scholarly journals An iterative inverse method to estimate basal topography and initialize ice flow models

2013 ◽  
Vol 7 (3) ◽  
pp. 987-1006 ◽  
Author(s):  
W. J. J. van Pelt ◽  
J. Oerlemans ◽  
C. H. Reijmer ◽  
R. Pettersson ◽  
V. A. Pohjola ◽  
...  
Keyword(s):  
Inverse Method ◽  
Thickness Distribution ◽  
Radar Data ◽  
Three Dimensions ◽  
Time Dependent ◽  
Ice Flow ◽  
Flow Models ◽  
Ice Caps ◽  
Inverse Approach ◽  
Bedrock Topography

Abstract. We evaluate an inverse approach to reconstruct distributed bedrock topography and simultaneously initialize an ice flow model. The inverse method involves an iterative procedure in which an ice dynamical model (PISM) is run multiple times over a prescribed period, while being forced with space- and time-dependent climate input. After every iteration bed heights are adjusted using information of the remaining misfit between observed and modeled surface topography. The inverse method is first applied in synthetic experiments with a constant climate forcing to verify convergence and robustness of the approach in three dimensions. In a next step, the inverse approach is applied to Nordenskiöldbreen, Svalbard, forced with height- and time-dependent climate input since 1300 AD. An L-curve stopping criterion is used to prevent overfitting. Validation against radar data reveals a high correlation (up to R = 0.89) between modeled and observed thicknesses. Remaining uncertainties can mainly be ascribed to inaccurate model physics, in particular, uncertainty in the description of sliding. Results demonstrate the applicability of this inverse method to reconstruct the ice thickness distribution of glaciers and ice caps. In addition to reconstructing bedrock topography, the method provides a direct tool to initialize ice flow models for forecasting experiments.

scholarly journals An iterative inverse method to estimate basal topography and initialize ice flow models

2013 ◽  
Vol 7 (2) ◽  
pp. 873-920
Author(s):  
W. J. J. van Pelt ◽  
J. Oerlemans ◽  
C. H. Reijmer ◽  
R. Pettersson ◽  
V. A. Pohjola ◽  
...  
Keyword(s):  
Inverse Method ◽  
Thickness Distribution ◽  
Radar Data ◽  
Time Dependent ◽  
Climate Forcing ◽  
Ice Flow ◽  
Flow Models ◽  
Ice Caps ◽  
Inverse Approach ◽  
Bedrock Topography

Abstract. We present and evaluate an inverse approach to reconstruct two-dimensional fields of bedrock topography and simultaneously initialize an ice flow model. The inverse method involves an iterative procedure in which an ice dynamical model (PISM) is run multiple times over a prescribed period, while being forced with space and time-dependent climate input. After every iteration bed heights are adjusted using information of the remaining misfit between observed and modeled surface topography. The inverse method is first applied in synthetic experiments with a constant climate forcing to verify convergence and robustness of the approach. In a next step, the inverse approach is applied to Nordenskiöldbreen, Svalbard, forced with height- and time-dependent climate input since 1300 AD. An L-curve stopping criterion is used to prevent overfitting. Validation against radar data reveals a high correlation (up to R = 0.89) between modeled and observed thicknesses. Remaining uncertainties can mainly be ascribed to inaccurate model physics, in particular uncertainty in the description of sliding. Results demonstrate the applicability of this inverse method to reconstruct the ice thickness distribution of glaciers and ice caps. In addition to reconstructing bedrock topography, the method provides a direct tool to initialize ice flow models for forecasting experiments. Application of the method is not constrained to a single model or glacier, indicating the potential to use the approach to compute the detailed thickness distribution of a single glacier, as well as the volume contained in a set of glaciers and ice caps.

Constraining ice shelf basalt melting rates from isochrone data

2021 ◽  
Author(s):  
Vjeran Visnjevic ◽  
Reinhard Drews ◽  
Clemens Schannwell ◽  
Inka Koch
Keyword(s):  
Ocean Circulation ◽  
Radar Data ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Ice Shelves ◽  
Inverse Approach ◽  
History Of ◽  
Forward And Inverse Modeling ◽  
Basal Melting

<p>Ice shelves buttress ice flow from the continent towards the ocean, and their disintegration results in increased ice discharge.  Ice-shelf evolution and integrity is influenced by surface accumulation, basal melting, and ice dynamics. We find signals of all of these processes imprinted in the ice-shelf stratigraphy that can be mapped using isochrones imaged with radar.</p><p>Our aim is to develop an inverse approach to infer ice shelf basal melt rates using radar isochrones as observational constraints. Here, we investigate the influence of basalt melt rates on the shape of isochrones using combined insights from both forward and inverse modeling. We use the 3D full Stokes model Elmer/Ice in our forward simulations, aiming to reproduce isochrone patterns observed in our data. Moreover we develop an inverse approach based on the shallow shelf approximating, aiming to constrain basal melt rates using isochronal radar data and surface velocities. Insights obtained from our simulations can also guide the collection of new radar data (e.g., profile lines along vs. across-flow) in a way that ambiguities in interpreting the ice-shelf stratigraphy can be minimized. Eventually, combining these approaches will enable us to better constrain the magnitude and history of basal melting, which will give valuable input for ocean circulation and sea level rise projections.</p>

scholarly journals The ice thickness distribution of Flask Glacier, Antarctic Peninsula, determined by combining radio-echo soundings, surface velocity data and flow modelling

2013 ◽  
Vol 54 (63) ◽  
pp. 18-24 ◽  
Author(s):  
Daniel Farinotti ◽  
Hugh Corr ◽  
G.Hilmar Gudmundsson
Keyword(s):  
Antarctic Peninsula ◽  
Thickness Distribution ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Volume ◽  
Flow Modelling ◽  
Bedrock Topography ◽  
Sparse Measurements

AbstractAn interpolated bedrock topography is presented for Flask Glacier, one of the tributaries of the remnant part of the Larsen B ice shelf, Antarctic Peninsula. The ice thickness distribution is derived by combining direct but sparse measurements from airborne radio-echo soundings with indirect estimates obtained from ice-flow modelling. The ice-flow model is applied to a series of transverse profiles, and a first estimate of the bedrock is iteratively adjusted until agreement between modelled and measured surface velocities is achieved. The adjusted bedrock is then used to reinterpret the radio-echo soundings, and the recovered information used to further improve the estimate of the bedrock itself. The ice flux along the glacier center line provides an additional and independent constraint on the ice thickness. The resulting bedrock topography reveals a glacier bed situated mainly below sea level with sections having retrograde slope. The total ice volume of 120 ±15 km3 for the considered area of 215 km2 corresponds to an average ice thickness of 560 ± 70 m.

scholarly journals The transferability of adjoint inversion products between different ice flow models

2020 ◽  
Author(s):  
Jowan M. Barnes ◽  
Thiago Dias dos Santos ◽  
Daniel Goldberg ◽  
G. Hilmar Gudmundsson ◽  
Mathieu Morlighem ◽  
...  
Keyword(s):  
Thickness Distribution ◽  
West Antarctica ◽  
Amundsen Sea ◽  
Ice Flow ◽  
Flow Models ◽  
Extra Effort ◽  
Direct Observations ◽  
Basal Sliding ◽  
Process Studies ◽  
The Subject

Abstract. Among the most important challenges faced by ice flow models is how to represent basal and rheological conditions, which are challenging to obtain from direct observations. A common practice is to use numerical inversions to calculate estimates for the unknown properties, but there are many possible methods and not one standardised approach. As such, every ice flow model has a unique initialisation procedure. Here we compare the outputs of inversions from three different ice flow models, each employing a variant of adjoint-based optimisation to calculate basal sliding coefficients and flow rate factors using the same observed surface velocities and ice thickness distribution. The region we focus on is the Amundsen Sea Embayment in West Antarctica, the subject of much investigation due to rapid changes in the area over recent decades. We find that our inversions produce similar distributions of basal sliding across all models, despite using different techniques, implying that the methods used are highly robust and represent the physics without much influence by individual model behaviours. Transferring the products of inversions between models results in time-dependent simulations displaying variability on the order of or lower than existing model intercomparisons and process studies. While the successful transfer of inversion outputs from one model to another requires some extra effort and technical knowledge of the particular models involved, it is certainly possible and could indeed be useful for future intercomparison projects.

scholarly journals The bedrock topography of Gries- and Findelengletscher

2018 ◽  
Vol 73 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Nadine Feiger ◽  
Matthias Huss ◽  
Silvan Leinss ◽  
Leo Sold ◽  
Daniel Farinotti
Keyword(s):  
Spatial Interpolation ◽  
Thickness Distribution ◽  
Estimation Method ◽  
Ice Thickness ◽  
Glacier Surface ◽  
Ice Flow ◽  
Bedrock Topography ◽  
Abstract Knowledge ◽  
Ground Penetrating ◽  
Item Item

Abstract. Knowledge of the ice thickness distribution of glaciers is important for glaciological and hydrological applications. In this contribution, we present two updated bedrock topographies and ice thickness distributions for Gries- and Findelengletscher, Switzerland. The results are based on ground-penetrating radar (GPR) measurements collected in spring 2015 and already-existing data. The GPR data are analysed using ReflexW software and interpolated by using the ice thickness estimation method (ITEM). ITEM calculates the thickness distribution by using principles of ice flow dynamics and characteristics of the glacier surface. We show that using such a technique has a significance advantage compared to a direct interpolation of the measurements, especially for glacier areas that are sparsely covered by GPR data. The uncertainties deriving from both the interpretation of the GPR signal and the spatial interpolation through ITEM are quantified separately, showing that, in our case, GPR signal interpretation is a major source of uncertainty. The results show a total glacier volume of 0.28±0.06 and 1.00±0.34 km3 for Gries- and Findelengletscher, respectively, with corresponding average ice thicknesses of 56.8±12.7 and 56.3±19.6 m.

scholarly journals Surface undulations of Antarctic ice streams tightly controlled by bedrock topography

2012 ◽  
Vol 6 (5) ◽  
pp. 4485-4516 ◽  
Author(s):  
J. De Rydt ◽  
G. H. Gudmundsson ◽  
H. F. J. Corr ◽  
P. Christoffersen
Keyword(s):  
Spatial Scales ◽  
Radar Data ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Ice Streams ◽  
Slip Ratio ◽  
Flow Models ◽  
Bedrock Topography ◽  
Ice Stream ◽  
The Mean

Abstract. Full Stokes models predict that fast-flowing ice streams transmit information about their bedrock topography most efficiently to the surface for basal undulations with length scales between 1 and 20 times the mean ice thickness. This typical behaviour is independent on the precise values of the flow law and sliding law exponents, and should be universally observable. However, no experimental evidence for this important theoretical prediction has been obtained so far, hence ignoring an important test for the physical validity of current-day ice flow models. In our work we use recently acquired airborne radar data for the Rutford Ice Stream and Evans Ice Stream, and we show that the surface response of fast-flowing ice is highly sensitive to bedrock irregularities with wavelengths of several ice thicknesses. The sensitivity depends on the slip ratio, i.e. the ratio between mean basal sliding velocity and mean deformational velocity. We find that higher values of the slip ratio generally lead to a more efficient transfer, whereas the transfer is significantly dampened for ice that attains most of its surface velocity by creep. Our findings underline the importance of bedrock topography for ice stream dynamics on spatial scales up to 20 times the mean ice thickness. Our results also suggest that local variations in the flow regime and surface topography at this spatial scale cannot be explained by variations in basal slipperiness.

scholarly journals The transferability of adjoint inversion products between different ice flow models

2021 ◽  
Vol 15 (4) ◽  
pp. 1975-2000
Author(s):  
Jowan M. Barnes ◽  
Thiago Dias dos Santos ◽  
Daniel Goldberg ◽  
G. Hilmar Gudmundsson ◽  
Mathieu Morlighem ◽  
...  
Keyword(s):  
Thickness Distribution ◽  
West Antarctica ◽  
Amundsen Sea ◽  
Ice Flow ◽  
Flow Models ◽  
Extra Effort ◽  
Direct Observations ◽  
Basal Sliding ◽  
The Subject ◽  
Over 40 Years

Abstract. Among the most important challenges faced by ice flow models is how to represent basal and rheological conditions, which are challenging to obtain from direct observations. A common practice is to use numerical inversions to calculate estimates for the unknown properties, but there are many possible methods and not one standardised approach. As such, every ice flow model has a unique initialisation procedure. Here we compare the outputs of inversions from three different ice flow models, each employing a variant of adjoint-based optimisation to calculate basal sliding coefficients and flow rate factors using the same observed surface velocities and ice thickness distribution. The region we focus on is the Amundsen Sea Embayment in West Antarctica, the subject of much investigation due to rapid changes in the area over recent decades. We find that our inversions produce similar distributions of basal sliding across all models, despite using different techniques, implying that the methods used are highly robust and represent the physical equations without much influence by individual model behaviours. Transferring the products of inversions between models results in time-dependent simulations displaying variability on the order of or lower than existing model intercomparisons. Focusing on contributions to sea level, the highest variability we find in simulations run in the same model with different inversion products is 32 %, over a 40-year period, a difference of 3.67 mm. There is potential for this to be improved with further standardisation of modelling processes, and the lowest variability within a single model is 13 %, or 1.82 mm over 40 years. While the successful transfer of inversion outputs from one model to another requires some extra effort and technical knowledge of the particular models involved, it is certainly possible and could indeed be useful for future intercomparison projects.

scholarly journals The bedrock topography of Starbuck Glacier, Antarctic Peninsula, as determined by radio-echo soundings and flow modeling

2014 ◽  
Vol 55 (67) ◽  
pp. 22-28 ◽  
Author(s):  
Daniel Farinotti ◽  
Edward C. King ◽  
Anika Albrecht ◽  
Matthias Huss ◽  
G. Hilmar Gudmundsson
Keyword(s):  
Antarctic Peninsula ◽  
Thickness Distribution ◽  
Flow Speed ◽  
Ice Thickness ◽  
Ice Flow ◽  
Bedrock Topography ◽  
Radio Echo Sounding ◽  
Field Season ◽  
Thickness Measurements

AbstractA glacier-wide ice-thickness distribution and bedrock topography is presented for Starbuck Glacier, Antarctic Peninsula. The results are based on 90 km of ground-based radio-echo sounding lines collected during the 2012/13 field season. Cross-validation with ice-thickness measurements provided by NASA's IceBridge project reveals excellent agreement. Glacier-wide estimates are derived using a model that calculates distributed ice thickness, calibrated with the radio-echo soundings. Additional constraints are obtained from in situ ice flow-speed measurements and the surface topography. The results indicate a reverse-sloped bed extending from a riegel occurring ~ 5 km upstream of the current grounding line. The deepest parts of the glacier are as much as 500 m below sea level. The calculated total volume of 80.7 ± 7.2 km3 corresponds to an average ice thickness of 312 ± 30 m.

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