What is a Glacier? Assessing Ice Dynamic Thresholds

2021 ◽  
Author(s):  
Caitlyn Florentine
Keyword(s):  
Science Communication ◽  
Stress Sensitivity ◽  
Ice Thickness ◽  
Median Surface ◽  
Policy Makers ◽  
Material Density ◽  
Elevation Data ◽  
Order Of Magnitude ◽  
Mapping Techniques ◽  
Thickness Measurements

<p>The current global Randolph Glacier Inventory (RGI V6) minimum area cutoff is 0.01 km<sup>2</sup>. Including features this small empowers comprehensive assessments of global glacier water resources. It also enables high-resolution glacier hindcasts, ensuring that sites where modern glacier extent is now diminutive are charted and not overlooked. Yet the automated and manual mapping techniques used to generate RGI glacier outlines do not necessarily discriminate based on ice motion. There is currently no RGI mask that discerns between glaciers that likely still deform under their own weight (classic glacier) versus glaciers that are unlikely to satisfy this criterion (stagnant ice patch). Here is a highly simplified, data-driven attempt to develop a globally complete ice dynamic mask. Features are treated as simple slabs, with area given by the RGI database, order of magnitude thickness derived from volume-area power law scaling, and median surface slope derived from topography data (RGI-TOPO dataset, beta release). Driving stress is calculated using these inputs and assuming material density 900 kg m<sup>-3</sup>. This is repeated using varying elevation data sources, the globally complete consensus ice thickness estimate, and sparse direct ice thickness measurements (GlaThiDa), to explore driving stress sensitivity to different slab representations. Slabs with driving stress less than 10<sup>5</sup> Pa are interpreted as features where the ambient driving stress is insufficient to overcome the yield strength of ice. Uncertainty analysis and comparison against ice motion observations determines if these sub 10<sup>5</sup> Pa slab features reliably mask RGI glaciers that are no longer in motion. This approach serves as a first cut at developing a reproducible, systematic way of discerning between classic glaciers (bodies of ice that move) versus other cryosphere features. This may enhance consistency across technical analyses within the glaciological research community and science communication with policy makers.</p>

scholarly journals Coherent radar ice thickness measurements over the Greenland ice sheet

2001 ◽  
Vol 106 (D24) ◽  
pp. 33761-33772 ◽  
Author(s):  
S. Gogineni ◽  
D. Tammana ◽  
D. Braaten ◽  
C. Leuschen ◽  
T. Akins ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Thickness ◽  
Coherent Radar ◽  
Thickness Measurements

scholarly journals Measuring and inferring the ice thickness distribution of four glaciers in the Tien Shan, Kyrgyzstan

2020 ◽  
pp. 1-18
Author(s):  
Lander Van Tricht ◽  
Philippe Huybrechts ◽  
Jonas Van Breedam ◽  
Johannes J. Fürst ◽  
Oleg Rybak ◽  
...  
Keyword(s):  
Cross Validation ◽  
Thickness Distribution ◽  
Tien Shan ◽  
Ice Thickness ◽  
Ice Volume ◽  
In Situ Data ◽  
Radio Echo Sounding ◽  
Thickness Measurements ◽  
Tien Shan Mountains

Abstract Glaciers in the Tien Shan mountains contribute considerably to the fresh water used for irrigation, households and energy supply in the dry lowland areas of Kyrgyzstan and its neighbouring countries. To date, reconstructions of the current ice volume and ice thickness distribution remain scarce, and accurate data are largely lacking at the local scale. Here, we present a detailed ice thickness distribution of Ashu-Tor, Bordu, Golubin and Kara-Batkak glaciers derived from radio-echo sounding measurements and modelling. All the ice thickness measurements are used to calibrate three individual models to estimate the ice thickness in inaccessible areas. A cross-validation between modelled and measured ice thickness for a subset of the data is performed to attribute a weight to every model and to assemble a final composite ice thickness distribution for every glacier. Results reveal the thickest ice on Ashu-Tor glacier with values up to 201 ± 12 m. The ice thickness measurements and distributions are also compared with estimates composed without the use of in situ data. These estimates approach the total ice volume well, but local ice thicknesses vary substantially.

scholarly journals High-resolution ice-thickness mapping in South Greenland

2014 ◽  
Vol 55 (67) ◽  
pp. 64-70 ◽  
Author(s):  
M. Morlighem ◽  
E. Rignot ◽  
J. Mouginot ◽  
H. Seroussi ◽  
E. Larour
Keyword(s):  
High Resolution ◽  
Optimization Problems ◽  
Mass Conservation ◽  
Ice Thickness ◽  
Soft Constraint ◽  
Hard Constraint ◽  
Conservation Of Mass ◽  
Motion Data ◽  
Geostatistical Techniques ◽  
Thickness Measurements

AbstractAirborne radar sounding is difficult in South Greenland because of the presence of englacial water, which prevents the signal from reaching the bed. Data coverage remains suboptimal for traditional methods of ice-thickness and bed mapping that rely on geostatistical techniques, such as kriging, because important features are missing. Here we apply two alternative approaches of high-resolution (~300m) ice-thickness mapping, that are based on the conservation of mass, to two regions of South Greenland: (1) Qooqqup Sermia and Kiattuut Sermiat, and (2) Ikertivaq. These two algorithms solve optimization problems, for which the conservation of mass is either enforced as a hard constraint, or as a soft constraint. For the first region, very few measurements are available but there is no gap in ice motion data, whereas for Ikertivaq, more ice-thickness measurements are available, but there are gaps in ice motion data. We show that mass-conservation algorithms can be used as validation tools for radar sounding. We also show that it is preferable to apply mass conservation as a hard constraint, rather than a soft constraint, as it better preserves elongated features, such as glacial valleys and ridges.

A Portable Radar for Ice Thickness Measurements

1994 ◽  
Author(s):  
Martti Toikka ◽  
Pertti Vainikainen
Keyword(s):  
Ice Thickness ◽  
Thickness Measurements

Automatic Plotting of Airborne Geophysical Survey Data

1972 ◽  
Vol 25 (2) ◽  
pp. 162-175 ◽  
Author(s):  
B. M. Ewen Smith
Keyword(s):  
Dead Reckoning ◽  
Geophysical Survey ◽  
The Other ◽  
Ice Thickness ◽  
Terminal Position ◽  
The World ◽  
Geophysical Measurement ◽  
The Antarctic ◽  
Thickness Measurements ◽  
Geophysical Measurements

When geophysical measurements are made from the air, it is important to know the position of the aircraft. The position at any time is usually known from a combination of position-fixing and dead-reckoning systems. In-flight optimization of this combination is a well-studied subject. When post-flight track plotting is required for geophysical survey, use can be made of both the initial and terminal position fixes to correct the dead-reckoning track and hence improve on the in-flight version. This technique is applied to compute the track of aircraft conducting ice thickness measurements in the Antarctic, and the effect of certain errors is evaluated. The algebraic results are equally applicable in parts of the world where better navigational aids are available. A relation is derived between the track plotting errors and die errors in the geophysical measurement such that the precision of one is not degraded by errors in the other.

scholarly journals Ice thickness measurements at freshwater lake and river using GLONASS and GPS signals

2017 ◽  
Vol 14 (2) ◽  
pp. 167-174
Author(s):  
M.I. Mikhailov ◽  
◽  
K.V. Muzalevskiy ◽  
V.L. Mironov ◽  
◽  
...  
Keyword(s):  
Freshwater Lake ◽  
Ice Thickness ◽  
Thickness Measurements

scholarly journals Science communication between researchers and policy makers. Reflections from a European project

2012 ◽  
Vol 11 (03) ◽  
pp. C07 ◽  
Author(s):  
Paola Rodari ◽  
Karen Bultitude ◽  
Karen Desborough
Keyword(s):  
Crucial Role ◽  
Science Communication ◽  
Policy Makers ◽  
European Project ◽  
Research Outcomes ◽  
Research Findings ◽  
The Impact

The SCOOP project aimed to maximise the potential for the transfer of research findings into policy using European-funded socio-economic sciences and humanities research. The project incorporated a News Alert Service to communicate policy-relevant elements of research findings to interested stakeholders. It also sought to further develop the skills of researchers to effectively communicate research outcomes to policy makers through a programme of Masterclasses. A series of evaluation surveys were held to both tailor the project outputs to the target audiences, and to measure the impact of project actions on the interactions between SSH researchers and policy makers. Both SCOOP elements were well received, with evidence of improved communication, utilisation of SSH research by policy makers, and greater awareness and proactivity on the part of the researchers. More generally, interviews and questionnaire findings demonstrated that mediators play a crucial role: various intermediaries and interpreters work between policy makers and researchers to put in context the research outcomes and convey information through dedicated channels and formalised processes as well as informal, fluid processes.

scholarly journals Geometry and Dynamics of a Surge-type Glacier

1977 ◽  
Vol 18 (79) ◽  
pp. 181-194 ◽  
Author(s):  
R. Bindschadler ◽  
W. D. Harrison ◽  
C. F. Raymond ◽  
R. Crosson
Keyword(s):  
Steady State ◽  
Stress Distribution ◽  
Internal Stress ◽  
Ice Thickness ◽  
Surface Slope ◽  
Local Surface ◽  
Order Of Magnitude ◽  
Internal Deformation ◽  
Longitudinal Profiles ◽  
Similar Depth

AbstractMeasurement of geometry, motion, and mass balance from Variegated Glacier, Alaska portray conditions in this surge-type glacier close to the mid-point of its 20 year surge cycle. Comparison of longitudinal profiles of ice depth, surface slope, and surface speed indicate that the motion occurs largely by internal deformation assuming the ice deforms according to the experimental law of Glen. Surface speed is not noticeably affected by local surface slope on the scale of the ice thickness or smaller, but correlates well with slope determined on a longitudinal averaging scale about one order of magnitude larger than the ice depth. The rate of motion on Variegated Glacier agrees well with rates on non-surge type temperate glaciers which have similar depth and slope. Although the (low regime at the time of the measurements is apparently typical of temperate glaciers, a large discrepancy between the balance flux needed for steady state and the actual flux is indicative of a rapidly changing surface elevation profile and internal stress distribution.

scholarly journals Flow of Rutford Ice Stream and Comparison with Carlson Inlet, Antarctica

1989 ◽  
Vol 12 ◽  
pp. 51-56 ◽  
Author(s):  
R.M. Frolich ◽  
D.G. Vaughan ◽  
C.S.M. Doake
Keyword(s):  
Surface Expression ◽  
Ice Thickness ◽  
Shear Stresses ◽  
Lateral Shear ◽  
Ice Stream ◽  
Grounding Line ◽  
Subglacial Topography ◽  
Characteristic Features ◽  
Basal Shear ◽  
Thickness Measurements

Results from movement surveys on Rutford Ice Stream are presented with complementary surface-elevation and ice-thickness measurements. Surface velocities of 300 m a−1 occur at least 130 km up-stream of the grounding line and contrast strongly with the neighbouring Carlson Inlet, where a velocity of 7 m a−1 has been measured. This contrast in velocity is not topographically controlled but appears to be due instead to differences in basal conditions, with Carlson Inlet probably being frozen to its bed. Concentration of lateral shear close to the margins and surface expression of subglacial topography both support a view of significant basal shear stresses in the central part of Rutford Ice Stream. The pattern of principal strain-rate trajectories shows a small number of characteristic features which can be compared with results from future modelling of the glacier's flow.

scholarly journals Comparison of Electromagnetic and Seismic-Gravity Ice Thickness Measurements in East Antarctica

1975 ◽  
Vol 15 (73) ◽  
pp. 137-150 ◽  
Author(s):  
David J. Drewry
Keyword(s):  
Seismic Reflection ◽  
East Antarctica ◽  
Ice Thickness ◽  
South Pole ◽  
Victoria Land ◽  
Radio Echo Sounding ◽  
Mean Differences ◽  
Thickness Measurements ◽  
Better Than ◽  
Echo Sounding

AbstractThe errors involved in ice thickness determinations in Antarctica by seismic reflection shooting, gravity observations and radio-echo sounding are briefly discussed. Relative accuracies of 3%, 7-10% and 1.5% have been suggested. Double checks of ice depths from radar sounding in east Antarctica indicate an internal consistency of measurement for this technique of <1%. Comparison of carefully executed seismic shooting and routine radio-echo sounding results against absolute ice thickness values from two deep core drilling sites show no significant differences between these two remote methods (i.e. both are better than 1.5%).Over 60 comparisons are examined between radar ice thicknesses and over-snow measurements obtained on eight independent traverses in east Antarctica. Three traverses exhibit consistently unacceptable results-U.S. Victoria Land Traverse II (southern leg), Commonwealth Transanlarctic Expedition and the U.S.S.R. Vostok to South Pole Traverse—which probably result from misinterpretation of “noisy” seismograms. The remaining comparisons indicate mean differences, including some navigational uncertainty, of ≈3%, <8% and 5% between radio-echo and (1) seismic, (2) gravity, and (3) gravity tied to seismic determinations, respectively.

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