MONITORING SUB-WEEKLY EVOLUTION OF SURFACE VELOCITY AND ELEVATION FOR A HIGH-LATITUDE SURGING GLACIER USING SENTINEL-2

Abstract. Currently, the Sentinel-2 twin satellite constellation of the Copernicus program is in operational mode and generates high repeat acquisitions at high-latitudes during polar day. These pushbroom satellites have a large field-of-view and are therefore ideal for simultaneous extraction of glacier displacement and elevation data. In this study we showcase the capabilities of this system set-up by generating time-series of glacier flow and elevation change over Negribreen, a tidewater glacier in Svalbard which nowadays is in its surge phase.

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Proglacial Lakes Elevate Glacier Surface Velocities in the Himalayan Region

10.5194/egusphere-egu21-13311 ◽

2021 ◽

Author(s):

Jan Bouke Pronk ◽

Tobias Bolch ◽

Owen King ◽

Bert Wouters ◽

Douglas Benn

Keyword(s):

Flow Line ◽

Surface Velocity ◽

Glacier Surface ◽

Ice Flow ◽

Mass Losses ◽

Himalayan Glaciers ◽

Large Heterogeneity ◽

Glacier Flow ◽

The Ganges ◽

Sentinel 2

Meltwater from Himalayan glaciers sustains the flow of rivers such as the Ganges and Brahmaputra on which over half a billion people depend for day-to-day needs. Upstream areas are likely to be affected substantially by climate change, and changes in the magnitude and timing of meltwater supply are likely to occur in coming decades. About 10 % of the Himalayan glacier population terminates into pro-glacial lakes and such lake-terminating glaciers are known to be capable of accelerating total mass losses. However, relatively little is known about the mechanisms driving exacerbated ice loss from lake-terminating glaciers in the Himalaya. Here we examine a 2017-2019 glacier surface velocity dataset, derived from Sentinel 2 imagery, covering most of the Central and Eastern Himalayan glaciers larger than 3 km2. We find that centre flow line velocities of lake-terminating glaciers are more than double those of land-terminating glaciers (18.8 vs 8.24 m yr-1) and show substantially more heterogeneity around glacier termini. We attribute this large heterogeneity to the varying influence of lakes on glacier dynamics, resulting in differential rates of dynamic thinning, which effects about half of the clean-ice lake-terminating glacier population. Also, numerical ice-flow model experiments suggest that changes at the frontal boundary condition can play a key role in accelerating the glacier flow at the front. With continued warming new lake development is likely to happen and will further accelerate future ice mass losses, a scenario not currently considered in regional projections.&#160;

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Proglacial Lakes Elevate Glacier Surface Velocities in the Himalayan Region

10.5194/tc-2021-90 ◽

2021 ◽

Author(s):

Jan Bouke Pronk ◽

Tobias Bolch ◽

Owen King ◽

Bert Wouters ◽

Douglas I. Benn

Keyword(s):

Flow Line ◽

Surface Velocity ◽

Glacial Lakes ◽

Glacier Surface ◽

Ice Flow ◽

Himalayan Glaciers ◽

Large Heterogeneity ◽

Glacier Flow ◽

The Ganges ◽

Sentinel 2

Abstract. Meltwater from Himalayan glaciers sustains the flow of rivers such as the Ganges and Brahmaputra on which over half a billion people depend for day-to-day needs. Upstream areas are likely to be affected substantially by climate change, and changes in the magnitude and timing of meltwater supply are likely to occur in coming decades. About 10 % of the Himalayan glacier population terminates into pro-glacial lakes and such lake-terminating glaciers are known to exhibit higher than average total mass losses. However, relatively little is known about the mechanisms driving exacerbated ice loss from lake-terminating glaciers in the Himalaya. Here we examine a composite (2017–2019) glacier surface velocity dataset, derived from Sentinel 2 imagery, covering Central and Eastern Himalayan glaciers larger than 3 km2. We find that centre flow line velocities of lake-terminating glaciers are more than double those of land-terminating glaciers (18.8 vs 8.24 m yr−1) and show substantially more heterogeneity around glacier termini. We attribute this large heterogeneity to the varying influence of lakes on glacier dynamics, resulting in differential rates of dynamic thinning, which effects about half of the clean-ice lake-terminating glacier population. Numerical ice-flow model experiments show that changes at the frontal boundary condition are likely to play a key role in accelerating the glacier flow at the front, with variations in basal friction only being of modest importance. The expansion of current glacial lakes, and the formation of new meltwater bodies will influence the dynamics of an increasing number of Himalayan glaciers in the future; a scenario not currently considered in regional ice loss projections.

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Evaluating the repeatability and set-up sensitivity of a large field of view distortion phantom and software for magnetic resonance-only radiotherapy

Physics and Imaging in Radiation Oncology ◽

10.1016/j.phro.2018.04.005 ◽

2018 ◽

Vol 6 ◽

pp. 31-38 ◽

Cited By ~ 9

Author(s):

Jonathan Wyatt ◽

Stephen Hedley ◽

Emily Johnstone ◽

Richard Speight ◽

Charles Kelly ◽

...

Keyword(s):

Magnetic Resonance ◽

Field Of View ◽

Large Field ◽

Set Up

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Towards clinical grating-interferometry mammography

European Radiology ◽

10.1007/s00330-019-06362-x ◽

2019 ◽

Vol 30 (3) ◽

pp. 1419-1425 ◽

Cited By ~ 9

Author(s):

Carolina Arboleda ◽

Zhentian Wang ◽

Konstantins Jefimovs ◽

Thomas Koehler ◽

Udo Van Stevendaal ◽

...

Keyword(s):

Breast Cancer ◽

Cancer Detection ◽

Dark Field ◽

Breast Cancer Detection ◽

Field Of View ◽

Large Field ◽

Clinical Environment ◽

Conventional Mammography ◽

Grating Interferometer ◽

Set Up

Abstract Objectives Grating-interferometry-based mammography (GIM) might facilitate breast cancer detection, as several research works have demonstrated in a pre-clinical setting, since it is able to provide attenuation, differential phase contrast, and scattering images simultaneously. In order to translate this technique to the clinics, it has to be adapted to cover a large field-of-view within a clinically acceptable exposure time and radiation dose. Methods We set up a grating interferometer that fits into a standard mammography system and fulfilled the aforementioned conditions. Here, we present the first mastectomy images acquired with this experimental device. Results and conclusion Our system performs at a mean glandular dose of 1.6 mGy for a 5-cm-thick, 18%-dense breast, and a field-of-view of 26 × 21 cm2. It seems to be well-suited as basis for a clinical-environment device. Further, dark-field signals seem to support an improved lesion visualization. Evidently, the effective impact of such indications must be evaluated and quantified within the context of a proper reader study. Key Points • Grating-interferometry-based mammography (GIM) might facilitate breast cancer detection, since it is sensitive to refraction and scattering and thus provides additional tissue information. • The most straightforward way to do grating-interferometry in the clinics is to modify a standard mammography device. • In a first approximation, the doses given with this technique seem to be similar to those of conventional mammography.

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Contrasting surface velocities between lake- and land-terminating glaciers in the Himalayan region

The Cryosphere ◽

10.5194/tc-15-5577-2021 ◽

2021 ◽

Vol 15 (12) ◽

pp. 5577-5599

Author(s):

Jan Bouke Pronk ◽

Tobias Bolch ◽

Owen King ◽

Bert Wouters ◽

Douglas I. Benn

Keyword(s):

Flow Line ◽

Force Balance ◽

Surface Velocity ◽

Glacier Surface ◽

Ice Flow ◽

Himalayan Glaciers ◽

Large Heterogeneity ◽

Glacier Flow ◽

The Ganges ◽

Sentinel 2

Abstract. Meltwater from Himalayan glaciers sustains the flow of rivers such as the Ganges and Brahmaputra on which over half a billion people depend for day-to-day needs. Upstream areas are likely to be affected substantially by climate change, and changes in the magnitude and timing of meltwater supply are expected to occur in coming decades. About 10 % of the Himalayan glacier population terminates into proglacial lakes, and such lake-terminating glaciers are known to exhibit higher-than-average total mass losses. However, relatively little is known about the mechanisms driving exacerbated ice loss from lake-terminating glaciers in the Himalaya. Here we examine a composite (2017–2019) glacier surface velocity dataset, derived from Sentinel 2 imagery, covering central and eastern Himalayan glaciers larger than 3 km2. We find that centre flow line velocities of lake-terminating glaciers (N = 70; umedian: 18.83 m yr−1; IQR – interquartile range – uncertainty estimate: 18.55–19.06 m yr−1) are on average more than double those of land-terminating glaciers (N = 249; umedian: 8.24 m yr−1; IQR uncertainty estimate: 8.17–8.35 m yr−1) and show substantially more heterogeneity than land-terminating glaciers around glacier termini. We attribute this large heterogeneity to the varying influence of lakes on glacier dynamics, resulting in differential rates of dynamic thinning, which causes about half of the lake-terminating glacier population to accelerate towards the glacier termini. Numerical ice-flow model experiments show that changes in the force balance at the glacier termini are likely to play a key role in accelerating the glacier flow at the front, with variations in basal friction only being of modest importance. The expansion of current glacial lakes and the formation of new meltwater bodies will influence the dynamics of an increasing number of Himalayan glaciers in the future, and these factors should be carefully considered in regional projections.

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