scholarly journals Subglacial landforms beneath Rutford Ice Stream, Antarctica: detailed bed topography from ice-penetrating radar

2016 ◽  
Vol 8 (1) ◽  
pp. 151-158 ◽  
Author(s):  
Edward C. King ◽  
Hamish D. Pritchard ◽  
Andrew M. Smith
Keyword(s):  
Surface Elevation ◽  
Baseline Survey ◽  
Polar Regions ◽  
Active System ◽  
Data Set ◽  
Bed Topography ◽  
Ice Stream ◽  
Elevation Data ◽  
Radio Echo Sounding ◽  
Elevation Model

Abstract. We present a digital elevation model of the bed of Rutford Ice Stream, Antarctica, derived from radio-echo sounding data. The data cover an 18  ×  40 km area immediately upstream of the grounding line of the ice stream. This area is of particular interest because repeated seismic surveys have shown that rapid erosion and deposition of subglacial sediments has taken place. The bed topography shows a range of different subglacial landforms including mega-scale glacial lineations, drumlins and hummocks. This data set will form a baseline survey which, when compared to future surveys, should reveal how active subglacial landscapes change over time. These data also allow comparison between subglacial landforms in an active system with those observed in deglaciated areas in both polar regions. The data set comprises observed ice thickness data, an interpolated bed elevation grid, observed surface elevation data and a surface elevation grid. The data set is available at http://doi.org/269.

scholarly journals Subglacial landforms beneath Rutford Ice Stream, Antarctica: detailed bed topography from ice-penetrating radar

2015 ◽  
Vol 8 (2) ◽  
pp. 913-934
Author(s):  
E. C. King ◽  
H. D. Pritchard ◽  
A. M. Smith
Keyword(s):  
Surface Elevation ◽  
Baseline Survey ◽  
Polar Regions ◽  
Active System ◽  
Bed Topography ◽  
Ice Stream ◽  
Digital Elevation ◽  
Elevation Data ◽  
Radio Echo Sounding ◽  
Elevation Model

Abstract. We present a digital elevation model of the bed of Rutford Ice Stream, Antarctica derived from radio-echo sounding data. The data cover an 18 km × 40 km area immediately upstream of the grounding line of the ice stream. This area is of particular interest because repeated seismic surveys have shown that rapid erosion and deposition of subglacial sediments has taken place. The bed topography shows a range of different subglacial landforms including mega-scale glacial lineations, drumlins and hummocks. This dataset will form a baseline survey which, when compared to future surveys, should reveal how active subglacial landscapes change over time. These data also allow comparison between subglacial landforms in an active system with those observed in deglaciated areas in both polar regions. The dataset comprises observed ice thickness data, an interpolated bed elevation grid, observed surface elevation data and a surface elevation grid. The dataset is available at http://doi.org/269.

scholarly journals Ice stream or not? Radio-echo sounding of Carlson Inlet, West Antarctica

2011 ◽  
Vol 5 (4) ◽  
pp. 907-916 ◽  
Author(s):  
E. C. King
Keyword(s):  
West Antarctica ◽  
Ice Streams ◽  
Basal Resistance ◽  
Bed Topography ◽  
Ice Stream ◽  
Time Period ◽  
Adjacent Part ◽  
Radio Echo Sounding ◽  
History Of ◽  
Fast Flow

Abstract. The Antarctic Ice Sheet loses mass to the surrounding ocean mainly by drainage through a network of ice streams: fast-flowing glaciers bounded on either side by ice flowing one or two orders of magnitude more slowly. Ice streams flow despite low driving stress because of low basal resistance but are known to cease flowing if the basal conditions change, which can take place when subglacial sediment becomes dewatered by freezing or by a change in hydraulic pathways. Carlson Inlet, Antarctica has been interpreted as a stagnated ice stream, based on surface and basal morphology and shallow radar reflection profiling. To resolve the question of whether the flow history of Carlson Inlet has changed in the past, I conducted a ground-based radar survey of Carlson Inlet, the adjacent part of Rutford Ice Stream, and Talutis Inlet, West Antarctica. This survey provides details of the internal ice stratigraphy and allows the flow history to be interpreted. Tight folding of isochrones in Rutford Ice Stream and Talutis Inlet is interpreted to be the result of lateral compression during convergent flow from a wide catchment into a narrow, fast-flowing trunk. In contrast, the central part of Carlson Inlet has gently-folded isochrones that drape over the bed topography, suggestive of local accumulation and slow flow. A 1-D thermo-mechanical model was used to estimate the age of the ice. I conclude that the ice in the centre of Carlson Inlet has been near-stagnant for between 3500 and 6800 yr and that fast flow has not occurred there during that time period.

scholarly journals On elevation models as input for mass-balance calculations of the Greenland ice sheet

1996 ◽  
Vol 23 ◽  
pp. 181-186 ◽  
Author(s):  
R. S. W. van de Wal ◽  
S. Ekholm
Keyword(s):  
Marginal Zone ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Balance Model ◽  
Data Sets ◽  
Differential Gps ◽  
Data Set ◽  
Radio Echo Sounding ◽  
The Difference ◽  
Elevation Model

In this paper the elevation model for the Greenland ice sheet based upon radio-echo-sounding flights of the Technical University of Denmark (TUD) (Letréguilly and others, 1991) are compared with the satellite-altimetry model (Tscherning and others, 1993) improved with airborne-laser and radar altimetry (IA model). Although the general hypsometry of both data sets is rather similar, differences seem to be large at individual points along the ice margin. Over the entire ice sheet, the difference between the IA model and the TUD model is 33 m with a root-mean-square error of 112 m. Differential GPS measurements collected in the ice-marginal zone near Søndre Strømfjord show that the IA model is more accurate than the TUD model. The latter data set underestimates the elevation by approximately 150 m in the ice-marginal zone near Søndre Strømfjord.Calculation of the ablation with an energy-balance model and with a degree-day model points to a 20% decrease in the ablation if the IA model is used. Not only does this show the sensitivity of ablation calculations to the orographic input but it also indicates that the ablation calculated by the models used nowadays is relatively overestimated.

scholarly journals Ice flow in the northeast Greenland ice stream

2000 ◽  
Vol 31 ◽  
pp. 141-146 ◽  
Author(s):  
Ian R. Joughin ◽  
Mark A. Fahnestock ◽  
Jonathan L. Bamber
Keyword(s):  
Velocity Field ◽  
Flow Velocity ◽  
Sar Interferometry ◽  
Data Set ◽  
Ice Flow ◽  
Ice Stream ◽  
Global Positioning ◽  
Slow Moving ◽  
The Subject ◽  
Elevation Model

AbstractWe have measured ice flow and detailed topography in northeastern Greenland using satellite-based synthetic-aperture radar (SAR) interferometry. The subject of this study is the large ice stream that drains this quadrant of the ice sheet. A single SAR interferogram allows the measurement of one component of motion over a several-day-long interval. We have used a set of such measurements from multiple look directions to produce a mosaic of ice-flow velocity. The resulting flow field is tied to an estimated balance-velocity distribution in slow-moving areas and assumes flow to be locally surface-parallel. The velocity field is the most detailed, consistent data-set available over a flow feature of this size. It compares with global positioning system surveyed velocity measurements at the 5 m a–1 level In the process of mapping ice-flow velocity an enhanced elevation model of the ice stream was produced. The elevation model is based on a blend of interferometrically measured short-wavelength topography and radar-altimetry-determined longer-wavelength topography. This enhanced model has improved information on local surface slope, which is useful for estimating the horizontal components of the velocity field.

scholarly journals Use of historical elevation data to calculate surface-elevation and volume changes of Ha-Iltzuk Icefield, southwest British Columbia, Canada, 1970 to mid-1980s

2011 ◽  
Vol 52 (59) ◽  
pp. 109-115 ◽  
Author(s):  
Jeffrey A. VanLooy ◽  
Richard R. Forster
Keyword(s):  
British Columbia ◽  
Average Rate ◽  
Meteorological Data ◽  
Surface Elevation ◽  
Volume Changes ◽  
Digital Elevation ◽  
Elevation Data ◽  
Elevation Changes ◽  
Elevation Model ◽  
Thinning Rate

AbstractInvestigations into glacial changes, including understanding variations in the rates of glacial volume and surface-elevation changes, have increased over the past decade. This study uses historical glacier elevation data in the form of topographic maps from 1970 and a digital elevation model from the mid-1980s to calculate surface-elevation and volume changes for Ha-Iltzuk Icefield, southwest British Columbia, Canada. Results indicate that the icefield thinned at an average rate of 0.76±0.25 ma–1 during this period. A previous study of Ha-Iltzuk Icefield also using the geodetic method found a thinning rate of 1.0±0.20ma–1 between the mid-1980s and 1999, indicating a slight increase in the amount of icefield thinning. Within the ablation zone, thinning increased with decreasing elevation at a rate of 1.9±0.68 ma–1 km–1 between these two periods (1970 to mid-1980s versus mid-1980s to 1999). Analysis of meteorological data suggests that increases in both temperature and rainfall, as well as decreases in snowfall, likely contributed to the increased thinning rate.

scholarly journals Perancangan Program Peramalan Kanal Banjir Barat Jakarta Menggunakan Autoregresi Multivariant

2012 ◽  
Vol 3 (1) ◽  
pp. 186
Author(s):  
Ngarap Im Manik
Keyword(s):  
Water Surface ◽  
Equation Model ◽  
Water Levels ◽  
Surface Elevation ◽  
Coefficient Of Determination ◽  
Water Surface Elevation ◽  
A Value ◽  
Water Gate ◽  
Elevation Data ◽  
Elevation Model

This paper discusses the design of computer programs that is able to discern the characteristics description of water surface elevation data in Manggarai water gate, which variable is the most influential on the water surface elevation model and find a proper flood forecasting model using multivariate autoregressive model. The result of this study is able to assist the water gate officer in delivering early warning, prevention and anticipation of flood countermeasure. The forecast equation model obtained is Yt = 109,.7828 + 0,9291 CHt-6 – 24,484 T t-2 – 0,06245 PM t-2 + 1,4706 KB t-2 in which temperature and water surface elevation is a variable that owns the strongest correlation. This variable owns negative correlation which means that if the temperature falls, the water levels will rise. The coefficient of determination has a value of R2 = 0.4056 and the Durbin Watson statistics for DW = 0.7429.

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 On elevation models as input for mass-balance calculations of the Greenland ice sheet

1996 ◽  
Vol 23 ◽  
pp. 181-186 ◽  
Author(s):  
R. S. W. van de Wal ◽  
S. Ekholm
Keyword(s):  
Marginal Zone ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Balance Model ◽  
Data Sets ◽  
Differential Gps ◽  
Data Set ◽  
Radio Echo Sounding ◽  
The Difference ◽  
Elevation Model

In this paper the elevation model for the Greenland ice sheet based upon radio-echo-sounding flights of the Technical University of Denmark (TUD) (Letréguilly and others, 1991) are compared with the satellite-altimetry model (Tscherning and others, 1993) improved with airborne-laser and radar altimetry (IA model). Although the general hypsometry of both data sets is rather similar, differences seem to be large at individual points along the ice margin. Over the entire ice sheet, the difference between the IA model and the TUD model is 33 m with a root-mean-square error of 112 m. Differential GPS measurements collected in the ice-marginal zone near Søndre Strømfjord show that the IA model is more accurate than the TUD model. The latter data set underestimates the elevation by approximately 150 m in the ice-marginal zone near Søndre Strømfjord. Calculation of the ablation with an energy-balance model and with a degree-day model points to a 20% decrease in the ablation if the IA model is used. Not only does this show the sensitivity of ablation calculations to the orographic input but it also indicates that the ablation calculated by the models used nowadays is relatively overestimated.

scholarly journals Co-registration of an Antarctic digital elevation model with SSM/I brightness temperatures

1993 ◽  
Vol 17 ◽  
pp. 93-97 ◽  
Author(s):  
J.D. Wilson ◽  
K.C. Jezek
Keyword(s):  
Brightness Temperature ◽  
Digital Elevation Model ◽  
Ice Sheet ◽  
Polar Regions ◽  
Cd Rom ◽  
Brightness Temperatures ◽  
Digital Elevation ◽  
Elevation Data ◽  
Polar Ice Sheets ◽  
Elevation Model

The Special Sensor Microwave/Imager (SMM/I) instrument provides daily measures of microwave brightness temperatures Tb over the polar regions. Data are available from 1987 to the present and have a demonstrated utility for sea-ice studies. In this paper we investigate applications to polar ice sheets with a view towards correlating patterns of Tb with ice-sheet elevation. We go on to discuss the Tb signature of processes linked to temperature anomalies and accumulation zone boundaries. Our approach consists of combining SSM/I Tb values provided on CD-ROM by the National Snow and Ice Data Center (NSIDC) with a digital elevation model (DEM) of Antarctica derived originally from the Scott Polar Research Institute Antarctic Map Folio. We focused on 37 GHz data which is mapped onto a 316 × 332 polar stereographic grid at 25 km resolution. The DEM consists of a 281 × 281 array of elevation values with a 20 km resolution. The DEM was resampled to be compatible with the SSM/I data by transforming the elevation data from the original projection place to geodetic coordinates. The elevation data were than transformed onto the SSM/I projection plane. Elevation data were interpolated to yield ice-sheet surface heights at 25 km intervals coinciding with SSM/I point Tb assignments. By co-registering the two data sets, it is possible to “drape” the brightness temperature data over the elevation data. The resulting image highlights the relationship (and variations) between ice-sheet topography and brightness temperature.

scholarly journals Bed properties and hydrological conditions underneath McCall Glacier, Alaska, USA

2009 ◽  
Vol 50 (51) ◽  
pp. 80-84 ◽  
Author(s):  
Frank Pattyn ◽  
Charlotte Delcourt ◽  
Denis Samyn ◽  
Bert de Smedt ◽  
Matt Nolan
Keyword(s):  
Potential Gradient ◽  
Ice Thickness ◽  
Central Frequency ◽  
Bed Topography ◽  
Ice Volume ◽  
Arctic Alaska ◽  
Digital Elevation ◽  
Basal Sliding ◽  
Radio Echo Sounding ◽  
Elevation Model

AbstractDuring three summer field seasons (2003, 2005 and 2006) we carried out radio-echo sounding measurements with a 5MHz (central frequency) ice-penetrating radar on McCall Glacier, Arctic Alaska, USA, along the central flowline and 17 cross-profiles. Two-way travel time was, after migration, converted to ice thickness, which, in combination with a recent digital elevation model of the surface of the glaciated area, resulted in a detailed map of the bed topography. This reveals a complex basal topography in the confluence area of the different glacial cirques. The pattern of subglacial water flow following the hydraulic potential gradient was calculated for the whole glacier area and shows a confluence of subglacial water downstream from the confluence of the glacier cirques. From the ice-thickness map the total ice volume was estimated as slightly less than 0.5 km3. Bed reflection power (BRP) was determined for the glacier after correction for ice-thickness dependence. Results reveal a clear relationship between the BRP pattern and basal sliding anomalies along the central flowline.

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