scholarly journals Stagnation of the Pensilungpa glacier, western Himalaya, India: causes and implications

2021 ◽  
pp. 1-15
Author(s):  
Purushottam Kumar Garg ◽  
Siddhi Garg ◽  
Bisma Yousuf ◽  
Aparna Shukla ◽  
Vinit Kumar ◽  
...  
Keyword(s):  
High Resolution ◽  
Field Measurements ◽  
Western Himalaya ◽  
Ablation Zone ◽  
Ablation Process ◽  
Current State ◽  
High Resolution Imagery ◽  
Debris Cover ◽  
Previous Decade ◽  
Srtm Data

Abstract This study investigates stagnation conditions of the Pensilungpa glacier, western Himalaya. Multiple glacier parameters (length, area, debris extent and thickness, snowline altitude (SLA), velocity, downwasting and ice cliffs) were studied using field measurements (2016–18), high-resolution imagery from GoogleEarth (2013–17) and spaceborne Landsat, ASTER and SRTM data (1993–2017) to comprehend the glacier's current state. Results show a moderate decrease in length (6.62 ± 2.11 m a−1) and area (0.11 ± 0.03% a−1), a marked increase in SLA (~6 m a−1) and debris cover (2.86 ± 0.29% a−1) and a slowdown of ~50% during 1993–2016. Notable thinning of −0.88 ± 0.04 m a−1 was observed between 2000 and 2017 showing a similar trend as field measurements during 2016–17 (−0.88 m) and 2017–18 (−1.54 m). Further, results reveal a stagnation of the lower ablation zone (LAZ). Less mass supply and heterogeneous debris growth (6.67 ± 0.41% a−1) over the previous decade resulted in slowdown, margin insulation and slope-inversion, leading to stagnation. Stagnation of LAZ caused bulging in the dynamic upper ablation zone and favored the development of supraglacial ponds and ice cliffs. Ice cliffs have grown significantly (48% in number; 41% in area during 2013–17) and their back-wasting now dominates the ablation process.

Debris cover growth, ensuing changes in morphology and impact on glacier processes at Pensilungpa Glacier, western Himalaya, India

2020 ◽  
Author(s):  
Purushottam Kumar Garg ◽  
Aparna Shukla ◽  
Vinit Kumar ◽  
Manish Mehta
Keyword(s):  
Thickness Distribution ◽  
Field Measurements ◽  
Western Himalaya ◽  
Rapid Expansion ◽  
Ablation Zone ◽  
Multiple Parameters ◽  
Low Area ◽  
Area Loss ◽  
Recent Estimate ◽  
Debris Cover

<p>Supraglacial debris affects the melting processes and overall response of glaciers to climate change. The present study investigates the temporal variation in debris cover and its influence on the overall state of the Pensilungpa glacier (14.67 ±0.29 km<sup>2</sup>), western Himalaya, India, which has extensive debris on its lower ablation zone (LAZ). For this, multiple parameters namely length, area, debris extent/thickness, snowline altitude (SLA), surface ice velocity (SIV), surface elevation changes and ice-cliffs were determined using field measurements (2016-2018), GoogleEarth images (2013-2017) and satellite data (Landsat-TM/ETM+/OLI (1993-2017), SRTM (2000) and Terra-ASTER (2017)) to comprehend the past and present status of the glacier. Results show a moderate terminus retreat (6.62 ±2.11 m/y) and area loss (0.11 ±0.03%/y) but a marked slowdown (~50%) in the glacier supported by significant SLA upshift (~6 m/y) during 1993-2017. Geodetic measurements reveal a prominent downwasting of −0.88 ±0.04 m/y during 2000-2017 which is corroborated with ablation-stake measurements that show average annual melting of −0.88 m during 2016-2017 and −1.54 m during 2017-2018. The glacier moved with a slow velocity of 13.94 ±3.94 m/y in 1993/94 and its velocity further slowed-down to 9.33 ±2.76 m/y in 1999/2000 and to 7.63 ±3.87 m/y in 2016/17 revealing a slow-down of 1.97%/y. Notably, the magnitude of change in most glacier parameters was lower in the recent period (2000-2017) as compared to the previous one (1993-2000). The observed SLA upshift (180 m), area loss (0.17 ±0.24%/y) and slowdown rates (4.73%/y) were much higher during 1993-2000. Contrarily, the glacier experienced a low area loss (0.09 ±0.09%/y), slowdown (1.14%/y) and even descend in SLA (43 m) between 2000 and 2017. The overall glacier depletion has resulted in substantial debris cover increase of 2.86 ±0.29%/y during the study period (1993-2017). Following the glacier depletion trend, the debris growth rate was also much higher (6.67 ±0.41%/y) during 1993-2000 and reduced (to 0.81 ±0.12%/y) subsequently (2000-2017). The most recent estimate (2016) shows a total debris cover of 17.35% on the Pensilungpa glacier and field measurements show that the debris tends to be thicker towards the margins. Such a setting probably insulated the glacier margins which, coupled with steady slowdown, has caused the stagnation of the LAZ up to 2 km upstream, which is reflected in SIV results and temporal GoogleEarth images. Also, the debris thickness distribution on glacier is such that it is thicker near the snout (>40 cm) and gradually decreases upstream (<2 cm at ~2.5 km). This has caused differential melting by insulating-effect and albedo lowering-effect and has promoted slope inversion, contributing further to stagnation. Stagnation of the LAZ has caused bulging in the dynamically active upper ablation zone and favored the development of supraglacial lakes (5 in 2017) and numerous ice-cliffs (79 in 2017). In view of insulated margins, back-wasting of ice-cliffs dominates the ablation process which is evident by rapid expansion in their number (48%), perimeter (31%) and area (41%) during 2013-2017. To conclude, the debris cover has significantly altered multiple glacier processes and has largely controlled the glacier evolution.</p>

scholarly journals Debris cover and the thinning of Kennicott Glacier, Alaska, Part B: ice cliff delineation and distributed melt estimates

2019 ◽  
Author(s):  
Leif S. Anderson ◽  
William H. Armstrong ◽  
Robert S. Anderson ◽  
Pascal Buri
Keyword(s):  
High Resolution ◽  
Mass Balance ◽  
In Situ Measurements ◽  
Empirical Relationships ◽  
Full Extent ◽  
Part C ◽  
Important Contributor ◽  
High Resolution Imagery ◽  
Debris Cover

Abstract. The mass balance of many valley glaciers is enhanced by the presence of ice cliffs within otherwise continuous debris cover. We assess the effect of debris and ice cliffs on the thinning of Kennicott Glacier in three companion papers. In Part A we report in situ measurements from the debris-covered tongue. Here, in Part B, we develop a method to delineate ice cliffs using high-resolution imagery and use empirical relationships from Part A to produce distributed mass balance estimates. In Part C we describe feedbacks that contribute to rapid thinning under thick debris. Ice cliffs cover 11.7 % of the debris-covered tongue, the most of any glacier studied to date, and they contribute 19 % of total melt. Ice cliffs contribute an increasing percentage of melt the thicker the debris cover. In the lowest 4 km of the glacier, where debris thicknesses are greater than 20 cm, ice cliffs contribute 40 % of total melt. Surface lake coverage doubled between 1957 and 2009, but lakes do not occur across the full extent of the zone of maximum glacier thinning. Despite abundant ice cliffs and expanding surface lakes, average melt rates are suppressed by debris, the pattern of which appears to reflect the debris thickness-melt relationship (or Østrem’s curve). This suggests that, in addition to melt hotspots, the decline in ice discharge from upglacier is an important contributor to the thinning of Kennicott glacier under thick debris.

Capability of the CANAPI algorithm to derive shrub structural parameters from satellite imagery in the Alaskan Arctic

Polar Record ◽  
2015 ◽  
Vol 52 (2) ◽  
pp. 124-133 ◽  
Author(s):  
Rocio R. Duchesne ◽  
Mark J. Chopping ◽  
Ken D. Tape
Keyword(s):  
High Resolution ◽  
Structural Parameters ◽  
Image Interpretation ◽  
Field Measurements ◽  
Structural Data ◽  
The Arctic ◽  
Regression Equations ◽  
Fractional Cover ◽  
High Resolution Imagery ◽  
Tundra Ecosystem

ABSTRACTThe observed greening of Arctic vegetation and the expansion of shrubs in the last few decades probably have profound implications for the tundra ecosystem, including feedbacks to climate. Uncertainty surrounding this vegetation shift and its implications calls for monitoring of vegetation structural parameters, such as fractional cover of shrubs. In this study, CANAPI, a semi-automated image interpretation algorithm that identifies and traces crowns by locating its crescent-shaped sunlit portion, was evaluated for its ability to derive structural data for tall (> 0.5 m) shrubs in the Arctic. CANAPI estimates of shrub canopy parameters were obtained from high-resolution imagery at 26 sites (250 m x 250 m each) by adjusting the algorithm's parameters and filter settings for each site, such that the number of crowns delineated by CANAPI roughly matched those observed in the high-resolution imagery. The CANAPI estimates were then compared with field measurements to evaluate the algorithm's performance. CANAPI successfully retrieved fractional cover (R2= 0.83,P< 0.001), mean crown radius (R2= 0.81,P< 0.001), and total number of shrubs (R2= 0.54,P< 0.001). CANAPI performed best in sparse vegetation where shrub canopies were distinct, while it tended to underestimate shrub cover where shrubs were clustered. The CANAPI algorithm and the regression equations presented here can be used in Arctic tundra environments to derive vegetation parameters from any sub-meter panchromatic imagery.

Recent applications of TEM to the study of interfaces

1990 ◽  
Vol 48 (4) ◽  
pp. 308-309
Author(s):  
C. Barry Carter
Keyword(s):  
High Resolution ◽  
Sample Preparation ◽  
Grain Boundaries ◽  
Diffuse Scattering ◽  
Imaging Techniques ◽  
Amorphous Material ◽  
Contrast Imaging ◽  
Current State ◽  
Actual Nature ◽  
High Resolution Images

This paper will review the current state of understanding of interface structure and highlight some of the future needs and problems which must be overcome. The study of this subject can be separated into three different topics: 1) the fundamental electron microscopy aspects, 2) material-specific features of the study and 3) the characteristics of the particular interfaces. The two topics which are relevant to most studies are the choice of imaging techniques and sample preparation. The techniques used to study interfaces in the TEM include high-resolution imaging, conventional diffraction-contrast imaging, and phase-contrast imaging (Fresnel fringe images, diffuse scattering). The material studied affects not only the characteristics of the interfaces (through changes in bonding, etc.) but also the method used for sample preparation which may in turn have a significant affect on the resulting image. Finally, the actual nature and geometry of the interface must be considered. For example, it has become increasingly clear that the plane of the interface is particularly important whenever at least one of the adjoining grains is crystalline.A particularly productive approach to the study of interfaces is to combine different imaging techniques as illustrated in the study of grain boundaries in alumina. In this case, the conventional imaging approach showed that most grain boundaries in ion-thinned samples are grooved at the grain boundary although the extent of this grooving clearly depends on the crystallography of the surface. The use of diffuse scattering (from amorphous regions) gives invaluable information here since it can be used to confirm directly that surface grooving does occur and that the grooves can fill with amorphous material during sample preparation (see Fig. 1). Extensive use of image simulation has shown that, although information concerning the interface can be obtained from Fresnel-fringe images, the introduction of artifacts through sample preparation cannot be lightly ignored. The Fresnel-fringe simulation has been carried out using a commercial multislice program (TEMPAS) which was intended for simulation of high-resolution images.

Mapping and Monitoring of the Land Use/Cover Changes in the Wider Area of ltanos, Crete, Using Very High Resolution EO Imagery With Specific Interest in Archaeological Sites

2019 ◽  
Author(s):  
Sawyer Reid stippa ◽  
George Petropoulos ◽  
Leonidas Toulios ◽  
Prashant K. Srivastava
Keyword(s):  
High Resolution ◽  
Spatial Resolution ◽  
Satellite Images ◽  
Archaeological Site ◽  
Digital Photography ◽  
Archaeological Sites ◽  
Large Area ◽  
High Resolution Imagery ◽  
Site Mapping ◽  
Rule Sets

Archaeological site mapping is important for both understanding the history as well as protecting them from excavation during the developmental activities. As archaeological sites generally spread over a large area, use of high spatial resolution remote sensing imagery is becoming increasingly applicable in the world. The main objective of this study was to map the land cover of the Itanos area of Crete and of its changes, with specific focus on the detection of the landscape’s archaeological features. Six satellite images were acquired from the Pleiades and WorldView-2 satellites over a period of 3 years. In addition, digital photography of two known archaeological sites was used for validation. An Object Based Image Analysis (OBIA) classification was subsequently developed using the five acquired satellite images. Two rule-sets were created, one using the standard four bands which both satellites have and another for the two WorldView-2 images their four extra bands included. Validation of the thematic maps produced from the classification scenarios confirmed a difference in accuracy amongst the five images. Comparing the results of a 4-band rule-set versus the 8-band showed a slight increase in classification accuracy using extra bands. The resultant classifications showed a good level of accuracy exceeding 70%. Yet, separating the archaeological sites from the open spaces with little or no vegetation proved challenging. This was mainly due to the high spectral similarity between rocks and the archaeological ruins. The satellite data spatial resolution allowed for the accuracy in defining larger archaeological sites, but still was a difficulty in distinguishing smaller areas of interest. The digital photography data provided a very good 3D representation for the archaeological sites, assisting as well in validating the satellite-derived classification maps. All in all, our study provided further evidence that use of high resolution imagery may allow for archaeological sites to be located, but only where they are of a suitable size archaeological features.

ASSESSING MICROFOSSIL TAPHONOMY WITH HIGH-RESOLUTION IMAGERY

2017 ◽  
Author(s):  
R. Seth Wood ◽  
◽  
Ashley R. Manning-Berg ◽  
Kenneth H. Williford ◽  
Linda C. Kah
Keyword(s):  
High Resolution ◽  
High Resolution Imagery

scholarly journals Assessing Riyadh’s Urban Change Utilizing High-Resolution Imagery

Land ◽  
2019 ◽  
Vol 8 (12) ◽  
pp. 193
Author(s):  
Ali Alghamdi ◽  
Anthony R. Cummings
Keyword(s):  
Maximum Likelihood ◽  
High Resolution ◽  
Accuracy Assessment ◽  
Middle Eastern ◽  
Object Oriented ◽  
Training Data ◽  
High Resolution Imagery ◽  
Significant Research ◽  
Desert Areas ◽  
Spot 5

The implications of change on local processes have attracted significant research interest in recent times. In urban settings, green spaces and forests have attracted much attention. Here, we present an assessment of change within the predominantly desert Middle Eastern city of Riyadh, an understudied setting. We utilized high-resolution SPOT 5 data and two classification techniques—maximum likelihood classification and object-oriented classification—to study the changes in Riyadh between 2004 and 2014. Imagery classification was completed with training data obtained from the SPOT 5 dataset, and an accuracy assessment was completed through a combination of field surveys and an application developed in ESRI Survey 123 tool. The Survey 123 tool allowed residents of Riyadh to present their views on land cover for the 2004 and 2014 imagery. Our analysis showed that soil or ‘desert’ areas were converted to roads and buildings to accommodate for Riyadh’s rapidly growing population. The object-oriented classifier provided higher overall accuracy than the maximum likelihood classifier (74.71% and 73.79% vs. 92.36% and 90.77% for 2004 and 2014). Our work provides insights into the changes within a desert environment and establishes a foundation for understanding change in this understudied setting.

scholarly journals 2nd Edition of Instrumenting Smart City Applications with Big Sensing and Earth Observatory Data: Tools, Methods and Techniques

2021 ◽  
Vol 13 (7) ◽  
pp. 1310
Author(s):  
Gabriele Bitelli ◽  
Emanuele Mandanici
Keyword(s):  
High Resolution ◽  
Exponential Growth ◽  
Smart City ◽  
Earth Observation ◽  
Urban Environments ◽  
Observation Data ◽  
High Resolution Imagery ◽  
Observatory Data ◽  
Methods And Techniques ◽  
Earth Observation Data

The exponential growth in the volume of Earth observation data and the increasing quality and availability of high-resolution imagery are increasingly making more applications possible in urban environments [...]

scholarly journals Multi-Scene Building Height Estimation Method Based on Shadow in High Resolution Imagery

2021 ◽  
Vol 13 (15) ◽  
pp. 2862
Author(s):  
Yakun Xie ◽  
Dejun Feng ◽  
Sifan Xiong ◽  
Jun Zhu ◽  
Yangge Liu
Keyword(s):  
Remote Sensing ◽  
High Resolution ◽  
Estimation Method ◽  
Absolute Error ◽  
Large Error ◽  
Estimation Methods ◽  
Height Estimation ◽  
Building Height ◽  
Remote Sensing Imagery ◽  
High Resolution Imagery

Accurately building height estimation from remote sensing imagery is an important and challenging task. However, the existing shadow-based building height estimation methods have large errors due to the complex environment in remote sensing imagery. In this paper, we propose a multi-scene building height estimation method based on shadow in high resolution imagery. First, the shadow of building is classified and described by analyzing the features of building shadow in remote sensing imagery. Second, a variety of shadow-based building height estimation models is established in different scenes. In addition, a method of shadow regularization extraction is proposed, which can solve the problem of mutual adhesion shadows in dense building areas effectively. Finally, we propose a method for shadow length calculation combines with the fish net and the pauta criterion, which means that the large error caused by the complex shape of building shadow can be avoided. Multi-scene areas are selected for experimental analysis to prove the validity of our method. The experiment results show that the accuracy rate is as high as 96% within 2 m of absolute error of our method. In addition, we compared our proposed approach with the existing methods, and the results show that the absolute error of our method are reduced by 1.24 m-3.76 m, which can achieve high-precision estimation of building height.

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