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.

scholarly journals Debris cover and the thinning of Kennicott Glacier, Alaska, Part C: feedbacks between melt, ice dynamics, and surface processes

2019 ◽  
Author(s):  
Leif S. Anderson ◽  
William H. Armstrong ◽  
Robert S. Anderson ◽  
Pascal Buri
Keyword(s):  
Mass Balance ◽  
Lower Limb ◽  
Surface Velocity ◽  
Glacier Surface ◽  
Ice Dynamics ◽  
Part C ◽  
High Resolution Imagery ◽  
Debris Cover ◽  
Process Domains

Abstract. The mass balance of many valley glaciers is enhanced by the presence of melt hotspots within otherwise continuous debris cover. We assess the effect of debris, melt hotspots, and ice dynamics on the thinning of Kennicott Glacier in three companion papers. In Part A we report in situ measurements from the debris-covered tongue. In Part B, we develop a method to delineate ice cliffs using high-resolution imagery and produce distributed mass balance estimates. Here in Part C we describe feedbacks controlling rapid thinning under thick debris. Despite the extreme abundance of ice cliffs on Kennicott Glacier, average melt rates are strongly suppressed downglacier due to thick debris. The estimated melt pattern therefore appears to reflect Østrem’s curve (the debris thickness-melt relationship). As Kennicott Glacier has thinned over the last century Østrem’s curve has manifested itself in two process domains on the glacier surface. The portion of the glacier affected by the upper-limb of Østrem’s curve corresponds to high melt, melt gradients, and ice dynamics, as well as high ice cliff and stream occurrence. The portion of the glacier affected by the lower-limb of Østrem’s curve corresponds to low melt, melt gradients, and ice dynamics, as well as high ice cliff and stream occurrence. The upglacier end of the zone of maximum thinning on Kennicott Glacier occurs at the boundary between these process domains and the bend in Østrem’s curve. The expansion of debris upglacier appears to be linked to changes in the surface velocity pattern through time. In response to climate warming, debris itself may therefore control where rapid thinning occurs on debris-covered glaciers. Ice cliffs are most abundant at the upglacier end of the zone of maximum thinning.

scholarly journals Debris cover and the thinning of Kennicott Glacier, Alaska, Part A:in situ mass balance measurements

2019 ◽  
Author(s):  
Leif S. Anderson ◽  
Robert S. Anderson ◽  
Pascal Buri ◽  
William H. Armstrong
Keyword(s):  
Mass Balance ◽  
High Mountain ◽  
Glacier Surface ◽  
Ice Dynamics ◽  
Air Temperatures ◽  
High Resolution Imagery ◽  
Debris Cover ◽  
The Alps

Abstract. The mass balance of many Alaskan glaciers is perturbed by debris cover. Yet the effect of debris on glacier response to climate change in Alaska has largely been overlooked. In three companion papers we assess the role of debris, ice dynamics, and surface processes in thinning Kennicott Glacier. In Part A, we report in situ measurements from the glacier surface. In Part B, we develop a method to delineate ice cliffs using high-resolution imagery and produce distributed mass balance estimates. In Part C we explore feedbacks that contribute to glacier thinning. Here in Part A, we describe data collected in the summer of 2011. We measured debris thickness (109 locations), sub-debris melt (74), and ice cliff backwasting (60) data from the debris-covered tongue. We also measured air-temperature (3 locations) and internal-debris temperature (10). The mean debris thermal conductivity was 1.06 W (m C)−1, increasing non-linearly with debris thickness. Mean debris thicknesses increase toward the terminus and margin where surface velocities are low. Despite the relatively high air temperatures above thick debris, the melt-insulating effect of debris dominates. Sub-debris melt rates ranged from 6.5 cm d−1 where debris is thin to 1.25 cm d−1 where debris is thick near the terminus. Ice cliff backwasting rates varied from 3 to 14 cm d−1 with a mean of 7.1 cm d−1 and tended to increase as elevation declined and debris thickness increased. Ice cliff backwasting rates are similar to those measured on debris-covered glaciers in High Mountain Asia and the Alps.

scholarly journals Understanding oxide degradation mechanisms in ultra-thin SiO2 through high-speed, high-resolution in-situ measurements

2005 ◽  
Vol 80 ◽  
pp. 182-185 ◽  
Author(s):  
S. Aresu ◽  
W. De Ceuninck ◽  
R. Degraeve ◽  
B. Kaczer ◽  
G. Knuyt ◽  
...  
Keyword(s):  
High Resolution ◽  
High Speed ◽  
In Situ Measurements ◽  
Degradation Mechanisms ◽  
Oxide Degradation

scholarly journals Monitoring glacier albedo as a proxy to derive summer and annual surface mass balances from optical remote-sensing data

2018 ◽  
Vol 12 (1) ◽  
pp. 271-286 ◽  
Author(s):  
Lucas Davaze ◽  
Antoine Rabatel ◽  
Yves Arnaud ◽  
Pascal Sirguey ◽  
Delphine Six ◽  
...  
Keyword(s):  
Mass Balance ◽  
Surface Albedo ◽  
In Situ Measurements ◽  
Surface Mass Balance ◽  
Mass Balances ◽  
Equilibrium Line Altitude ◽  
Surface Mass ◽  
Minimum Surface ◽  
Summer Minimum

Abstract. Less than 0.25 % of the 250 000 glaciers inventoried in the Randolph Glacier Inventory (RGI V.5) are currently monitored with in situ measurements of surface mass balance. Increasing this archive is very challenging, especially using time-consuming methods based on in situ measurements, and complementary methods are required to quantify the surface mass balance of unmonitored glaciers. The current study relies on the so-called albedo method, based on the analysis of albedo maps retrieved from optical satellite imagery acquired since 2000 by the MODIS sensor, on board the TERRA satellite. Recent studies revealed substantial relationships between summer minimum glacier-wide surface albedo and annual surface mass balance, because this minimum surface albedo is directly related to the accumulation–area ratio and the equilibrium-line altitude. On the basis of 30 glaciers located in the French Alps where annual surface mass balance data are available, our study conducted on the period 2000–2015 confirms the robustness and reliability of the relationship between the summer minimum surface albedo and the annual surface mass balance. For the ablation season, the integrated summer surface albedo is significantly correlated with the summer surface mass balance of the six glaciers seasonally monitored. These results are promising to monitor both annual and summer glacier-wide surface mass balances of individual glaciers at a regional scale using optical satellite images. A sensitivity study on the computed cloud masks revealed a high confidence in the retrieved albedo maps, restricting the number of omission errors. Albedo retrieval artifacts have been detected for topographically incised glaciers, highlighting limitations in the shadow correction algorithm, although inter-annual comparisons are not affected by systematic errors.

Enhancing WRF Model Forecasts by Assimilating High-Resolution GPS-Derived Water-Vapor Maps combined with METEOSAT-11 Data 

2021 ◽  
Author(s):  
Yuval Reuveni ◽  
Anton Leontiev ◽  
Dorita Rostkier-Edelstein
Keyword(s):  
Water Vapor ◽  
High Resolution ◽  
Numerical Models ◽  
Eastern Mediterranean ◽  
Wrf Model ◽  
In Situ Measurements ◽  
Suggested Approach ◽  
Positioning Systems ◽  
The Mediterranean

<p>Improving the accuracy of numerical weather predictions still poses a challenging task. The lack of sufficiently detailed spatio-temporal real-time in-situ measurements constitutes a crucial gap concerning the adequate representation of atmospheric moisture fields, such as water vapor, which are critical for improving weather predictions accuracy. Information on total vertically integrated water vapor (IWV), extracted from global positioning systems (GPS) tropospheric path delays, can enhance various atmospheric models at global, regional, and local scales. Currently, numerous existing atmospheric numerical models predict IWV. Nevertheless, they do not provide accurate estimations compared with in-situ measurements such as radiosondes. In this work, we demonstrate a novel approach for assimilating 2D IWV regional maps estimations, extracted from GPS tropospheric path delays combined with METEOSAT satellite imagery data, to enhance Weather Research and Forecast (WRF) model predictions accuracy above the Eastern Mediterranean area. Unlike previous studies, which assimilated IWV point measurements, here, we assimilate quasi-continuous 2D GPS IWV maps, augmented by METEOSAT-11 data, over Israel and its surroundings. Using the suggested approach, our results show a decrease of more than 30% in the root mean square error (RMSE) of WRF forecasts after assimilation relative to the standalone WRF when verified against in-situ radiosonde measurements near the Mediterranean coast. Furthermore, substantial improvements along the Jordan Rift Valley and Dead Sea Valley areas are achieved when compared to 2D IWV regional maps. Improvements in these areas suggest the importance of the assimilated high resolution IWV maps, in particular when assimilation and initialization times coincide with the Mediterranean Sea Breeze propagation from the coastline to highland stations.</p>

A Linear Array of Wind and Pressure Sensors for High Resolution in situ Measurements in Winter Tornadoes

2016 ◽  
Vol 136 (5) ◽  
pp. 286-290
Author(s):  
Kenichi Kusunoki ◽  
Ken-ichiro Arai ◽  
Ryohei Kato ◽  
Eiichi Sato ◽  
Chusei Fujiwara
Keyword(s):  
High Resolution ◽  
Linear Array ◽  
Pressure Sensors ◽  
In Situ Measurements

scholarly journals Towards Estimating Land Evaporation at Field Scales Using GLEAM

2018 ◽  
Vol 10 (11) ◽  
pp. 1720 ◽  
Author(s):  
Brecht Martens ◽  
Richard de Jeu ◽  
Niko Verhoest ◽  
Hanneke Schuurmans ◽  
Jonne Kleijer ◽  
...  
Keyword(s):  
Water Management ◽  
Soil Moisture ◽  
High Resolution ◽  
The Netherlands ◽  
Weather Conditions ◽  
Irrigation Scheduling ◽  
In Situ Measurements ◽  
Rainfall Interception ◽  
Interception Loss

The evaporation of water from land into the atmosphere is a key component of the hydrological cycle. Accurate estimates of this flux are essential for proper water management and irrigation scheduling. However, continuous and qualitative information on land evaporation is currently not available at the required spatio-temporal scales for agricultural applications and regional-scale water management. Here, we apply the Global Land Evaporation Amsterdam Model (GLEAM) at 100 m spatial resolution and daily time steps to provide estimates of land evaporation over The Netherlands, Flanders, and western Germany for the period 2013–2017. By making extensive use of microwave-based geophysical observations, we are able to provide data under all weather conditions. The soil moisture estimates from GLEAM at high resolution compare well with in situ measurements of surface soil moisture, resulting in a median temporal correlation coefficient of 0.76 across 29 sites. Estimates of terrestrial evaporation are also evaluated using in situ eddy-covariance measurements from five sites, and compared to estimates from the coarse-scale GLEAM v3.2b, land evaporation from the Satellite Application Facility on Land Surface Analysis (LSA-SAF), and reference grass evaporation based on Makkink’s equation. All datasets compare similarly with in situ measurements and differences in the temporal statistics are small, with correlation coefficients against in situ data ranging from 0.65 to 0.95, depending on the site. Evaporation estimates from GLEAM-HR are typically bounded by the high values of the Makkink evaporation and the low values from LSA-SAF. While GLEAM-HR and LSA-SAF show the highest spatial detail, their geographical patterns diverge strongly due to differences in model assumptions, model parameterizations, and forcing data. The separate consideration of rainfall interception loss by tall vegetation in GLEAM-HR is a key cause of this divergence: while LSA-SAF reports maximum annual evaporation volumes in the Green Heart of The Netherlands, an area dominated by shrubs and grasses, GLEAM-HR shows its maximum in the national parks of the Veluwe and Heuvelrug, both densely-forested regions where rainfall interception loss is a dominant process. The pioneering dataset presented here is unique in that it provides observational-based estimates at high resolution under all weather conditions, and represents a viable alternative to traditional visible and infrared models to retrieve evaporation at field scales.

Implementing an object-based multi-index protocol for mapping surface glacier facies from Chandra-Bhaga basin, Himalaya

2019 ◽  
Vol 9 (2) ◽  
pp. 125-140
Author(s):  
Shridhar Digambar Jawak ◽  
Sagar Filipe Wankhede ◽  
Alvarinho Joaozinho Luis ◽  
Prashant Hemendra Pandit ◽  
Shubhang Kumar
Keyword(s):  
High Resolution ◽  
Mass Balance ◽  
Structural Characteristics ◽  
Multi Index ◽  
Spectral Bands ◽  
High Resolution Imagery ◽  
Object Based ◽  
Band Ratioing ◽  
Very High Resolution Imagery ◽  
Very High

Surface glacier facies are superficial expressions of a glacier that are distinguishable based on differing spectral and structural characteristics according to their age and inter-mixed impurities. Increasing bodies of literature suggest that the varying properties of surface glacier facies differentially influence the melt of the glacier, thus affecting the mass balance. Incorporating these variations into distributed mass balance modelling can improve the perceived accuracy of these models. However, detecting and subsequently mapping these facies with a high degree of accuracy is a necessary precursor to such complex modelling. The variations in the reflectance spectra of various glacier facies permit multiband imagery to exploit band ratios for their effective extraction. However, coarse and medium spatial resolution multispectral imagery can delimit the efficacy of band ratioing by muddling the minor spatial and spectral variations of a glacier. Very high-resolution imagery, on the other hand, creates distortions in the conventionally obtained information extracted through pixel-based classification. Therefore, robust and adaptable methods coupled with higher resolution data products are necessary to effectively map glacier facies. This study endeavours to identify and isolate glacier facies on two unnamed glaciers in the Chandra-Bhaga basin, Himalayas, using an established object-based multi-index protocol. Exploiting the very high resolution offered by WorldView-2 and its eight spectral bands, this study implements customized spectral index ratios via an object-based environment. Pixel-based supervised classification is also performed using three popular classifiers to comparatively gauge the classification accuracies. The object-based multi-index protocol delivered the highest overall accuracy of 86.67%. The Minimum Distance classifier yielded the lowest overall accuracy of 62.50%, whereas, the Mahalanobis Distance and Maximum Likelihood classifiers yielded overall accuracies of 77.50% and 70.84% respectively. The results outline the superiority of the object-based method for extraction of glacier facies. Forthcoming studies must refine the indices and test their applicability in wide ranging scenarios.

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