scholarly journals Automated detection and temporal monitoring of crevasses using remote sensing and their implications for glacier dynamics

2016 ◽  
Vol 57 (71) ◽  
pp. 81-91 ◽  
Author(s):  
Anshuman Bhardwaj ◽  
Lydia Sam ◽  
Shaktiman Singh ◽  
Rajesh Kumar
Keyword(s):  
Flow Characteristics ◽  
Surface Velocity ◽  
Average Error ◽  
Landsat 8 ◽  
Differential Gps ◽  
Swir Band ◽  
Glacier Dynamics ◽  
Glacier Flow ◽  
Shortwave Infrared ◽  
Gps Observations

AbstractDetailed studies on temporal changes of crevasses and their linkage with glacier dynamics are scarce in the Himalayan context. Observations of temporally changing surficial crevasse patterns and their orientations are suggestive of the processes that determine seasonal glacier flow characteristics. In the present study, on a Himalayan valley glacier, changing crevasse patterns and orientations were detected and mapped on Landsat 8 images in an automated procedure using the ratio of Thermal Infrared Sensor (TIRS) band 10 to Optical Land Imager (OLI) shortwave infrared (SWIR) band 6. The ratio was capable of mapping even crevasses falling under mountain shadows. Differential GPS observations suggested an average error of 3.65% and root-mean-square error of 6.32m in crevasse lengths. A year-round observation of these crevasses, coupled with field-based surface velocity measurements, provided some interesting interpretations of seasonal glacier dynamics.

Gradual build up and episodic character of glacier velocity preceding and during the surge of a Karakorum glacier enabled by open-access image-processing

2020 ◽  
Author(s):  
Ian Delaney ◽  
Saif Aati ◽  
Flavian Beaud ◽  
Shan Gremion ◽  
Surendra Adhikari ◽  
...  
Keyword(s):  
Open Access ◽  
Landsat 8 ◽  
Optical Remote Sensing ◽  
Lake Formation ◽  
Glacier Dynamics ◽  
Current Availability ◽  
Spatio Temporal ◽  
Glacier Velocity ◽  
Glacier Flow

<p>Glacier surging provides a unique opportunity to examine rapid changes in glacier sliding that occur when some glaciers alternate between slower-than-normal (quiescence) and faster-than-normal (surge) velocities. On surging glaciers, mechanical instabilities within the glacier set off a regime of fast glacier flow, which causes these glaciers to accelerate and advance. The precise processes that cause a surging remain uncertain and likely vary between glaciers. However, the uptake of studies on glacier surging over the past decade continues to yield invaluable insights in glacier dynamics. In this study, we combine optical remote sensing and numerical modeling to examine the recent surge of Shishper glacier, in the Pakistani Karakorum. This glacier started surging in 2018, showed a dramatic terminus advance that reached rates of several meters per day. In the process, it dammed the adjacent valley, forming a lake which drained in June 2019 flooding the downstream valley, damaging the Karakorum Highway and threatening nearby communities. We leverage a high spatio-temporal resolution dataset of glacier velocities, using roughly 100 open-access images, across the Landsat-8 and Sentinel-2 record, thus encompassing the quiescence (2013-2018) and surge (2018-2019) phases. We created the dataset in an updated and nearly automated workflow by using the COSI-Corr software package to calculate displacements between images combined with a unique algorithm to filter data and remove artifacts. The result consists in high-resolution velocity maps with resolution with time intervals as short as five days. Such dataset provide a complete time-series of the spatio-temporal evolution of ice-surface velocities during a surge. One of the most notable finding is that the surge onset occurs progressively. In the two years leading up to the surge, spring speed-ups became increasingly larger in than the long-term median. We further identify three periods with  surge velocities far higher than the long-term median that likely coincide with hydrological events. Two periods occur in the spring (2018 and 2019) and the third corresponds with the lake formation in the winter of 2018-2019. Finally, we establish that the surge termination coincided with the lake drainage at the end of June 2019. The current availability of open-access imagery and  glacier topography allow us to  make an increased quantity of observations and thus better quantify glacier dynamics.</p>

scholarly journals Snow Cover Monitoring with Chinese Gaofen-4 PMS Imagery and the Restored Snow Index (RSI) Method: Case Studies

2018 ◽  
Vol 10 (12) ◽  
pp. 1871 ◽  
Author(s):  
Tianyuan Zhang ◽  
Huazhong Ren ◽  
Qiming Qin ◽  
Yuanheng Sun
Keyword(s):  
Snow Cover ◽  
Global Climate ◽  
Limiting Factor ◽  
Landsat 8 ◽  
Climate Variable ◽  
Swir Band ◽  
Novel Method ◽  
Optical Imagery ◽  
Shortwave Infrared ◽  
Signal Saturation

Snow cover is an essential climate variable of the Global Climate Observing System. Gaofen-4 (GF-4) is the first Chinese geostationary satellite to obtain optical imagery with high spatial and temporal resolution, which presents unique advantages in snow cover monitoring. However, the panchromatic and multispectral sensor (PMS) onboard GF-4 lacks the shortwave infrared (SWIR) band, which is crucial for snow cover detection. To reach the potential of GF-4 PMS in snow cover monitoring, this study developed a novel method termed the restored snow index (RSI). The SWIR reflectance of snow cover is restored firstly, and then the RSI is calculated with the restored reflectance. The distribution of snow cover can be mapped with a threshold, which should be adjusted according to actual situations. The RSI was validated using two pairs of GF-4 PMS and Landsat-8 Operational Land Imager images. The validation results show that the RSI can effectively map the distribution of snow cover in these cases, and all of the classification accuracies are above 95%. Signal saturation slightly affects PMS images, but cloud contamination is an important limiting factor. Therefore, we propose that the RSI is an efficient method for monitoring snow cover from GF-4 PMS imagery without requiring the SWIR reflectance.

scholarly journals Response of glacier flow and structure to proglacial lake development and climate at Fjallsjökull, south-east Iceland

2019 ◽  
Vol 65 (250) ◽  
pp. 321-336 ◽  
Author(s):  
REBECCA DELL ◽  
RACHEL CARR ◽  
EMRYS PHILLIPS ◽  
ANDREW J. RUSSELL
Keyword(s):  
Satellite Imagery ◽  
Surface Velocity ◽  
Outlet Glacier ◽  
Lake Development ◽  
Glacier Terminus ◽  
Air Temperatures ◽  
Glacier Dynamics ◽  
Proglacial Lake ◽  
Glacier Flow ◽  
Structural Architecture

ABSTRACTOver recent decades, the number of outlet glaciers terminating in lakes in Iceland has increased in line with climate warming. The mass-balance changes of these lake-terminating outlet glaciers are sensitive to rising air temperatures, due to altered glacier dynamics and increased surface melt. This study aims to better understand the relationship between proglacial lake development, climate, glacier dynamics and glacier structure at Fjallsjökull, a large, lake-terminating outlet glacier in south-east Iceland. We used satellite imagery to map glacier terminus position and lake extent between 1973 and 2016, and a combination of aerial and satellite imagery to map the structural architecture of the glacier's terminus in 1982, 1994 and 2011. The temporal evolution of ice surface velocities between 1990 and 2018 was calculated using feature tracking. Statistically significant increases in the rate of terminus retreat and lake expansion were identified in 2001, 2009 and 2011. Our surface velocity and structural datasets revealed the development of localised flow ‘corridors’ over time, which conveyed relatively faster flow towards the glacier's terminus. We attribute the overall changes in dynamics and structural architecture at Fjallsjökull to rising air temperatures, but argue that the spatial complexities are driven by glacier specific factors, such as basal topography.

scholarly journals Interannual and Seasonal Variability of Glacier Surface Velocity in the Parlung Zangbo Basin, Tibetan Plateau

2020 ◽  
Vol 13 (1) ◽  
pp. 80
Author(s):  
Jing Zhang ◽  
Li Jia ◽  
Massimo Menenti ◽  
Shaoting Ren
Keyword(s):  
Seasonal Variability ◽  
Global Climate ◽  
Meteorological Data ◽  
Transverse Velocity ◽  
Surface Velocity ◽  
Landsat 8 ◽  
Velocity Change ◽  
Glacier Surface ◽  
Glacier Velocity ◽  
Glacier Flow

Monitoring glacier flow is vital to understand the response of mountain glaciers to environmental forcing in the context of global climate change. Seasonal and interannual variability of surface velocity in the temperate glaciers of the Parlung Zangbo Basin (PZB) has attracted significant attention. Detailed patterns in glacier surface velocity and its seasonal variability in the PZB are still uncertain, however. We utilized Landsat-8 (L8) OLI data to investigate in detail the variability of glacier velocity in the PZB by applying the normalized image cross-correlation method. On the basis of satellite images acquired from 2013 to 2020, we present a map of time-averaged glacier surface velocity and examined four typical glaciers (Yanong, Parlung No.4, Xueyougu, and Azha) in the PZB. Next, we explored the driving factors of surface velocity and of its variability. The results show that the glacier centerline velocity increased slightly in 2017–2020. The analysis of meteorological data at two weather stations on the outskirts of the glacier area provided some indications of increased precipitation during winter-spring. Such increase likely had an impact on ice mass accumulation in the up-stream portion of the glacier. The accumulated ice mass could have caused seasonal velocity changes in response to mass imbalance during 2017–2020. Besides, there was a clear winter-spring speedup of 40% in the upper glacier region, while a summer speedup occurred at the glacier tongue. The seasonal and interannual velocity variability was captured by the transverse velocity profiles in the four selected glaciers. The observed spatial pattern and seasonal variability in glacier surface velocity suggests that the winter-spring snow might be a driver of glacier flow in the central and upper portions of glaciers. Furthermore, the variations in glacier surface velocity are likely related to topographic setting and basal slip caused by the percolation of rainfall. The findings on glacier velocity suggest that the transfer of winter-spring accumulated ice triggered by mass conservation seems to be the main driver of changes in glacier velocity. The reasons that influence the seasonal surface velocity change need further investigation.

scholarly journals EXTRACTING BUILT-UP FEATURES IN COMPLEX BIOPHYSICAL ENVIRONMENTS BY USING A LANDSAT BANDS RATIO

2020 ◽  
Vol XLIV-M-2-2020 ◽  
pp. 79-85
Author(s):  
A. H. Ngandam Mfondoum ◽  
P. G. Gbetkom ◽  
R. Cooper ◽  
S. Hakdaoui ◽  
M. B. Mansour Badamassi
Keyword(s):  
Remote Sensing ◽  
Spatial Resolution ◽  
Satellite Data ◽  
Kappa Coefficient ◽  
Landsat 8 ◽  
Experimental Site ◽  
Soil Features ◽  
Mixed Pixels ◽  
Shortwave Infrared ◽  
Normalization Process

Abstract. This paper addresses the remote sensing challenging field of urban mixed pixels on a medium spatial resolution satellite data. The tentatively named Normalized Difference Built-up and Surroundings Unmixing Index (NDBSUI) is proposed by using Landsat-8 Operational Land Imager (OLI) bands. It uses the Shortwave Infrared 2 (SWIR2) as the main wavelength, the SWIR1 with the red wavelengths, for the built-up extraction. A ratio is computed based on the normalization process and the application is made on six cities with different urban and environmental characteristics. The built-up of the experimental site of Yaoundé is extracted with an overall accuracy of 95.51% and a kappa coefficient of 0.90. The NDBSUI is validated over five other sites, chosen according to Cameroon’s bioclimatic zoning. The results are satisfactory for the cities of Yokadouma and Kumba in the bimodal and monomodal rainfall zones, where overall accuracies are up to 98.9% and 97.5%, with kappa coefficients of 0.88 and 0.94 respectively, although these values are close to those of three other indices. However, in the cities of Foumban, Ngaoundéré and Garoua, representing the western highlands, the high Guinea savannah and the Sudano-sahelian zones where built-up is more confused with soil features, overall accuracies of 97.06%, 95.29% and 74.86%, corresponding to 0.918, 0.89 and 0.42 kappa coefficients were recorded. Difference of accuracy with EBBI, NDBI and UI are up to 31.66%, confirming the NDBSUI efficiency to automate built-up extraction and unmixing from surrounding noises with less biases.

scholarly journals A conceptual model of cyclical glacier flow in overdeepenings

2014 ◽  
Vol 8 (4) ◽  
pp. 4463-4495 ◽  
Author(s):  
J. B. Turrin ◽  
R. R. Forster
Keyword(s):  
Conceptual Model ◽  
The Other ◽  
Acceleration Phase ◽  
Alaska Range ◽  
Deceleration Phase ◽  
Surface Slopes ◽  
Glacier Dynamics ◽  
Major Tributary ◽  
Cyclical Behavior ◽  
Glacier Flow

Abstract. A nearly four-decade, satellite-based velocity survey of the largest glaciers in the Alaska Range, Chugach Mountains, and the Wrangell Mountains of southern Alaska, spanning the early- to mid-1970s through the 2000s, reveals nine pulsing glaciers: Capps, Copper, Eldridge, Kahiltna, Matanuska, Nabesna, Nizina, Ruth, and Sanford glaciers. The pulses increase velocity by up to 2449% (Capps Glacier) or as little as 77% (Nabesna Glacier), with velocity increases for the other glaciers in the range of 100–250%. The pulses may last from between six years (Copper Glacier) to 12 years (Nizina Glacier) and consist of a multi-year acceleration phase followed by a multi-year deceleration phase during which significant portions of each glacier move en masse. The segments of each glacier affected by the pulses may be anywhere from 14 km (Sanford Glacier) to 36 km (Nabesna Glacier) in length and occur where the glaciers are either laterally constricted or joined by a major tributary, and the surface slopes at these locations are very shallow, 1–2°, suggesting the pulses occur where the glaciers are overdeepened. A conceptual model to explain the cyclical behavior of these pulsing glaciers is presented that incorporates the effects of glaciohydraulic supercooling, glacier dynamics, surface ablation, and subglacial sediment erosion, deposition, and deformation in overdeepenings.

scholarly journals Present dynamics and future prognosis of a slowly surging glacier

2011 ◽  
Vol 5 (1) ◽  
pp. 299-313 ◽  
Author(s):  
G. E. Flowers ◽  
N. Roux ◽  
S. Pimentel ◽  
C. G. Schoof
Keyword(s):  
Mass Balance ◽  
Force Balance ◽  
Surface Velocity ◽  
Internal Dynamic ◽  
Ice Dynamics ◽  
Surface Mass ◽  
Ice Surface ◽  
Glacier Ice ◽  
Glacier Flow ◽  
Negative Balance

Abstract. Glacier surges are a well-known example of an internal dynamic oscillation whose occurrence is not a direct response to the external climate forcing, but whose character (i.e. period, amplitude, mechanism) may depend on the glacier's environmental or climate setting. We examine the dynamics of a small (∼5 km2) valley glacier in Yukon, Canada, where two previous surges have been photographically documented and an unusually slow surge is currently underway. To characterize the dynamics of the present surge, and to speculate on the future of this glacier, we employ a higher-order flowband model of ice dynamics with a regularized Coulomb-friction sliding law in both diagnostic and prognostic simulations. Diagnostic (force balance) calculations capture the measured ice-surface velocity profile only when non-zero basal water pressures are prescribed over the central region of the glacier, coincident with where evidence of the surge has been identified. This leads to sliding accounting for 50–100% of the total surface motion in this region. Prognostic simulations, where the glacier geometry evolves in response to a prescribed surface mass balance, reveal a significant role played by a bedrock ridge beneath the current equilibrium line of the glacier. Ice thickening occurs above the ridge in our simulations, until the net mass balance reaches sufficiently negative values. We suggest that the bedrock ridge may contribute to the propensity for surges in this glacier by promoting the development of the reservoir area during quiescence, and may permit surges to occur under more negative balance conditions than would otherwise be possible. Collectively, these results corroborate our interpretation of the current glacier flow regime as indicative of a slow surge that has been ongoing for some time, and support a relationship between surge incidence or character and the net mass balance. Our results also highlight the importance of glacier bed topography in controlling ice dynamics, as observed in many other glacier systems.

scholarly journals Basal-flow characteristics of a non-linear flow sliding frictionless over strongly undulating bedrock

1997 ◽  
Vol 43 (143) ◽  
pp. 80-89 ◽  
Author(s):  
G. Hilmar Gudmundsson
Keyword(s):  
Flow Parameter ◽  
Flow Characteristics ◽  
Critical Value ◽  
Main Flow ◽  
Sliding Velocity ◽  
Flow Circulation ◽  
The Mean ◽  
Glacier Flow ◽  
Basal Shear ◽  
Basal Flow

AbstractThe flow field of a medium sliding without friction over a strongly undulating surface is calculated numerically. The results are used to elucidate the basal-flow characteristics of glacier flow and they are discussed with reference to known analytical solutions. Extrusion flow is found to become increasingly pronounced as the value of n, where n is a parameter in Glen’s flow law, becomes larger. For sinusoidal bedrock undulations, a flow separation occurs if the amplitude-to-wavelength ratio exceeds a critical value of about 0.28. The main flow then sets up a secondary flow circulation within the trough, and the ice participating in this circular motion theoretically never leaves it. The sliding velocity is calculated numerically as a function of the mean basal shear stress, the amplitude-to-wavelength ratio and the flow parameter n. For moderate and high slope fluctuations, the sliding velocity is significantly different from what would be expected from results based on the small-slope approximation.

scholarly journals Changes in the Behaviour of the Unteraargletscher in the Last 125 Years

1970 ◽  
Vol 9 (56) ◽  
pp. 195-212 ◽  
Author(s):  
R. Haefeli
Keyword(s):  
Marked Decrease ◽  
Decisive Role ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Surface Slope ◽  
Simple Method ◽  
Glacier Tongue ◽  
Slowing Down ◽  
Shear Component ◽  
Glacier Flow

All the measurements involved concern the glacier tongue between its end and 2 600 m a.s.l. The total loss of volume of the Unteraargletscher since its last maximum advance (1871) is estimated to be 2.4 km3, which corresponds to a mean surface lowering of 0.67 m/year (referred to a total glacierized area of c. 40 km2 on average). The considerable slowing down of the glacier flow velocity over the 125 years is primarily attributable to the marked decrease in the sliding component, whereas the shear component has only changed slightly. This behaviour is connected with the fact that the decrease in ice thickness has been accompanied by an increase in surface slope, so that the two effects on the shear component partially compensate each other. The seasonal variations in surface velocity were measured simultaneously at two profiles by Agassiz and his team in 1845/46. These variations are due to the variable amount of melt water and the resulting variations in hydrostatic pressure in the contact zone between ice and bedrock, in which the plastic contraction of the water channels plays a decisive role. This leads to the problem of water circulation in the interior of a glacier and its importance in the sliding process. Finally a simple method for the approximate calculation of the longitudinal profile of the surface of a glacier tongue in a steady state and with constant ablation is indicated.

scholarly journals Changes in the Behaviour of the Unteraargletscher in the Last 125 Years

1970 ◽  
Vol 9 (56) ◽  
pp. 195-212 ◽  
Author(s):  
R. Haefeli
Keyword(s):  
Marked Decrease ◽  
Decisive Role ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Surface Slope ◽  
Simple Method ◽  
Glacier Tongue ◽  
Slowing Down ◽  
Shear Component ◽  
Glacier Flow

All the measurements involved concern the glacier tongue between its end and 2 600 m a.s.l. The total loss of volume of the Unteraargletscher since its last maximum advance (1871) is estimated to be 2.4 km3, which corresponds to a mean surface lowering of 0.67 m/year (referred to a total glacierized area ofc. 40 km2on average). The considerable slowing down of the glacier flow velocity over the 125 years is primarily attributable to the marked decrease in the sliding component, whereas the shear component has only changed slightly. This behaviour is connected with the fact that the decrease in ice thickness has been accompanied by an increase in surface slope, so that the two effects on the shear component partially compensate each other. The seasonal variations in surface velocity were measured simultaneously at two profiles by Agassiz and his team in 1845/46. These variations are due to the variable amount of melt water and the resulting variations in hydrostatic pressure in the contact zone between ice and bedrock, in which the plastic contraction of the water channels plays a decisive role. This leads to the problem of water circulation in the interior of a glacier and its importance in the sliding process. Finally a simple method for the approximate calculation of the longitudinal profile of the surface of a glacier tongue in a steady state and with constant ablation is indicated.

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