sounding Combined With Mass Conservation

2017 ◽  
Vol 44 (21) ◽  
Author(s):  
M. Morlighem ◽  
C. N. Williams ◽  
E. Rignot ◽  
L. An ◽  
J. E. Arndt ◽  
...  
Keyword(s):  
Mass Conservation ◽  
Bed Topography ◽  
Echo Sounding

scholarly journals Stochastic modeling of subglacial topography exposes uncertainty in water routing at Jakobshavn Glacier

2020 ◽  
pp. 1-9
Author(s):  
Emma J. MacKie ◽  
Dustin M. Schroeder ◽  
Chen Zuo ◽  
Zhen Yin ◽  
Jef Caers
Keyword(s):  
Mass Conservation ◽  
Simulation Method ◽  
Radar Data ◽  
Geostatistical Simulation ◽  
Ice Flow ◽  
Bed Topography ◽  
Drainage Patterns ◽  
Secondary Constraint ◽  
Subglacial Topography ◽  
Data Coverage

Abstract Subglacial topography is an important feature in numerous ice-sheet analyses and can drive the routing of water at the bed. Bed topography is primarily measured with ice-penetrating radar. Significant gaps, however, remain in data coverage that require interpolation. Topographic interpolations are typically made with kriging, as well as with mass conservation, where ice flow dynamics are used to constrain bed geometry. However, these techniques generate bed topography that is unrealistically smooth at small scales, which biases subglacial water flowpath models and makes it difficult to rigorously quantify uncertainty in subglacial drainage patterns. To address this challenge, we adapt a geostatistical simulation method with probabilistic modeling to stochastically simulate bed topography such that the interpolated topography retains the spatial statistics of the ice-penetrating radar data. We use this method to simulate subglacial topography using mass conservation topography as a secondary constraint. We apply a water routing model to each of these realizations. Our results show that many of the flowpaths significantly change with each topographic realization, demonstrating that geostatistical simulation can be useful for assessing confidence in subglacial flowpaths.

Inverting surface-elevation data and velocity for basal topography beneath Thwaites Glacier, West Antarctica

2021 ◽  
Author(s):  
Helen Ockenden ◽  
Andrew Curtis ◽  
Daniel Goldberg ◽  
Antonios Giannopoulos ◽  
Robert Bingham
Keyword(s):  
Perturbation Theory ◽  
Mathematical Formulation ◽  
Mass Conservation ◽  
Momentum Balance ◽  
Linear Perturbation ◽  
Consistent Estimate ◽  
West Antarctica ◽  
Bed Topography ◽  
Ice Surface ◽  
Linear Perturbation Theory

<p>Thwaites Glacier in West Antarctica is one of the regions of the fastest accelerating ice thinning and highest observed ice loss. The topography of the bed beneath the glacier is a key control of future ice loss, but is not currently well enough known to satisfy the requirements of ice sheet models predicting glacier behaviour. It has previously been suggested that in fast flowing ice streams the shapes of landforms at the bed should be reflected in the ice surface morphology, which is known to a much higher resolution. Indeed, recently published radar grids from Pine Island Glacier reveal bed landforms with a definite resemblance to the ice surface above them. Here, we present a new high resolution bed topography map of Thwaites Glacier, inverted from REMA and ITSLIVE data using linear perturbation theory, a mathematical formulation of this resemblance between bed and surface.  As it is based on linear physics, this method is faster than mass conservation and streamline diffusion interpolation, the two main techniques utilised by existing bed topography products in this region. Furthermore, as the theory is based on both mass and momentum balance, it provides a physically consistent estimate of elevation and basal slipperiness, in contrast to these more widely used methods. The resulting bed matches well with existing airborne and swath radar surveys, with significant detail between these radar lines. Variation in the results obtained using different reference models provides a measure of validity of the linear perturbation theory. Due to the importance of form drag in patterns of ice retreat, the inverted topographic features are potentially important for the future behaviour of Thwaites Glacier.</p>

scholarly journals Coherent large beamwidth processing of radio-echo sounding data

2018 ◽  
Vol 12 (9) ◽  
pp. 2969-2979 ◽  
Author(s):  
Anton Heister ◽  
Rolf Scheiber
Keyword(s):  
Ice Sheets ◽  
Internal Layers ◽  
Spectral Filtering ◽  
Polar Ice ◽  
Bed Topography ◽  
Ice Surface ◽  
Radio Echo Sounding ◽  
Polar Ice Sheets ◽  
Slope Estimation ◽  
Echo Sounding

Abstract. Coherent processing of radio-echo sounding data of polar ice sheets is known to provide an indication of bedrock properties and detection of internal layers. We investigate the benefits of coherent processing of a large azimuth beamwidth to retrieve and characterize the orientation and angular backscattering properties of the surface and subsurface features. MCRDS data acquired over two distinct test areas in Greenland are used to demonstrate the specular backscattering properties of the ice surface and of the internal layers, as well as the much wider angular response of the bedrock. The coupling of internal layers' orientation with the bed topography is shown to increase with depth. Spectral filtering can be used to increase the SNR of the internal layers and mitigate the surface multiple. The variance of the bed backscattering can be used to characterize the bed return specularity. The use of the SAR-focused RES data ensures the correct azimuth positioning of the internal layers for the subsequent slope estimation.

scholarly journals Benefits of Coherent Large Beamwidth Processing of Radio-Echo Sounding Data

2018 ◽  
Author(s):  
Anton Heister ◽  
Rolf Scheiber
Keyword(s):  
Ice Sheets ◽  
Internal Layers ◽  
Spectral Filtering ◽  
Polar Ice ◽  
Angular Response ◽  
Bed Topography ◽  
Ice Surface ◽  
Radio Echo Sounding ◽  
Polar Ice Sheets ◽  
Echo Sounding

Abstract. Coherent processing of radio echo sounding data of polar ice sheets is known to provide indication of bedrock properties and detection of internal layers. We investigate the benefits of coherent processing of a large azimuth beamwidth to retrieve and characterize the orientation and angular backscattering properties of the surface and subsurface features. MCoRDS data acquired over two distinct test areas in Greenland are used to demonstrate the specular backscattering properties of the ice surface and of the internal layers, as well as the much wider angular response of the bedrock. The coupling of internal layers' orientation with the bed topography is shown to increase with depth. Spectral filtering can be used to increase the SNR of the internal layers and for mitigating the surface multiple.

scholarly journals Inverting ice surface elevation and velocity for bed topography and slipperiness beneath Thwaites Glacier

2021 ◽  
Author(s):  
Helen Ockenden ◽  
Robert G. Bingham ◽  
Andrew Curtis ◽  
Daniel Goldberg
Keyword(s):  
High Resolution ◽  
Ice Sheets ◽  
Mass Conservation ◽  
Radar Data ◽  
Surface Flow ◽  
Surface Elevation ◽  
Linear Perturbation ◽  
Detailed Knowledge ◽  
Bed Topography ◽  
Ice Stream

Abstract. There is significant uncertainty over how ice sheets and glaciers will respond to rising global temperatures. Limited knowledge of the topography and rheology of ice-bed interface is a key cause of this uncertainty, as models show that small changes in the bed can have a large influence on predicted rates of ice loss. Most of our detailed knowledge of bed topography comes from airborne and ground-penetrating radar observations. However, these direct observations are not spaced closely enough to meet the requirements of ice-sheet models, so interpolation and inversion methods are used to fill in the gaps. Here we present the results of a new inversion of surface-elevation and velocity data over Thwaites Glacier, West Antarctica, for bed topography and slipperiness (i.e. the degree of basal slip for a given level of drag). The inversion is based on a steady-state linear perturbation analysis of the shallow-ice-stream equations. The method works by identifying disturbances to surface flow which are caused by obstacles or sticky patches in the bed, and can therefore be applied wherever the shallow-ice-stream equations hold and where surface data are available, even where the ice thickness is not well known. We assess the performance of the inversion for topography with the available radar data. Although the topographic output from the inversion is less successful where the bed slopes steeply, it compares well with radar data from the central trunk of the glacier. This method could therefore be useful as either an independent test of other interpolation methods such as mass conservation and kriging, or as a complementary technique in regions where those techniques fail. We do not have data to allow us to assess the success of the slipperiness results from our inversions, but we provide maps that may guide future seismic data collection across Thwaites Glacier. The methods presented here show significant promise for using high-resolution satellite datasets, calibrated by the sparser field datasets, to generate high resolution bed topography products across the ice sheets, and therefore contribute to reduced uncertainty in predictions of future sea-level rise.

scholarly journals High-resolution bed topography mapping of Russell Glacier, Greenland, inferred from Operation IceBridge data

2013 ◽  
Vol 59 (218) ◽  
pp. 1015-1023 ◽  
Author(s):  
M. Morlighem ◽  
E. Rignot ◽  
J. Mouginot ◽  
X. Wu ◽  
H. Seroussi ◽  
...  
Keyword(s):  
Mass Conservation ◽  
Radar Data ◽  
Airborne Radar ◽  
Ice Thickness ◽  
Flux Divergence ◽  
Motion Data ◽  
Bed Topography ◽  
Bed Elevation ◽  
Comparable Performance ◽  
Mapping Techniques

AbstractDetailed maps of bed elevation and ice thickness are essential for understanding and projecting the evolution of the ice sheets. Such maps are traditionally obtained using airborne radar-sounding profiler data interpolated onto regular grids using geostatistical tools such as kriging. Here we compare three mapping techniques applied to a dense radar survey of Russell Glacier, West Greenland, by NASA Operation IceBridge: (1) radar tomography (RT) processing of the radar data to map the bed elevation, (2) interpolation of radar-derived thickness by ordinary kriging (KR) and (3) reconstruction of ice thickness based on the principles of mass conservation (MC) combining radar-sounding profiler and ice motion data. RT eliminates ambiguities caused by off-nadir reflections, but is spatially limited. KR yields a standard error in bed elevation of 35 m, but large errors (>300 m a−1) in flux divergence when combined with ice motion data. MC yields a comparable performance in bed elevation mapping, and errors smaller than 1 m a−1 in flux divergence. When the number of radar-sounding tracks is reduced, the performance of KR decreases more rapidly than for MC. Our study site shows that MC is capable of maintaining precision levels of 60 m at 400 m posting with flight tracks separated by 5 km.

Echo-sounding devices

1936 ◽  
Vol 7 (25) ◽  
pp. 13
Author(s):  
J.F.B. Darwin
Keyword(s):  
Echo Sounding
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