Thèses : « Glacier mass balance estimation »

1

Podsiadło, Iwona Katarzyna. « Methods for the analysis of time series of multispectral remote sensing images and application to climate change variable estimations ». Doctoral thesis, Università degli studi di Trento, 2021. http://hdl.handle.net/11572/322351.

Texte intégral

Résumé :

In the last decades, the increasing number of new generation satellite images characterized by a better spectral, spatial and temporal resolution with respect to the past has provided unprecedented source of information for monitoring climate changes.To exploit this wealth of data, powerful and automatic methods to analyze remote sensing images need to be implemented. Accordingly, the objective of this thesis is to develop advanced methods for the analysis of multitemporal multispectral remote sensing images to support climate change applications. The thesis is divided into two main parts and provides four novel contributions to the state-of-the-art. In the first part of the thesis, we exploit multitemporal and multispectral remote sensing data for accurately monitoring two essential climate variables. The first contribution presents a method to improve the estimation of the glacier mass balance provided by physically-based models. Unlike most of the literature approaches, this method integrates together physically-based models, remote sensing data and in-situ measurements to achieve an accurate and comprehensive glacier mass balance estimation. The second contribution addresses the land cover mapping for monitoring climate change at high spatial resolution. Within this work, we developed two processing chains: one for the production of a recent (2019) static high resolution (10 m) land cover map at subcontinental scale, and the other for the production of a long-term record of regional high resolution (30 m) land cover maps. The second part of this thesis addresses the common challenges faced while performing the analysis of multitemporal multispectral remote sensing data. In this context, the third contribution deals with the multispectral images cloud occlusions problem. Differently from the literature, instead of performing computationally expensive cloud restoration techniques, we study the robustness of deep learning architectures such as Long Short Term Memory classifier to cloud cover. Finally, we address the problem of the large scale training set definition for multispectral data classification. To this aim, we propose an approach that leverages on available low resolution land cover maps and domain adaptation techniques to provide representative training sets at large scale. The proposed methods have been tested on Sentinel-2 and Landsat 5, 7, 8 multispectral images. Qualitative and quantitative experimental results confirm the effectiveness of the methods proposed in this thesis.

Styles APA, Harvard, Vancouver, ISO, etc.

2

Huss, Matthias. « Past and future changes in glacier mass balance / ». Zürich : ETH, 2009. http://opac.nebis.ch/cgi-bin/showAbstract.pl?sys=000256345.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

3

Wiklund, Sara. « Long-term glacier mass balance of Nordenskiöldbreen, Svalbard ». Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-295789.

Texte intégral

Résumé :

The global warming that’s taking place have an impact over the Earth and the glaciers on Svalbard are undergoing rapid changes as a result. The annual air temperature has been rising on Svalbard since the early 1900’s and in a climate projection expected temperatures continue to rise. The glacial mass balance is important for monitoring glacier response to climate change. In this study the mass balance of Nordenskiöldbreen from 1957 to 2016 is modelled with a temperature-index model. The meteorological data used in the model, precipitation and air temperature, has been measured at a weather station located in Longyearbyen since 1957. The long simulation run makes trends in mass balance, precipitation and air temperature apparent. The mass balance can also be correlated to the temperature and precipitation, which provide important information on how these affect the behavior of glaciers. The results obtained can be used to predict how glaciers change in the future with climate change. In the simulation Nordenskiöldbreen’s mass balance has a negative trend, precipitation doesn’t have any trend and air temperature has a positive trend. The long-term mass balance is controlled by air temperature and the short-term interannual mass balance is caused by precipitation fluctuations.
Den globala uppvärmningen som sker just nu har en påverkan över hela jorden och glaciärer på Svalbard genomgår snabba förändringar som följd. På Svalbard har den årliga medeltemperaturen stigit sedan början av 1900-talet och i en klimatprojicering förväntas temperaturen att fortsätta stiga. Den glaciala massbalansen är viktig för att övervaka glaciärers respons till klimatförändringar. I detta arbete modelleras Nordenskiöldbreens massbalans från 1957 till 2016 med hjälp av en temperaturindex modell. Den meteorologiska data som används i modellen, nederbörd och temperatur, har mätts vid en väderstation i Longyearbyen sedan 1957. Med den långa tidsperioden i modellen blir långsiktiga trender i massbalans, nederbörd och temperatur tydliga. Massbalansen kan även korreleras mot temperatur och nederbörd, vilket ger viktig information om hur dessa påverkar glaciärers beteenden. De resultat som framkommer kan användas för att förutspå hur glaciärer förändras i framtiden med en klimatändring. I simuleringen har Nordenskiöldbreens massbalans en negativ trend, nederbörd har ingen trend och temperatur har en positiv trend. Det är temperatur som styr den långsiktiga massbalansen och den kortsiktiga mellanårs-massbalansen styrs av nederbörds fluktuationer.

Styles APA, Harvard, Vancouver, ISO, etc.

4

Huss, Matthias Boes Robert. « Past and future changes in glacier mass balance / ». Zürich : Versuchsanstalt für Wasserbau, Hydrologie und Glaziologie, ETH Zürich, 2009. http://opac.nebis.ch/cgi-bin/showAbstract.pl?sys=000263371.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

5

Fujita, Koji, et 耕史藤田. « Effect of precipitation seasonality on climatic sensitivity of glacier mass balance ». Elsevier, 2008. http://hdl.handle.net/2237/11360.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

6

Rye, Cameron James. « Spatially distributed modelling of regional glacier mass balance : a Svalbard case study ». Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609569.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

7

Herdes, Emilie. « Evolution of Seasonal Variations in Motion of the Kaskawulsh Glacier, Yukon Territory ». Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31835.

Texte intégral

Résumé :

Differential GPS data from 2007-2014 are used to assess horizontal and vertical velocity variations of the Kaskawulsh Glacier at interannual and intra-annual timescales. These indicate that an upglacier propagating high velocity event occurs every spring at the onset of melt, and that a downglacier propagating high velocity event occurs every fall or winter after melt has finished. These events suggest that the subglacial drainage system alternates between a distributed system in the winter and channelized system in the summer and fall. In addition, there is a strong negative correlation between summer melt and velocity the following fall and winter, with strong melt years resulting in low velocities. For each additional metre of summer melt, an 8.6% average decrease in velocity is observed on the glacier the following fall-winter. These results suggest that changes in the subglacial drainage system limit the sensitivity of glacier motion to increased meltwater inputs. Glacier motion will likely show a net decrease under a warming climate due to the negative correlation between surface melt rates and ice motion and a decrease in driving stresses as a result of reduced ice thicknesses. In addition, future fall-winter velocity patterns could be accurately predicted from only a month or two of summer melt data, with May-June melt providing the best indication of fall-winter motion. This study also suggests that the common assumption that glaciers are ‘stable’ in the late fall and winter is incorrect.

Styles APA, Harvard, Vancouver, ISO, etc.

8

Kilic, Lise. « Estimation des paramètres de surface des océans et de la banquise à partir d’observations micro-ondes basses fréquences ». Electronic Thesis or Diss., Sorbonne université, 2019. http://www.theses.fr/2019SORUS167.

Texte intégral

Résumé :

Les océans et la banquise jouent un rôle important dans le système climatique et météorologique. Une future mission satellite en micro-ondes passives basses fréquences, conçue pour observer les régions polaires est actuellement à l’étude à l’Agence Spatiale Européenne pour l’expansion du programme Copernicus. Les observations satellites en micro-ondes passives permettent une observation de la surface de la Terre par tous temps, aussi bien de jour que de nuit. Dans cette thèse, nous nous intéressons à l’estimation des paramètres de surface de l’océan et de la banquise à partir des observations satellites micro-ondes passives basses fréquences. L’objectif est de développer de nouvelles méthodes d’estimation de ces paramètres qui soient plus efficaces et adaptées à la future mission satellite micro-onde passive CIMR (Copernicus Imaging Microwave Radiometer). La première partie de la thèse traite de l’estimation des paramètres océaniques tels que la température de la surface de la mer, la salinité et la vitesse du vent océanique. La deuxième partie traite de l’estimation des paramètres de la banquise tels que la concentration en glace, l’épaisseur de neige et la température d’interface neige-glace. Enfin, avec les méthodes développées dans cette thèse les performances de la mission CIMR sont évaluées et comparées à celles des missions actuelles
The oceans and sea ice play an important role in the climate and weather system. A future low-frequency passive microwave satellite mission designed to observe the polar regions is currently under study at the European Space Agency for the expansion of the Copernicus programme. Passive microwave satellite observations provide all-weather observation of the Earth surface, both day and night. In this thesis, we are interested in estimating ocean and ice surface parameters from low-frequency passive microwave satellite observations. The objective is to develop new methods for estimating these parameters that are more efficient and adapted to the future passive microwave satellite mission CIMR (Copernicus Imaging Microwave Radiometer). The first part of the thesis deals with the estimation of ocean parameters such as sea surface temperature, salinity and ocean wind speed. The second part deals with the estimation of sea ice parameters such as sea ice concentration, snow depth and snow-ice interface temperature. Finally, with the methods developed in this thesis, the performances of the CIMR mission are evaluated and compared with the current missions

Styles APA, Harvard, Vancouver, ISO, etc.

9

Bergman, Ottar. « A Regional Analysis of Changing Climate Conditions and Glacier Mass Balance in Svalbard ». Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-383930.

Texte intégral

Résumé :

The Arctic archipelago of Svalbard has experienced among the greatest increases in temperature on Earth in the last few decades. The changing climatic conditions have a large impact on the glacier mass balance. This study makes use of a highresolution model dataset with data on climatic and glacier conditions on Svalbard from 1957 to 2018. The model dataset is used to analyse the spatiotemporal variability in glacier mass balance across Svalbard and linking those changes to long-term trends in meteorological conditions. The study is focused on the spatial gradients in trends between two regions in Svalbard, the coldest part of the archipelago, Nordaustlandet and the milder southern part of the main island Spitsbergen. The north eastern (NE) region is found to have a greater increase in annual air temperature over the simulation period with 5.5 °C compared to 3.5 °C for the south western (SW) region. The increase in annual summer temperatures is much smaller with a total increase of 1 °C for the NW and 1.5 °C for the SW. Both regions show a small, but significant, increase of precipitation. Relative humidity and cloud cover in the NE are increasing slightly over the time period, probably due to retreating sea ice cover. Glacier melt and runoff are increasing in both regions, which is contributing to significant negative trends in the mass balance. The increase in melt and run off is stronger in the SW than in the NE. There’s a strong correlation between summer air temperature and glacier mass balance, melt and runoff. Refreezing in the NE is decreasing much faster than in the SW. Refreezing is strongly correlated with annual air temperatures in the NE and not in the SW, probably due to lower temperatures in the NE region.

Styles APA, Harvard, Vancouver, ISO, etc.

10

Gustavsson, Maja. « Mass Balance of the High-Arctic Glacier Nordenskiöldbreen, Svalbard, in a Changing Climate ». Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-388495.

Texte intégral

Résumé :

Melting glaciers are the major contributor to sea level rise. Glaciers are sensitive indicators of climate change and current experience strong developments in a rapidly warming Arctic environment. Time-series of the mass balance of the glacier Nordenskiöldbreen are constructed by using height observations from the stake measurements on the glacier. The connection between the glacier mass balance and monthly averaged weather parameters observed at nearby meteorological stations will be analyzed. The total net balance on glacier Nordenskiöldbreen is found to be negative (-0.09 m w.e. per year) between 2005 and 2017. The mass balance during the summer season correlates strongest with maximum air temperature, while the winter balance is found to be mostly influenced by cloud cover and temperature, rather than precipitation. The results show that precipitation observed at nearby weather stations are not representative for precipitation amounts observed on the glacier.
Glaciärer som smälter är en av de största bidragen till den förhöjda havsnivån. Det är därför viktigt att studera Svalbards glaciärer för att kunna svara på hur den arktiska uppvärmningen påverkar issystemen. En tidsserie över massbalansen för glaciären Nordenskiöldbreen skapades genom höjdobservationer från stavmätningar befintliga på glaciären. I nästa steg analyserades kopplingen mellan glaciärmassbalansen och väderparametrarna som observerats vid närliggande meteorologiska stationer. Den totala netbalansen på glaciären Nordenskiöldbreen visade sig vara negativ (-0.09 m w.e. per år) mellan år 2005 och 2017. Massbalansen under sommarsäsongen korrelerade starkast med maximal lufttemperatur medan vinterbalansen var mest påverkad av molntäcke och temperatur, snarare än nederbörd. Resultaten visar att nederbörd observerad vid närliggande väderstationer inte är representativ för nederbördsmängder observerade på glaciären.

Styles APA, Harvard, Vancouver, ISO, etc.

11

Tinder, Phaedra C. « Ocean-Ice Interactions at Breiðamerkurjökull Glacier, Southeast Iceland ». The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1339663923.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

12

Wright, Andrew Philip. « The impact of meltwater refreezing on the mass balance of a high Arctic glacier ». Thesis, University of Bristol, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435704.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

13

David, Höglin. « Regional and Local Factors Influencing the Mass Balance of the Scandinavian Glaciers ». Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-311152.

Texte intégral

Résumé :

According to climatic models there will be an increase in the amount of greenhouse gases which results in a warming of the earth where the change will be most prominent in the high latitudes. Glaciers mass balance is a good climate change indicator as the response is fast when climate is changing. Glacier mass balance, area of glaciers, elevation line altitude data for 13 glaciers in Scandinavia as well as North Atlantic oscillation (NAO), Arctic oscillation (AO) and sunspot data where gathered and a principle component analysis (PCA) where made. PCA is a multivariate statistical technique with the goal to extract important information and reduce the dimension of data. Three distinct groupings where found within the data set and was identified as extreme years of North Atlantic Oscillation and Arctic Oscillation and one glacier which had the largest area of the 13 glaciers. The PCA explained that all the variables in the data set is correlated with North Atlantic and Arctic Oscillation to about 40 % and we can conclude that there is a regional and local forcing within our data where the regional (NAO and AO) is of more importance for the variance and for the mass balance.
Enligt klimatmodeller kommer en ökning av växthusgaser i atmosfären leda till en ökning av temperaturen på jorden, den ökningen kommer främst att ske på höga latituder. Glaciärer är bra indikation på förändrat klimat på grund av deras korta responstid när klimatet ändrar sig. För tillfället finns det ca 1900 glaciärer utspridda i de Skandinaviska bergen. Eftersom Skandinavien är så avlångt är det en skillnad i meterologiska och klimatiska förhållanden, både i en nord-syd riktning men även i en öst-väst riktning med kontinentala glaciärer i öst och mer marina i väst. Klimat och glaciärdata för 13 olika glaciärer i Skandinavien, 5 från Sverige och 8 ifrån Norge har samlats in och en statistisk analys, principle component analysis (PCA) har gjorts för att se vad som påverkar massbalansen för glaciärerna. De klimat parametrar som har undersökts är Nordatlantsika oscillationen (NAO), Arktiska oscillationen (AO) och solfläckar tillsammans med massbalans, equilibrium line altitude (ELA) och area för glaciärerna. Tre grupperingar har hittats som kan kopplas till olika klimatvariabler och PCA visar extremår för NAO och AO samt en glaciär som har den största arean. PCA analysen visade att alla variabler korrelerade till NAO och AO med omkring 40 % och vi kan dra slutsatsen att det finns en drivande regional och lokal kraft inom vårat dataset där NAO och AO är viktigast för massbalansen.

Styles APA, Harvard, Vancouver, ISO, etc.

14

Thomson, Laura Irene. « Connections Between the Mass Balance, Ice Dynamics, and Hypsometry of White Glacier, Axel Heiberg Island, Nunavut ». Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35106.

Texte intégral

Résumé :

This thesis investigates how changing climate conditions have impacted the mass balance, dynamics and associated hypsometry (area-elevation distribution) of White Glacier, an alpine glacier on Axel Heiberg Island, Nunavut. The first article describes the production of a new map of White Glacier from which changes in ice thickness and glacier hypsometry could be determined. A new digital elevation model (DEM) was created using >400 oblique air photos and Structure from Motion, a method built upon photogrammetry but with the advantage of automated image correlation analysis. The result of this work demonstrates that the method is able to overcome the challenges of optical remote sensing in snow-covered areas. The resulting DEM and orthoimage facilitated the production of a map with 5 m vertical accuracy in the style of earlier cartographic works. The new map supported the calculation of the glacier’s geodetic mass balance and provides an updated glacier hypsometry, which improves the accuracy of mass balance calculations. A modeled glacier hypsometry time-series was created to support a reanalysis of the mass balance record over the period 1960-2014, which through comparison of the geodetic and glaciological methods enables the detection of potential sources of error in the glaciological method. Comparison of the two approaches reveals that within the error margin no significant difference exists between the average annual glaciological mass balance (-213 ± 28 mm w.e. a 1) and geodetic mass balance ( 178 ± 16 mm w.e. a-1). To determine how ice dynamics have responded to ice thinning and negative mass balances, dual-frequency GPS observations of ice motion were compared to historic velocity measurements collected at three cross-sectional profiles along the glacier. Comparisons of annual and seasonal velocities indicate velocity decreases of 10–45% since the 1960s. However, increased summer velocities at the highest station suggests that increased delivery of surface meltwater to the glacier bed has initiated basal sliding at elevations that did not experience high levels of melt in earlier decades. Modeled balance fluxes demonstrate that observed fluxes, both historically and currently, are unsustainable under current climate conditions.

Styles APA, Harvard, Vancouver, ISO, etc.

15

Palmgren, Rikard. « Reconstructing the Long-Term Mass Balance of Brewster Glacier, New Zealand, Using a Degree-Day Approach ». Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-324325.

Texte intégral

Résumé :

Varmare klimat är något som kontinuerligt påverkar glaciärer planeten över och har under det senaste århundrandet vidtagit en global ökning av negativa massbalanser. Denna trend kan bidra till variationer i havsnivån och orsaka problem med översvämningar över hela världen. Övervakning och observation av världens glaciärer är därför väldigt viktigt och genom att skapa modeller som tillåter insyn i glaciärernas respons till atmosfärisk fluktuation går det att åstadkomma en djupare förståelse för hur den globala uppvärmningen kommer att utvecklas. I detta projektet återskapas massbalansen för Brewster Glacier, Nya Zeeland, för perioden 2005 – 2015 genom tillämpning av graddagar. Modellen har försetts med data från ett nyligen genomfört nedskalningsprojekt som har producerat atmosfäriska data för perioden 1979 – 2015 vilket tillåter modellen att köras. Resultaten som presenteras kommer att bidra till större inblick i graddags-modellen om huruvida tillvägagångssättet att använda enkel temperatur- och nederbördsdata är tillförlitligt för att porträttera massbalansen för glaciärer.
Warmer climate is something that is continuously affecting glaciers across the planet and has during the last century gained a global increase in negative mass balances. This trend has contributed to sea-level rise and had other impacts on water resources. Monitoring and observing the worlds glaciers is therefore very important and by creating models that allows insight in the glacier response to atmospheric fluctuation, it is possible to obtain deeper knowledge on how the global warming will develop. In this project, the mass balance of Brewster Glacier, New Zealand, is reconstructed for the period 2005 – 2015 using a degree-day approach. The input for the model has been obtained from a recent downscaling project that has produced atmospheric data over the period 1979 – 2015 that allows the model to run at a daily temporal resolution. The results presented are going to contribute to a greater insight in the degree-day model as to whether the approach of using simple air temperature and precipitation data are reliable to portray the mass balance of glaciers.

Styles APA, Harvard, Vancouver, ISO, etc.

16

McLay, Nicholas Ross. « Ice Velocity and Mass Balance Study of the Skelton Glacier, Antarctica, Using Remote Sensing and GIS Techniques ». Thesis, University of Canterbury. Gateway Antarctica, 2013. http://hdl.handle.net/10092/7883.

Texte intégral

Résumé :

The Skelton Glacier is one of the many smaller outlet glaciers located in the Transantarctic Mountains, where it drains ice into the Ross Ice Shelf. These outlet glaciers are important when determining the past, present, and future state of the mass balance of the East Antarctic Ice Sheet. This research uses satellite imagery acquired over a period of 15 years to obtain a high resolution velocity field for the Skelton Glacier which is then used to calculate the mass flux and mass balance at ten flux gates along the glacier using the input-output method. The high resolution velocity field is combined with ice thickness data and accumulation data from other sources to obtain the total mass balance. The high resolution velocity field of the Skelton Glacier was created using European Remote-Sensing Satellite 1 and 2 (ERS-1/2) Synthetic Aperture Radar (SAR) data acquired in 1996 with the processing technique of SAR interferometry (InSAR). Because of the lack of differential InSAR pairs, new auxiliary data from the ICESat and TanDEM-X mission were included into the analysis. A velocity field was created at a spatial resolution of 50m which was validated with in situ GPS measurements from 2011/12, and compared to lower resolution velocity fields of the Skelton Glacier. The ice velocity field is at improved accuracy for this area compared to previous studies and is thought to be representative for the mean ice velocity. The analysis of ice flux at several flux gates allowed an improved error estimation of the applied technique to estimate the overall mass balance. Mass flux estimates along the glacier were calculated using the new velocity field and additional thickness data, which was then compared to two accumulation datasets to give mass balance estimates along the glacier at selected flux gates. The mass flux through the grounding line was found to be 1.2165 Gt a⁻¹, which needs to be balanced in a state of mass balance equilibrium by a mean annual snow accumulation of about 185 mm a⁻¹ water equivalent over the total catchment area determined with 6569 km². The mass balance at the grounding line is slightly negative, but the second flux gate is thought to be more representative of the mass balance, which is estimated to be 0.0441 Gt a⁻¹. Error analysis of the mass balance estimates found uncertainties in this data to be approximately 0.110 Gt a⁻¹. It is concluded from the analysis that further improvements in the overall mass balance estimate can be primarily obtained by a better knowledge of ice thickness and snow accumulation.

Styles APA, Harvard, Vancouver, ISO, etc.

17

Eriksson, Rehn Ida. « Mass balance and local characteristics of three glaciers in southern Norway, between 1980 and 2018 : An analysis of the mass balance and the local characteristics of Ålfotbreen, Storbreen and Gråsubreen ». Thesis, Stockholms universitet, Institutionen för naturgeografi, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-184671.

Texte intégral

Résumé :

Glaciers are known as climate indicators because of their sensitivity towards climatic perturbations and fluctuations. A majority of the world’s glaciers are currently melting as a response to climatic perturbations. Glaciers in Norway display the same pattern, and the loss of mass have accelerated during the 1990s to this day. The glaciers of interest in this paper is situated in a west to east transect with the maritime Ålfotbreen in the west, to the continental Gråsubreen in the east, with the intermediate Storbreen in between. Differences in the local climate have a significant impact on the future state of glaciers. This paper aims to compare the mass balance, mass turnover and mass balance sensitivity of the three glaciers of interest, between the years 1980 and 2018, to demonstrate the importance of the local climate and characteristics for glacial existence. Mass balance data series of each glaciers’ mass balance was analysed. In addition, development trends of the mean annual summer air temperature for respective glaciers’ region were also conducted. A literature review of relevant reports and publications will be presented and analysed to complement the result of this paper. The results of this paper indicate that the characteristics of respective glacier vary along the increasing continentality of the west to east transect, with the mass balance sensitivity decreasing from west to east. The mass turnover displayed varying patterns, between the years 1980 and 2018. ÅLF had the highest mass turnover for the period and GRÅ the smallest with STO in between. It can be concluded, based on the result of this paper, that the fate of glaciers depends on geographical location and local characteristics. The resemblance between Storbreen and Storglaciären, and the existence of Helagsglaciären who seem to survive against the odds, strengthens the importance of local characteristics.

Styles APA, Harvard, Vancouver, ISO, etc.

18

MOSCONI, BORIS. « SOME EXAMPLES OF MODELLING GLACIER MASS BALANCE AND RESULTS FROM SNOW MELT MITIGATION STRATEGIES IN THE ITALIAN ALPS ». Doctoral thesis, Università degli Studi di Milano, 2013. http://hdl.handle.net/2434/216123.

Texte intégral

Résumé :

Abstract In this PhD Thesis were reported the main results obtained analysing melting processes at the surface of some selected Alpine glaciers. In particular mitigation strategies to reduce snow and ice ablation at the surface of the Dosdé Glacier (Lombardy Alps) and the Presena Glacier (Trentino) were analyzed to evaluate their effectiveness and applicability. Moreover some modeling approaches were applied to distribute ice and snow melting at the surface of the Dosdè debris free Glacier and the Venerocolo debris covered Glacier (Lombardy Alps) also to evaluate glacier meltwater discharge. As regards the applied strategies to reduce ice and snow melting they were performed on two different glacier sites: the Presena Glacier, where skiing activates are performed from November to June without interruptions and only a short pause occurs during the hottest summer months, and the Dosdè Glacier, an Alpine glacier without strong human impacts where only trekking and mountaineering are performed. Then on the first site the preservation of winter snow is important to guarantee the possibility of performing skiing activities also in spring and early summer and several facilities (sly lifts and snow cats among the others) area available to perform and manage the mitigation strategies. Moreover snow cover presents peculiar features (density and strength different with respect to the natural conditions) due to the action of snow cats. Differently on the Dosdè glacier snow cover derived only by snowfalls and avalanches and it presents density and strength typical of a natural and untouched cold environment. No facilities area available to perform and manage the experiments. Then on this two different glacier sites the experiments we performed had different purposes: at the Dosdè Glacier we tested on natural snow the efficiency of artificial covers to preserve snow and ice. Then only a small glacier area was covered with a special material (Iceprotector500 ©) and some instruments were installed as well to measure albedo and energy balance at the glacier surface and at the surface of the artificial cover. Differently on the Presena Glacier the Autonomous Province of Trento asked for having an assessment of the effect of a wide artificial cover (up to 70,000 m2) on the glacier mass balance as they initiated an actual program of mitigation of snow and ice ablation to change drastically the glacier mass balance and then to preserve the possibility to use the Presena Glacier as a tourist resource. On this glacier we evaluated not only the artificial cover efficiency in reducing ablation of compact snow but also we evaluated the impact of this method on the whole glacier seasonal variation. In addition on this glacier was also possible to test different artificial covers (varying their chemical compositions, their thickness and their weight per area unit) to evaluate the most convenient for such purposes. As regards the modeling of ice and snow melting we followed different approaches. The main aim was to develop a simple method capable to describe the natural variability of glacier melt starting from simple data as air temperature and solar radiation which can be easily measured or evaluated. Other main input data are glacier melt rates measured on the field at least for short period. In particular we applied an enhanced melt index obtained by considering both positive degree days and incoming solar radiation. Different attempts were performed by applying index calibration over short period (high accuracy but difficult to be applied on different years) and by calibrate the index on larger time frame (less accuracy but higher possibility of make the models running on different time windows). To calculate the whole glacier mass balance we also described temporal and spatial variability of snow coverage. This issue is particularly difficult on the Italian Alps since poor data are available to describe snow depth and density at higher elevations. Also in this case our modeling approaches started from simple and largely available data (slope, aspect and elevation of each glacier pixel) and from some fundamental field data collected at the begging and at the end of the summer periods (snow depth and density evaluated trough snow pits). To improve our snow coverage modeling we also tested the use of a georadar to acquire a large sample of snow depth data coupling such information with snow density from snow pits. Last but not least the glacier modeling approaches are based on robust series of climatic data. In fact as preliminary work we performed during the PhD was an analysis of all the available meteo data describing the climate settings of the study sites to evaluate their reliability. We check all the series (through statistical tests) thus obtaining a good record of data which constituted the main input of our glacier models and analysis. We also evaluated local lapse rates to be applied in our models. This part of the research was reported and explained in the Annex.

Styles APA, Harvard, Vancouver, ISO, etc.

19

Spiess, Marinka [Verfasser], Frank [Akademischer Betreuer] Lehmkuhl, Christoph [Akademischer Betreuer] Schneider et Dieter [Akademischer Betreuer] Scherer. « Remote sensing derived spatial patterns of glacier mass balance in Tibet / Marinka Spiess ; Frank Lehmkuhl, Christoph Schneider, Dieter Scherer ». Aachen : Universitätsbibliothek der RWTH Aachen, 2016. http://d-nb.info/1130402800/34.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

20

Young, Emma Victoria. « Determining the ability of terrestrial time-lapse microgravity surveying on a glacier to find summer mass balance using gravitational modeling ». Master's thesis, Temple University Libraries, 2017. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/473458.

Texte intégral

Résumé :

Geology
M.S.
Mass loss of alpine glaciers presently account for about half of the cryospheric contribution to the global sea-level rise. Mass balance of alpine glaciers has predominantly been monitored by; (1) glaciological and hydrological methods, and (2) satellite gravimetric methods using data from NASA’s Gravity Recovery and Climate Experiment (GRACE) satellite mission. However, the former can be logistically costly and have large extrapolation errors: measurements taken at monthly temporal scales are expensive and have a spatial resolution of roughly one kilometer. The latter provides monthly mass-balance estimates of aggregates of alpine glaciers, although the spatial resolution (~300 km) is far too coarse for assessing individual glaciers’ mass balance. Ground-based, time-lapse microgravity measurements can potentially overcome some of the disadvantages of the glaciological, hydrological, and satellite gravitational methods for assessing mass changes and their spatial distribution on a single glacier. Gravity models were utilized to predict the gravity signals of the summer-time mass balance, changes in the seasonal snow cover outside of the glacier, and the vertical gravity gradient (VGG) needed for the free-air correction on Wolverine Glacier, AK. The modeled gravity signal of the summer-time mass balance (average of -0.237 mGal) is more than an order of magnitude larger than the uncertainty of conventional relative gravimeters (±0.007 mGal). Therefore, modeling predict that the time-lapse gravitational method could detect the summer-time mass balance on Wolverine Glacier. The seasonal snow effect was shown to have the greatest influence (~ -0.15 mGal) on the outer 100 m boundary of the glacier and minimal effect (~ -0.02 mGal) towards the center, both larger than the uncertainty of relative gravimeters. The VGG has a positive deviation, about -0.1 to -0.2 mGal/m, from the normal VGG (-0.309 mGal/m). Thus, seasonal snow effect and VGG need to be correctly accounted for when processing gravity measurements to derive the residual gravity signal of the glacier mass balance. Accurate measurements of elevation changes, seasonal snow depth, and the VGG should be performed in future gravity surveys of glaciers.
Temple University--Theses

Styles APA, Harvard, Vancouver, ISO, etc.

21

Honsaker, William M. « Late-Holocene Chronology of the Istorvet Ice Cap, Liverpool Land, East Greenland ». University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1307320783.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

22

MORETTI, MASSIMILIANO. « Development and climate interpretation of mass balance and future assessment about Alpine glaciers, through theoretical models, included in Project of Interest NextData ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2016. http://hdl.handle.net/10281/104534.

Texte intégral

Résumé :

Mountains are sentinels of climate change, for their rapid response to environmental modifications (UN A/Res/62/196). The possibility of amplified warming in high-altitude regions and the associated notion of Elevation Dependent Warming, although dependent on the specific geographical area and mountain chain considered, is a topic of current interest and debate. Mountain glaciers are rapidly retreating in most of the world, especially evident on the southern side of the European Alps, where large amounts of ice mass have been lost in the last fifty years. This scenario create the condition to develop theoretical simulation model, assessing glacier response to climate change. To obtain estimates of future glacier conditions, quantitative descriptions of dynamics are adopted. The more complex models provide a detailed and realistic description of glacier dynamics, but also require a larger amount of input data. In case such information is not available, as it is often the case for most mountain glaciers, it could be safer to resort to simplified descriptions that make best use of the existing data. The term Minimal Glacier Model (MGM) indicates a class of models that do not explicitly describe the spatial dependence of the dynamical variables and develop a bulk description of the glacier in terms of glacier-averaged dynamical quantities that depend only on time. The MGMs are a simple but effective way of estimating glacier response to climate change and climate variability. In such approach, the main state variable is glacier length, depends on mean thickness and slope using a numerical experimentation with a Shallow Ice Approximation model. The evolution of the glacier length is obtained from an integrated continuity equation driven by the glacier mass balance. In this work, we adopt a description based on the MGM approach with an intensive use of Geographical Information System GIS to set parameters and geomorphological conditions. Moreover, we analysed the climate condition of Alpine region and we considered temperature and precipitation variables as climate forcing to drive the mass balance input. The aim of my Ph.D research program is to apply MGM – GIS approach with climate drivers on all glaciers of Greater Alpine Region with usable mass balance dataset. The final results are the assessments of glacier retreat until 2100, classifying average values. First of all, I used such enhanced MGM approach to investigate the dynamics of two important glaciers on the southern side of the Alps: the Careser glacier (Ortles-Cevedale group, Eastern Italian Alps), and the Rutor glacier (Aosta Valley, Western Italian Alps). After comparing the model results with the available data, I tried to estimate the future behavior of these two glaciers, using the Global Climate Models (GCM) from the CMIP5 project, considering two Representative Concentration Pathways RCP 4.5 and RCP 8.5 to include the most dramatic and the most conservative scenarios still plausible. At a later stage, I have to apply MGM on all glaciers of the GAR: I used precipitation and temperature data from E-OBS dataset, the first high-resolution gridded dataset of daily climate observations over Europe, by the European Climate Assessment & Dataset (ECA&D). Then, to drive the MGM for future climate conditions, I used the NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP) dataset: a downscaled climate scenarios for the globe that are derived from the GCM runs conducted under the CMIP5. The simulated average assessments are classified following the geographical location of glaciers, their mass balance trends, their geomorphological parameters (altitude, slope) and the different climate behaviors on the entire GAR.

Styles APA, Harvard, Vancouver, ISO, etc.

23

Wagnon, Patrick. « Analyse du bilan d'énergie d'un glacier tropical : application à la relation glacier-climat ». Phd thesis, Université Joseph Fourier (Grenoble ; 1971-2015), 1999. http://www.theses.fr/1999GRE10067.

Texte intégral

Résumé :

Les glaciers tropicaux sont des indicateurs climatiques tres sensibles. Pour relier les fluctuations de leur bilan de masse aux changements climatiques, nous avons realise un bilan d'energie a la surface du glacier zongo (16s), en bolivie, entre mars 96 et aout 98. Cette these presente, d'une part les methodes employees pour obtenir le cycle annuel du bilan d'energie ponctuel, et d'autre part l'interet de cette etude pour la comprehension du fonctionnement du glacier et sa relation avec la climatologie locale. Dans la premiere partie, nous nous attachons a decrire les conditions climatiques regnant sur ce glacier, a partir des enregistrements des stations meteorologiques installees sur le glacier zongo. Les glaciers tropicaux sont soumis a des temperatures et des radiations solaires incidentes peu variables au cours de l'annee, alors que le debit du torrent emissaire est tres saisonnier. Pour comprendre quels sont les flux d'energie responsables de la saisonnalite de la fusion en surface du glacier, nous avons dresse le bilan d'energie en un point du glacier, dans la zone d'ablation, a 5150 m d'altitude. Ce bilan d'energie traduit un metabolisme propre aux glaciers tropicaux. L'albedo est le parametre essentiel qui controle la quantite d'energie disponible pour la fusion en surface du glacier. La particularite fondamentale de ces glaciers reside en la tres forte consommation d'energie sous forme de chaleur latente (ce qui se traduit par une sublimation elevee). En outre, le flux de chaleur latente presente une saisonnalite marquee a l'origine du regime hydrologique du torrent qui s'echappe du glacier. En effet, en saison seche, la sublimation est maximale et il reste peu d'energie pour la fusion d'ou le faible debit du torrent emissaire. La situation opposee se produit en saison humide. A l'echelle de l'ensemble de la periode etudiee, le bilan de masse nettement deficitaire de l'annee el nino 1997-98 s'explique surtout par un deficit de precipitations, responsable d'une chute de l'albedo moyen annuel. Le manteau neigeux reduit lors de la saison d'accumulation 1997-98 a disparu plus vite que celui de l'annee precedente, laissant affleurer une surface de glace sale, d'albedo faible, pendant une periode plus longue. De plus, la chaleur sensible plus elevee et la sublimation reduite ont aussi contribue a augmenter la fusion superficielle, diminuant ainsi le bilan de masse du glacier.

Styles APA, Harvard, Vancouver, ISO, etc.

24

Wagnon, Patrick. « Analyse du bilan d'énergie d'un glacier tropical : application à la relation glacier-climat ». Phd thesis, Grenoble 1, 1999. http://tel.archives-ouvertes.fr/tel-00693949.

Texte intégral

Résumé :

Les glaciers tropicaux sont des indicateurs climatiques très sensibles. Pour relier les fluctuations de leur bilan de masse aux changements climatiques, nous avons réalisé un bilan d'énergie à la surface du Glacier Zongo (16°S), en Bolivie, entre mars 96 et août 98. Cette thèse présente, d'une part les méthodes employées pour obtenir le cycle annuel du bilan d'énergie ponctuel, et d'autre part l'intérêt de cette étude pour la compréhension du fonctionnement du glacier et sa relation avec la climatologie locale. Dans la première partie, nous nous attachons à décrire les conditions climatiques régnant sur ce glacier, à partir des enregistrements des stations météorologiques installées sur le Glacier Zongo. Les glaciers tropicaux sont soumis à des températures et des radiations solaires incidentes peu variables au cours de l'année, alors que le débit du torrent émissaire est très saisonnier. Pour comprendre quels sont les flux d'énergie responsables de la saisonnalité de la fusion en surface du glacier, nous avons dressé le bilan d'énergie en un point du glacier, dans la zone d'ablation, à 5150 m d'altitude. Ce bilan d'énergie traduit un métabolisme propre aux glaciers tropicaux. L'albédo est le paramètre essentiel qui contrôle la quantité d'énergie disponible pour la fusion en surface du glacier. La particularité fondamentale de ces glaciers réside en la très forte consommation d'énergie sous forme de chaleur latente (ce qui se traduit par une sublimation élevée). En outre, le flux de chaleur latente présente une saisonnalité marquée à l'origine du régime hydrologique du torrent qui s'échappe du glacier. En effet, en saison sèche, la sublimation est maximale et il reste peu d'énergie pour la fusion d'où le faible débit du torrent émissaire. La situation opposée se produit en saison humide. À l'échelle de l'ensemble de la période étudiée, le bilan de masse nettement déficitaire de l'année El Nino 1997-98 s'explique surtout par un déficit de précipitations, responsable d'une chute de l'albédo moyen annuel. Le manteau neigeux réduit lors de la saison d'accumulation 1997-98 a disparu plus vite que celui de l'année précédente, laissant affleurer une surface de glace sale, d'albédo faible, pendant une période plus longue. De plus, la chaleur sensible plus élevée et la sublimation réduite ont aussi contribué à augmenter la fusion superficielle, diminuant ainsi le bilan de masse du glacier.

Styles APA, Harvard, Vancouver, ISO, etc.

25

Macdonald, Oliver George. « Coupling glacier mass balance and meltwater yield in the European Alps with future climate change : downscaling from integrations of the HADCM model ». Thesis, University of Salford, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402055.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

26

Weidemann, Stephanie Suzanne. « Glacier response to climate variability and climate change across the Southern Andes ». Doctoral thesis, Humboldt-Universität zu Berlin, 2021. http://dx.doi.org/10.18452/22954.

Texte intégral

Résumé :

Die Gletscherschmelze in den südlichen Anden trägt maßgeblich zum Anstieg des Meeresspiegels der letzten Jahrzehnte bei und beeinflusst regional die saisonale Wasserverfügbarkeit. In jüngster Zeit wurde eine rapide Zunahme der Massenverluste insbesondere einzelner großer Auslassgletscher des Südlichen Patagonisches Eisfeldes beobachtet. Im Rahmen der Dissertation wurden die rezente Variabilität des Klimas und der klimatischen Massenbilanz für ausgewählte vergletscherte Gebiete in Patagonien und Feuerland untersucht. Die Verbesserung unseres Verständnisses über räumliche und zeitliche Muster der klimatischen Massenbilanz, ihrer atmosphärischen Antriebsfaktoren und ihres Einflusses auf das in jüngster Vergangenheit beobachtete individuelle Gletscherverhalten, sind weitere wichtige Ziele. Da die Klimavariabilität die Hauptursache für lokale Veränderungen in der Kryosphäre der südlichen Anden ist, wurden langjährige meteorologische Beobachtungen im Gebiet der Gran Campo Nevado-Eiskappe im südlichsten Patagonien im Hinblick auf räumliche und zeitliche Variabilität untersucht und der Einfluss mesoskaliger Wettermuster und Modi atmosphärischer Oszillationen auf die Ausprägung des Klimas analysiert. Darüber hinaus wurde die rezente Variabilität der klimatischen Massenbilanz für ausgewählte Gletscher in Südpatagonien und Feuerland durch die Implementierung des Energie- und Massenbilanzmodells COSIMA simuliert. Eine unterschiedliche Ausprägung der Oberflächenmassenbilanz und geodätischer Massenbilanz unterstreicht wie wichtig ein besseres Verständnis über die Prozesse der klimatischen Massenbilanz und Eisdynamik ist. Des Weiteren wurden Simulationen der klimatischen Massenbilanz eingesetzt, um eine ausgeglichene Massenbilanz für rezente und vergangene Ausdehnungen des Gletschers Schiaparelli abzuleiten. Ziel war es, eine modellgestützte Annäherung an die klimatischen Bedingungen während der Kleinen Eiszeit zu simulieren.
Glacier mass loss of the Southern Andes contributes largely to sea-level rise during recent decades and also affects the regional water availability. Despite the overall glacier retreat of most glaciers in Patagonia and Tierra del Fuego, a recent increase in mass loss of individual glaciers has been observed. The recent variability of climate and climatic mass balance for selected glaciated study sites in Patagonia and Tierra del Fuego are investigated in this thesis. Improving our understanding on the spatial and temporal variations of climatic mass balance processes, its atmospheric drivers, and their impact on the recently observed individual glacier behavior are further important aims. Since climate variability is the key driver of local changes in the cryosphere in the Southern Andes, a unique record of meteorological observations across the Gran Campo Nevado Ice Cap in Southernmost Patagonia was analyzed with regard to main climate features and the relationship between the in-situ observations, large-scale climate modes and mesoscale weather patterns. Furthermore, recent climatic mass balance variability was simulated for selected glaciers in Southern Patagonia and Tierra del Fuego by implementing the ’COupled Snow and Ice energy and MAss balance model’ COSIMA. Contrasting patterns of positive simulated annual climatic mass balance and clearly negative geodetic mass balance were found for two neighboring glaciers of the Southern Patagonia Icefield between 2000 and 2014. This highlights the importance of understanding of both, the climatic mass balance, and the ice-dynamical processes. Climatic mass balance simulations were further used to derive glacier steady-state conditions for recent and past glacier extents of Schiaparelli Glacier, aiming for a model-based approximation of climate conditions during the Little Ice Age.

Styles APA, Harvard, Vancouver, ISO, etc.

27

Klingbjer, Per. « Glaciers and climate in northern Sweden during the 19th and 20th century ». Doctoral thesis, Stockholm : Institutionen för naturgeografi och kvartärgeologi, Stockholms universitet, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-92.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

28

Mohd, Farooq Azam. « Relation climat-glacier dans la zone de transition entre climat aride et mousson indienne : un cas d'étude dans l'Himachal Pradesh Inde ». Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU032/document.

Texte intégral

Résumé :

La région de l'Hindu-Kush Karakoram Himalaya (HKH) est la plus grande région englacée de la planète, hormis les calottes polaires. Dans cette région, les mesures météorologiques et de bilans de masse sont sporadiques et les observations glaciologiques concernent essentiellement les mesures de fluctuations des fronts des glaciers. Ainsi, la réponse de ces glaciers aux changements climatiques est très mal connue. Le but de ce travail de thèse est d'améliorer la connaissance des relations entre les variables météorologiques et les bilans de masse glaciaires à partir de l'étude du glacier du Chhota Shigri situé dans l'Ouest de l'Himalaya. De nombreuses mesures in-situ de bilans de masse, de vitesses d'écoulement, d'épaisseurs et de météorologie ont été réalisées depuis 2002 et au cours de ce PhD. Ces observations permettent d'analyser le comportement du glacier au regard des fluctuations climatiques. Entre 2002 et 2013, nos observations indiquent une perte de masse cumulée équivalente à une lame d'eau de -6.45 m. Par ailleurs, l'analyse des observations des flux de glace suggèrent que le glacier a connu un état proche d'un état d'équilibre avec des bilans nuls ou légèrement positifs au cours des années 1990. Nous avons dans un premier temps reconstitué les bilans de masse annuels et saisonniers depuis 1969 en utilisant un modèle degré-jour et des variables météorologiques simples, précipitations et températures. Depuis 1969, les bilans de masse sont faiblement négatifs, équivalents à -0.30 m d'eau par an. Cette reconstitution montre que le glacier était proche de l'état d'équilibre entre 1986 et 2000, ce qui confirme les résultats obtenus à partir de l'analyse des flux de glace et des mesures géodésiques. Cette étude montre également que la perte de masse glaciaire est récente et révèle des fluctuations de bilans de masse avant l'année 2000 très différentes de ce que l'on trouve dans la littérature. L'analyse des bilans de masse à l'échelle décennale révèle que les précipitations hivernales et les températures estivales jouent un rôle sensiblement équivalent. Afin de comprendre plus en détail les variables climatiques qui contrôlent le bilan de masse, nous avons, dans un second temps, analysé les flux d'énergie en surface à l'aide de stations météorologiques situées sur le glacier et à proximité du glacier. Le rayonnement de courtes longueurs d'onde contrôlent 80 % des flux d'énergie entrant en surface alors que les flux de chaleur latente, sensible et de conduction contribuent pour 13, 5 et 2 % respectivement du flux entrant total. Par ailleurs, notre étude montre que les événements de fortes précipitations au cours de la période de mousson jouent un rôle essentiel sur l'évolution des bilans de masse. Néanmoins, à cause du manque de données de précipitation dans cette région et le fort gradient régional, la distribution des précipitations sur le glacier reste mal connue
The Hindu-Kush Karakoram Himalayan (HKH) region is the largest snow and ice reservoir on the planet outside the Polar Regions. In the HKH region the mass balance and meteorological observations are sparse and the historical knowledge is mainly concentrated on snout fluctuation records. Hitherto, the understanding of glacier-climate relationship is poor in the HKH region. Therefore, the goal of the present work is to improve the understanding of glacier-climate relationship on a representative glacier ‘Chhota Shigri' in the western Himalaya. A number of in-situ measurements concerning mass balances, surface velocity, ice thickness and meteorology have been collected during and before the present PhD work since 2002. These data sets were first analyzed to understand the glacier behaviour and then used in the models to understand the glacier relationship with climatic variables. Between 2002 and 2013, glacier showed a mass wastage/unsteady-state conditions with a cumulative mass loss of –6.45 m w.e. Further, the ice flux analysis over 2002-2010 suggested that the glacier has experienced a period of steady-state or slightly positive mass balance during the 1990s. We first reconstructed the annual and seasonal mass balances using a degree day model from simple meteorological variables, precipitation and temperature. This reconstruction allowed us to examine the mass balances between 1969 and 2012. Since 1969, Chhota Shigri showed a moderate mean mass wastage at a rate of −0.30 m w.e. a-1. A period of steady-state between 1986 and 2000, already suggested by ice flux analysis and geodetic measurements, was confirmed. The mass balance evolution of this glacier revealed that the mass wastage is recent and provide a very different pattern than that of usually found in the literature on western Himalayan glaciers. The analysis of decadal time scale mass balances with meteorological variables suggested that winter precipitation and summer temperature are almost equally important drivers controlling the mass balance pattern of this glacier. Second, in order to understand the detailed physical basis of climatic drivers, a surface energy balance study was also performed using the in-situ meteorological data from the ablation area of Chhota Shigri Glacier. Net all-wave radiation was the main heat flux towards surface with 80% contribution while sensible, latent heat and conductive heat fluxes shared 13%, 5% and 2% of total heat flux, respectively. Our study showed that the intensity of snowfall events during the summer-monsoon is among the most important drivers responsible for glacier-wide mass balance evolution of Chhota Shigri Glacier. However, due to the lack of precipitation measurements and the strong precipitation gradient in this region, the distribution of precipitation on the glacier remains unknown and needs further detailed investigations

Styles APA, Harvard, Vancouver, ISO, etc.

29

McCoy, Kurt J. « Estimation of vertical infiltration into deep Pittsburgh coal mines of WV-PA a fluid mass balance approach / ». Morgantown, W. Va. : [West Virginia University Libraries], 2002. https://etd.wvu.edu/etd/controller.jsp?moduleName=documentdata&jsp%5FetdId=2745.

Texte intégral

Résumé :

Thesis (M.S.)--West Virginia University, 2002.
Title from document title page. Document formatted into pages; contains x, 150 p. : ill. (some col.), maps (some col.). Includes abstract. Includes bibliographical references (p. 87-90).

Styles APA, Harvard, Vancouver, ISO, etc.

30

Runeskog, Henrik. « Continuous Balance Evaluation by Image Analysis of Live Video : Fall Prevention Through Pose Estimation ». Thesis, KTH, Skolan för kemi, bioteknologi och hälsa (CBH), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-297541.

Texte intégral

Résumé :

The deep learning technique Human Pose Estimation (or Human Keypoint Detection) is a promising field in tracking a person and identifying its posture. As posture and balance are two closely related concepts, the use of human pose estimation could be applied to fall prevention. By deriving the location of a persons Center of Mass and thereafter its Center of Pressure, one can evaluate the balance of a person without the use of force plates or sensors and solely using cameras. In this study, a human pose estimation model together with a predefined human weight distribution model were used to extract the location of a persons Center of Pressure in real time. The proposed method utilized two different methods of acquiring depth information from the frames - stereoscopy through two RGB-cameras and with the use of one RGB-depth camera. The estimated location of the Center of Pressure were compared to the location of the same parameter extracted while using the force plate Wii Balance Board. As the proposed method were to operate in real-time and without the use of computational processor enhancement, the choice of human pose estimation model were aimed to maximize software input/output speed. Thus, three models were used - one smaller and faster model called Lightweight Pose Network, one larger and accurate model called High-Resolution Network and one model placing itself somewhere in between the two other models, namely Pose Residual Network. The proposed method showed promising results for a real-time method of acquiring balance parameters. Although the largest source of error were the acquisition of depth information from the cameras. The results also showed that using a smaller and faster human pose estimation model proved to be sufficient in relation to the larger more accurate models in real-time usage and without the use of computational processor enhancement.
Djupinlärningstekniken Kroppshållningsestimation är ett lovande medel gällande att följa en person och identifiera dess kroppshållning. Eftersom kroppshållning och balans är två närliggande koncept, kan användning av kroppshållningsestimation appliceras till fallprevention. Genom att härleda läget för en persons tyngdpunkt och därefter läget för dess tryckcentrum, kan utvärdering en persons balans genomföras utan att använda kraftplattor eller sensorer och att enbart använda kameror. I denna studie har en kroppshållningsestimationmodell tillsammans med en fördefinierad kroppsviktfördelning använts för att extrahera läget för en persons tryckcentrum i realtid. Den föreslagna metoden använder två olika metoder för att utvinna djupseende av bilderna från kameror - stereoskopi genom användning av två RGB-kameror eller genom användning av en RGB-djupseende kamera. Det estimerade läget av tryckcentrat jämfördes med läget av samma parameter utvunnet genom användning av tryckplattan Wii Balance Board. Eftersom den föreslagna metoden var ämnad att fungera i realtid och utan hjälp av en GPU, blev valet av kroppshållningsestimationsmodellen inriktat på att maximera mjukvaruhastighet. Därför användes tre olika modeller - en mindre och snabbare modell vid namn Lightweight Pose Network, en större och mer träffsäker modell vid namn High-Resolution Network och en model som placerar sig någonstans mitt emellan de två andra modellerna gällande snabbhet och träffsäkerhet vid namn Pose Resolution Network. Den föreslagna metoden visade lovande resultat för utvinning av balansparametrar i realtid, fastän den största felfaktorn visade sig vara djupseendetekniken. Resultaten visade att användning av en mindre och snabbare kroppshållningsestimationsmodellen påvisar att hålla måttet i jämförelse med större och mer träffsäkra modeller vid användning i realtid och utan användning av externa dataprocessorer.

Styles APA, Harvard, Vancouver, ISO, etc.

31

FUGAZZA, DAVIDE. « ALL EYES ON GLACIERS : REMOTE SENSING OF THE CRYOSPHERE ». Doctoral thesis, Università degli Studi di Milano, 2019. http://hdl.handle.net/2434/623598.

Texte intégral

Résumé :

Remote sensing has become an invaluable tool for glaciologists. The keys to its success are the ability to repeatedly monitor small to large, often inaccessible areas and quickly process data through the integration in geographical information system (GIS) environments. From aerial photography in the early days, remote sensing has evolved owing to the ever-increasing input of large amounts of data from satellite platforms, while traditional photogrammetric techniques are now experiencing a renaissance thanks to the growing importance of UAVs and terrestrial photography. This Ph.D. thesis explores remote sensing applications for cryospheric monitoring and is aimed at improving our understanding of processes of glacier retreat, energy budget, mass balance and dynamics and of snow cover variability, using a variety of sensors (optical and thermal cameras, laser scanners) and platforms, including satellites, planes and unmanned aerial vehicles (UAVs). Each chapter of the thesis presents a case study: • The creation of an inventory of glaciers and potentially dangerous glacial lakes of the Central Karakorum National Park, Pakistan (Chapter 3) using Landsat satellite data. Both glaciers and lakes are very important to monitor as they are both a source of water and a potential hazard in the area. • The analysis of thickness changes and hazards related to the downwasting and collapse of Forni Glacier, a large glacier in the Italian Alps, through a combination of approaches, i.e. Laser scanner, UAV and terrestrial photogrammetry (Chapter 4). • The spatial distribution of glacier albedo (Chapter 5), important to estimate ice and snow melt for a large valley glacier in the Italian Alps (Forni Glacier) validating a pre-existing methodology using Landsat satellite data • The evolution of glacier albedo through time (chapter 6) for a selection of glaciers in the Italian Alps, Ortles-Cevedale group, extending the approach described in chapter 5, to understand the extent of glacier darkening and the potential causes. • The evolution of supraglacial debris cover for a selection of glaciers in the Italian Alps, Ortles-Cevedale group (chapter 7) using aerial orthoimagery. This analysis is fundamental to model the melt of debris covered glaciers and understand their evolution. • The structural evolution of the glacier tongue of a large valley glacier (Forni Glacier) using aerial and UAV imagery, to investigate the changes in glacier dynamics over time (Chapter 8). • The analysis of multiannual variability of snow cover in a large river basin of Central Asia (Upper Irtysh, Kazakhstan) and the relationship between snow cover depletion and atmospheric circulation indices using MODIS satellite data (Chapter 9), to provide useful tools for flood forecasting. The key findings from Chapters 4 to 8 permit to assess the evolution of a wide glacier area of the Italian Alps, highlighting the increase in supraglacial debris cover and related decrease in glacier albedo, increased rates of glacier downwasting and structural collapse, increasing the potential for glacier hazards. The analysis of glacier hazards was also an important part of the CKNP study, including an assessment of the current state of glaciers and glacial lakes. The focus on snow cover variability in Central Asia shows instead the importance of atmospheric circulation and the possibility of long-term forecasts using widely available teleconnection indices. Most relevant processes in the cryosphere were touched upon in this thesis, from accumulation processes (i.e. snow cover), to melt (including albedo and debris cover which influence it) and structural characteristics. Furthermore, while the case studies can be read as independent units, all the methodologies presented here transcend the single example and are widely applicable to different glaciers or areas. In particular, glacier albedo or debris cover maps are an essential input to improve glacier melt models, and could be used in the CKNP to model melt more accurately. Glacier mass balance and dynamics could also be monitored more accurately and at unprecedented spatial resolution using UAVs.

Styles APA, Harvard, Vancouver, ISO, etc.

32

Dumont, Marie. « Détermination de l'albédo des surfaces enneigées par télédétection : application à la reconstruction du bilan de masse du glacier de Saint Sorlin ». Phd thesis, Université Paris-Est, 2010. http://tel.archives-ouvertes.fr/tel-00582925.

Texte intégral

Résumé :

L'albédo, fraction de rayonnement réfléchi dans le spectre solaire, est une variable clef du bilan énergétique des surfaces enneigées et englacées. Cette grandeur possède une forte variabilité spatio-temporelle ce qui fait de la télédétection un outil adapté pour son étude. L'albédo dépend à la fois des propriétés physiques du milieu considéré et des caractéristiques du rayonnement incident. Les différentes grandeurs liées à l'albédo sont fonction des domaines angulaires et spectraux des radiations considérées. Les mesures de répartition angulaire du rayonnement réfléchi par la neige ont montré que l'hypothèse lambertienne pouvait conduire à des erreurs non négligeables lors de la détermination de l'albédo par télédétection. La connaissance des caractéristiques de la répartition angulaire du rayonnement réfléchi par la neige permet de développer une nouvelle méthode de détermination de l'albédo en zones montagneuses. Cette méthode prend en compte les effets liés à la forte variabilité topographique des terrains de montagne, à l'anisotropie du rayonnement réfléchi par la neige et par la glace ainsi que les variations spectrales de l'albédo en fonction des propriétés physiques de la surface. Elle a été appliquée à deux types de données : des photographies terrestres visibles et proche infrarouges (résolution spatiale 10 m) et des images MODIS (résolution spatiale 250 m). L'incertitude sur la valeur de l'albédo ainsi déterminée est évaluée à ±10% grâce aux mesures de terrain effectuées sur le glacier de Saint Sorlin (massif des Grandes Rousses, France). L'étude des cartes d'albédo issues de dix années (2000-2009) d'images MODIS montre qu'il n'y a pas de décroissance marquée de la valeur de l'albédo en zone d'ablation au contraire de ce qui a été prouvé pour le glacier du Morteratsch (Suisse). De plus, il existe une corrélation très élevée entre la valeur minimale de la moyenne de l'albédo sur le glacier, i.e. l'albédo moyen du glacier le jour où la ligne de neige est proche de la ligne d'équilibre, et la valeur du bilan de masse annuel spéciﬁque. L'assimilation des données d'albédo obtenues grâce aux images MODIS et aux photographies terrestres dans le modèle de neige CROCUS permet une bonne estimation du bilan de masse spatialisé du glacier de Saint Sorlin (rmse=0.5 m w.e. pour les cinq années hydrologiques étudiées). Les forçages météorologiques utilisés pour cette étude sont de moyenne échelle. L'analyse succincte de la contribution des différents ﬂux atmosphériques au bilan d'énergie de surface montre qu'en zone d'ablation comme en zone d'accumulation, le bilan radiatif net courtes longueurs d'ondes constitue la source principale d'énergie et que la variabilité de ce ﬂux explique la majeure partie de la variabilité journalière de la somme des ﬂux atmosphériques. Appliquées à d'autres glaciers, ces méthodes permettraient de savoir si les conclusions établies pour notre seul glacier d'étude sont valables pour d'autres glaciers. Elles rendraient également possibles la reconstruction du bilan de masse spatialisé sur 10 ans d'autres glaciers et potentiellement une meilleure quantification des processus physiques mis en jeu dans le bilan de masse de ces glaciers tempérés

Styles APA, Harvard, Vancouver, ISO, etc.

33

Riger-Kusk, Mette. « Ice dynamics of the Darwin-Hatherton glacial system, Transantarctic Mountains, Antarctica ». Thesis, University of Canterbury. Geography, 2011. http://hdl.handle.net/10092/6602.

Texte intégral

Résumé :

The Darwin-Hatherton glacial system (DHGS) drains from the East Antarctic Ice Sheet (EAIS) and through the Transantarctic Mountains (TAM) before entering the Ross Embayment. Large ice-free areas covered in glacial sediments surround the DHGS, and at least five glacial drift sheets mark the limits of previous ice extent. The glacier belongs to a group of slow-moving EAIS outlet glaciers which are poorly understood. Despite this, an extrapolation of a glacial drift sheet boundary has been used to determine the thickness of the EAIS and the advanced West Antarctic Ice Sheet (WAIS) during the Last Glacial Maximum (LGM). In order to accurately determine the past and present contributions of the Antarctic ice sheets to sea level changes, these uncertainties should be reduced. This study aims to examine the present and LGM ice dynamics of the DHGS by combining newly acquired field measurements with a 3-D numerical ice sheet-shelf model. The fieldwork included a ground penetrating radar survey of ice thickness and surface velocity measurements by GPS. In addition, an extensive dataset of airborne radar measurements and meteorological recordings from automatic weather stations were made available. The model setup involved nesting a high-resolution (1 km) model of the DHGS within a lower resolution (20 km) all-Antarctic simulation. The nested 3-D modelling procedure enables an examination of the impact of changes of the EAIS and WAIS on the DHGS behaviour, and accounts for a complex glacier morphology and surface mass balance within the glacial system. The findings of this study illustrate the difference in ice dynamics between the Darwin and Hatherton Glaciers. The Darwin Glacier is up to 1500 m thick, partially warm-based, has high driving stresses (~150 kPa), and measured ice velocities increase from 20-30 m yr⁻¹ in the upper parts to ~180 m yr⁻¹ in the lowermost steepest regions, where modelled flow velocities peak at 330 m yr⁻¹. In comparison, the Hatherton Glacier is relatively thin (<900 m), completely cold-based, has low driving stresses (~85 kPa), and is likely to flow with velocities <10 m yr⁻¹ in most regions. It is inferred that the slow velocities with which the DHGS flows are a result of high subglacial mountains restricting ice flow from the EAIS, large regions of frozen basal conditions, low SMB and undulating bedrock topography. The model simulation of LGM ice conditions within the DHGS implies that the ice thickness of the WAIS has been significantly overestimated in previous reconstructions. Results show that the surface of the WAIS and EAIS away from the TAM would have been elevated 600-750 and 0-80 m above present-day levels, respectively, for the DHGS to reach what was inferred to represent the LGM drift sheet limit. Ultimately, this research contributes towards a better understanding of the dynamic behaviour of slow moving TAM outlet glaciers, and provides new insight into past changes of the EAIS and WAIS. This will facilitate more accurate quantifications of contributions of the WAIS and EAIS to changes in global sea level.

Styles APA, Harvard, Vancouver, ISO, etc.

34

Hedfors, Jim. « Force Budget Analysis of Glacier Flow : Ice Dynamical Studies on Storglaciären, Sweden, and Ice Flow Investigations of Outlet Glaciers in Dronning Maud Land, Antarctica ». Doctoral thesis, Uppsala University, Department of Earth Sciences, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4219.

Texte intégral

Résumé :

This thesis contributes to the understanding of glacier response to climate change by ice dynamical studies on Storglaciären, Sweden, and Bonnevie-Svendsenbreen, Kibergbreen and Plogbreen in Dronning Maud Land, Antarctica. Ice surface velocities, ice geometry and temperature information is fed through a force budget model to calculate ice mass outflux of these glacial systems via three-dimensional stress distributions for a flux-gate.

Field data were collected through repeated DGPS and GPR observations on Storglaciären between July 2000 to September 2001 and on Kibergbreen and Plobreen during the SWEDARP 2002/03 expedition to Antarctica. The work was strongly supported by remotely-sensed information.

The results from Storglaciären show a strength in the force budget model to discern both spatial and temporal variability in ice dynamical patterns. It highlights the influence of seasonality and bedrock topography upon glacier flow. A modeling experiment on Bonnevie-Svendsenbreen suggested that ice temperature increases substantially under conditions of high stress (≥0.4 MPa) due to strain-heating. This provides a positive feedback loop, increasing ice deformation, as long as it overcomes the advection of cool ice from the surface. These results explain, to some extent, the mechanism behind fast flowing ice streams. Mass flux caclulations from Bonnevie-Svendsenbreen suggest that the outflux given from force budget calculations can be used as a gauge for influx assuming steady state conditions. Plogbreen receives an influx of 0.48±0.1 km³ a^-1 and expedites a discharge volume of 0.55±0.05 km³ a^-1. This indicative negative mass balance is explained by a falling trend in upstream accumulation and the recent rise in global sea level, as it is likely to induce glacier acceleration due to a reduction in resistive forces at the site of the gate. This result is comparable with other Antarctic studies reporting negative mass balances, e.g. from WAIS, as caused by changes in the global atmospheric circulation pattern.

Styles APA, Harvard, Vancouver, ISO, etc.

35

Muñoz-Cobo, Belart Joaquín. « Bilan de masse des glaciers islandais depuis 1945 : reconstruction et relation avec la variabilité climatique ». Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30236.

Texte intégral

Résumé :

Le bilan de masse des glaciers est fortement lié au climat. Aux hautes latitudes, l'accumulation de neige pendant l'hiver et la fonte de glace pendant l'été sont les principales composantes du bilan de masse. En Islande, le bilan de masse des trois plus larges calottes glaciaires (~600-~8000 km²) a été suivi régulièrement depuis 25 ans notamment grâce à des mesures in situ. Mais les bilans de masse des autres glaciers et calottes glaciaires islandaises ont été très peu étudiés. Aujourd'hui, les données de télédétection, notamment via la comparaison des modèles numériques du terrain (MNT), permettent de mesurer le bilan de masse par la méthode géodésique. Pour ces glaciers et calottes de plus petites tailles (de 1 km² et à quelques centaines de km²), les photographies aériennes, l'imagerie satellitaire stéréoscopique sub-métriques, et le lidar aérien sont parfaitement adaptées. Cette thèse se focalise donc sur l'estimation des bilans de masse des " petits " glaciers et calottes islandaises depuis le pas de temps saisonnier jusqu'à pluri-décennal et leur relation avec les variations spatiales et temporelles du climat. Le bilan de masse hivernal de la calotte du Drangajökull (NO-Islande) a été mesuré par des images satellitaires stéréoscopiques sub-métriques (données Pléiades et WorldView-2) acquises au début, milieu et à la fin de l'hiver 2014-2015. Les changements de volume ont été convertis en bilan de masse grâce à des mesures in situ de densité de neige, et validés avec des mesures in situ de profondeur de neige. Ce travail permet d'envisager désormais un suivi du bilan de masse saisonnier sans un laborieux travail de terrain. Une importante archive de photographies aériennes est disponible en Islande depuis 1945. Ces données offrent une revisite de 5 à 20 ans pour la majorité des glaciers. De plus, depuis 2000, cette archive est complétée par les données des capteurs satellitaires stéréoscopiques et de lidar aérien acquis entre 2008 et 2013. Cet ensemble de données est exploité pour créer une série temporelle de 70 ans de bilan de masse en Islande. La calotte d'Eyjafjallajökull (~70 km²) sert de zone test pour la création et l'automatisation d'une chaîne de traitement, basée sur des logiciels libres. [....]
The mass balance of a glacier is strongly connected to climate. At high latitudes, mass balance is typically controlled by snow accumulation during the winter and the glacier ablation during the summer. In Iceland, direct mass balance observations have been mostly focused on the three largest ice caps (~600 to ~8000 km2), measured in situ for the last 25 years. There are, however, glaciers and ice caps distributed over all quarters of the country that lack mass balance observations. Remote sensing data with the capability to retrieve the glacier surface geometry through Digital Elevation Models (DEMs) are valuable tools to measure mass balance using the geodetic method. For a typical Icelandic glacier (with an area between 1 km2 and hundreds of km2), this can be optimally achieved from optical stereoscopic imagery, emplaced in airborne or spaceborne sensors, and from airborne lidar. This thesis focuses on remote sensing techniques to accurately measure geodetic mass balance from seasonal to decadal time spans and the relationship of mass balance to climate. As an example of seasonal mass balance, the winter mass balance of Drangajökull was measured from satellite sub-meter stereo images at the beginning, middle and end of the 2014-2015 winter using data from the Pléiades and WorldView-2 satellites. The results were complemented with in situ snow density measurements and validated with snow thickness measurements. The study concludes that images from the sensors mentioned above may often be used to monitor seasonal mass balance without tedious field logistics. A vast archive of aerial photographs exists for Iceland extending back to 1945. Since then, most glaciers were surveyed every 5 to 20 years. In addition, a wealth of modern satellite stereo images is available since the early 2000s as well as airborne lidar data in 2008-2013. This creates a unique dataset to construct a 70-year time series of geodetic mass balances.[...]

Styles APA, Harvard, Vancouver, ISO, etc.

36

Davaze, Lucas. « Quantification du bilan de masse des glaciers de montagne à l'échelle régionale par télédétection spatiale optique ». Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAU022/document.

Texte intégral

Résumé :

Au-delà de leur rôle d’icône du changement climatique, les glaciers de montagne sont une composante essentielle de notre planète. Ils sont, de plus, de véritables « climat-mètres » naturels. Malgré leur faible superficie (0.5% des terres émergées), les glaciers de montagne contribuent à hauteur de 30% à la hausse du niveau des mers. Dans certaines régions, ils constituent de véritables enjeux quant à l’eau potable, l’agriculture, la production hydroélectrique ou les aléas glaciaires. Peu sont en revanche instrumentés (<0.0025%) et leurs fluctuations à l’échelle de régions entières sont mal connues.Grâce au développement de capteurs satellitaires à haute résolution spatiale (métrique à décamétrique), le développement de méthodes automatisées permet aujourd’hui d’augmenter considérablement le nombre de glaciers observés. Après avoir dressé un état de l’art des méthodes existantes et identifié les verrous méthodologiques, nous avons développé deux méthodes en particulier.La première se base sur la détection automatique de l’altitude de la limite glace/neige (i.e. ligne de neige) à la surface du glacier, à partir d’images satellites optiques. Cette altitude, lorsque mesurée à la fin de l’été, est un marqueur du changement de masse à la surface du glacier ayant eu lieu au cours de l’année (appelé bilan de masse de surface). Cette approche nous a permis d’estimer le bilan de masse de surface annuel de 239 glaciers dans les Alpes européennes et de 82 glaciers dans les Andes tropicales pour la période 2000-2016 et 2000-2018, respectivement. La perte moyenne annuelle observée est de -0.74 et de -1.29 m équivalent eau par an pour les deux régions respectivement. A notre connaissance, cette approche a permis d’établir le premier jeu de données de bilans de masse de surface annuels pour des glaciers individuels à échelle régionale à partir d’images satellites optiques. Une dépendance du bilan de masse de surface moyen par glacier à des caractères morpho-topographiques (e.g. pente, altitude médiane …) a été observée, où plus les glaciers sont pentus et hauts en altitude, moins leur perte de masse est importante. Une comparaison avec des mesures in situ dans les Alpes Européennes révèle une surestimation de la perte de masse par ces dernières si on les extrapole spatialement, notamment à cause de la faible représentation de glaciers à forte pente (>20°) dans les mesures in situ. Notre étude sur les Alpes Européennes a de plus permis d’identifier une variabilité interannuelle hétérogène sur cette région, en partie expliquée par des contextes climatiques différents grâce à l’utilisation de données issues de ré-analyses.Le développement d’une autre méthode a permis, à partir de l’analyse de carte d’albédo issues du capteur MODIS, de caractériser le bilan de masse de surface annuel et estival de 30 glaciers dans les Alpes françaises. Cette étude ouvre la porte à l’utilisation de cette méthode pour l’analyse du bilan annuel et saisonnier à l’échelle régionale.Ce travail a permis, à travers des applications dans différentes régions englacées, de développer et valider des méthodes capables, à partir d’images satellites optiques, d’estimer le bilan de masse de surface annuel et saisonnier de glaciers de montagne à l’échelle de régions entières. Ces estimations peuvent ensuite être utilisées pour : (1) étudier l’impact du climat local sur les glaciers de montagne ; (2) d’investiguer de possibles conditions météorologiques favorisant les fluctuations observées ; (3) calibrer et valider les modèles glacio-hydrologiques utilisés pour estimer les contributions actuelles et futures des glaciers de montagne au fonctionnement hydrologique des bassins versants et à l'élévation du niveau des mers
Beyond their iconic role of climate change, mountain glaciers can be considered as Earth’ essential component and natural “climate-meter”. Despite their small spatial coverage (0.5% of emerged land), mountain glaciers contribute as high as 30% of the observed sea-level rise. In some regions, they are considered as essential issues because of their importance in terms of potable water, agriculture, hydroelectricity or natural hazards. A small share is however monitored in situ (<0.0025%) and their fluctuations at regional scale are poorly known.Thanks to the development of high spatial resolution satellite sensors (metric to decametric), new methods are today available to significantly increase the number of monitored glaciers. After a state of the art of the existing methods and an identification of the limitations, we focused our attention on the development of two methods.The first one is based on the automatic detection of the snow/ice interface altitude (i.e. snowline) at the glacier surface from optical satellite images. This altitude, when estimated at the end of summer, is a proxy of the annual glacier-wide mass change at the glacier surface (called surface mass balance, SMB). Using this approach, we estimated the annual SMBs of 239 glaciers in the European Alps and 82 glaciers in the tropical Andes for the period 2000-2016 and 2000-2018, respectively. The mean mass loss are -0.74 and -1.29 m water equivalent per year for the two regions, respectively. This approach allowed to derive the first dataset of annual SMBs for individual glaciers at regional scale from optical remote sensing. We found significant relationships between the computed SMBs and the glacier morpho-topographic features (e.g. slope, median altitude, …), with steeper and higher glaciers, experiencing less mass losses. Comparison with in situ monitored SMBs revealed an overestimation of mass losses from in situ estimates, due to a low representativeness of steep glaciers (>20°) in the in situ datasets. Our study also revealed heterogeneous inter-annual variability across the European Alps, partially explained by the climatic context of the studied sub-regions, thanks to the analysis of climate reanalysis data.We developed a second method to derive the annual and summer SMBs from albedo maps, computed from MODIS images. With an application on 30 glaciers in the French Alps, this work opened the way toward a regional application of this method, in order to estimate both annual and summer SMBs.By performing regional applications on different glacierized regions, we developed and validated methods capable of deriving the annual and summer SMBs of individual mountain glaciers at regional scale, from optical remote sensing data. These data could then be used to (1) assess the impact of peculiar climatic conditions onto mountain glaciers; (2) investigate possible meteorological conditions driving the documented glacier fluctuations; (3) calibrate and validate glacio-hydrological models used to estimate the current and future contributions of mountain glaciers to the hydrological functioning of mountain catchments and to sea level rise

Styles APA, Harvard, Vancouver, ISO, etc.

37

Dussaillant, Inés. « Contribution récente des glaciers des Andes à la ressource en eau et à la hausse du niveau marin : apport des observations satellitaires ». Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30161.

Texte intégral

Résumé :

Les glaciers Andins présentent des taux de recul parmi les plus importants au monde, et contribuent à la hausse du niveau des mers. Ils constituent aussi des ressources en eau vitales pour les vastes zones semi-arides le long de la Cordillère des Andes (10°N-56°S), en alimentant les rivières lors des sécheresses. En dépit du retrait des glaciers Andins, les mesures directes des fluctuations glaciaires sont éparses, de court terme, incomplètes, et ne permettent donc pas une estimation précise de la perte de glace récente à l'échelle de la chaîne entière. Décrire quantitativement cette perte à différentes échelles spatio-temporelle est cruciale afin de mieux anticiper les impacts écologiques, économiques et sociaux. Premièrement, nous avons évalué la performance d'une méthode visant à calculer les changements de masse des glaciers Andins. Cette méthode utilise les séries temporelles des modèles numériques de terrain (DEM) produit par des images stéréoscopiques Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Sur la zone de validation de la méthode, le Champ de Glace Nord de Patagonie (NPI), nous avons observé un bilan de masse fortement négatif de -1.06 ± 0.14 m w.e. a-1 pour la période 2000-2012. Ces résultats sont cohérent avec les estimations faites précédemment, mais aussi avec une seconde estimation (-1.02 ± 0.21 m w.e. a-1) obtenue indépendamment par différentiation de DEMs de meilleur résolution, Shuttle Radar Topography Mission (SRTM) et Satellite pour l'Observation de la Terre 5 (SPOT5). Ce travail nous a permis de (i) valider la méthode appelée " ASTER monitoring Ice towards eXtinction " (ASTERIX) sur la totalité des Andes, (ii) confirmer l'absence de pénétration du signal radar SRTM dans la bande C sur la neige du NPI (sauf pour une petite région au dessus de 2900 m a.s.l) avec des effets négligeables sur le bilan de masse du NPI; et enfin (iii) fournir la base de travail pour une analyse des variations du bilan de masse du NPI durant différentes sous périodes entre 1975 et 2016, grâce à des DEMs supplémentaires. Ensuite, nous avons généré plus de 30000 DEMs ASTER afin de calculer la perte de l'intégralité des glaciers Andins, et ce pour les deux dernières décennies. La perte de masse à l'échelle des Andes s'élève ainsi à -22.9 ± 5.9 Gt a-1 (-0.72 ± 0.22 m w.e. a-1) pour la période d'étude entière, ou -26.0 ± 6.0 Gt a-1 en incluant les pertes subaquatiques. Toutes les régions affichent une diminution du volume de glace. Les taux les plus négatifs sont observés dans les Andes Patagoniennes (-0.78 ± 0.25 m w.e. a-1) et dans les Andes Tropicales (-0.42 ± 0.24 m w.e. a-1). Les pertes sont modérées dans les régions intermédiaires des Andes Arides (-0.28 ± 0.18 m w.e. a-1). Pour la première fois à l'échelle des Andes, une tendance inter-décennale de la perte volumique a été mise en évidence. Les taux d'amincissement des glaciers tropicaux et ceux situé sous 45°S sont négatifs et stables sur la période considérée. Cependant, alors que les glaciers des Andes arides sont proche de l'équilibre dans les années 2000, leur taux d'amincissement augmentent drastiquement à partir de 2010, coïncident ainsi avec une période de sécheresse intense depuis 2010. L'étude des contributions des pertes de masse décennales des glaciers aux débits des rivières révèle que la fonte de ces glaciers a en partie aidé à minimiser les impacts négatifs de cette sécheresse dans les Andes arides. Les résultats obtenus au cours de cette thèse apportent une meilleure compréhension des pertes récentes des glaciers Andins, localement et régionalement
Andean glaciers are amongst the fastest shrinking and the largest contributors to sea level rise in the world. They also represent crucial water resources in the vast semi-arid portions of this large Andes Cordillera (10°N-56°S), sustaining river runoff during dry periods and buffering the effects of droughts. Despite the widespread shrinkage of these glaciers, direct measurement of glacier fluctuations in the Andes are sparse, short-termed and in many cases incomplete, preventing the accurate quantification of recent ice loss for the entire mountain range. Comprehensively quantifying the magnitude of this loss at different special scales is crucial to better constrain future economical, ecological and social impacts. First, we evaluated the performance of a methodology to calculate glacier mass changes on Andean glaciers using time series of digital elevation models (DEMs) derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) stereo images. Over our validation zone, the Northern Patagonian Icefield, we found strongly negative icefield-wide mass balance rates of -1.06 ± 0.14 m w.e. yr-1 for the period 2000-2012, in good agreement with estimates from earlier studies and with a second independent estimate (-1.02 ± 0.21 m w.e. yr-1) obtained by differencing the better resolved Shuttle Radar Topography Mission (SRTM) DEM with a Satellite pour l'Observation de la Terre 5 (SPOT5) DEM. Importantly, this work permitted us to (i) validate "ASTER monitoring Ice towards eXtinction" (ASTERIX) method over the Andes; (ii) confirm the lack of penetration of the C-band SRTM radar signal into the NPI snow and firn except for a small high altitude region (above 2900 m a.s.l.) with negligible effects on NPI-wide mass balance; and (iii) provide the basis for an analysis of NPI mass balance changes during different sub-periods between 1975 and 2016 using additional DEMs. Then, we processed more than 30000 ASTER DEMs to calculate the integrated volume of ice lost by Andean glaciers during the past two decades. Andes-wide mass loss amounts to -22.9 ± 5.9 Gt yr-1 (-0.72 ± 0.22 m w.e. yr-1) for the entire period (or -26.0 ± 6.0 Gt yr-1 including subaqueous losses). All regions show consistent glacier wastage, with the most negative mass balance rates in the Patagonian Andes (-0.78 ± 0.25 m w.e. yr-1) and Tropical Andes (-0.42 ± 0.24 m w.e. yr-1). Relatively moderate loss (-0.28 ± 0.18 m w.e. yr-1) is measured in the intermediate regions of the Dry Andes. The inter-decadal patterns of glacier mass loss is an important contribution of this work, observed for the first time at an Andes-wide scale. We observe steady thinning rates in the Tropics and south of 45°S. Conversely, glaciers from the Dry Andes were stable during the 2000s, shifting to drastic thinning rates during the 2010s, coinciding with conditions of sustained drought since 2010. The evaluation of the imbalanced glacier contribution to river discharge during these two decades revealed that glaciers partially helped to mitigate the negative impacts of this sustained drought in the Dry Andes. The results obtained in this thesis contribute to the understanding of recent Andean glacier evolution at a local, regional and Andes-wide scale. We provide a high-quality, multi-decadal dataset that will be useful to constrain the diversity of present 21st century Andes-wide mass loss estimates, in the pursuit of the good calibration of glaciological and hydrological models intended to project future glacier changes and to improve water resource management in the Andes

Styles APA, Harvard, Vancouver, ISO, etc.

38

Khedekar, Mayur. « Temperature Based Estimation of the Time-Resolved Massflux of ICE Exhaust Gas Flow ». Thesis, KTH, Skolan för industriell teknik och management (ITM), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-300050.

Texte intégral

Résumé :

The aim ofthe study was to provideinformation and experience gained with fine wire thermocouples (TCs)or resistance wire thermometers (RWTs) temperature signals to estimate the timeresolved heat transfercoefficient. Constant current method was assumed in the study and medium used in this study was air. Here the heat balance equation has been described, different Nucorrelations and further discusses potential hurdles and difficulties one may encounter while calculating heat transfer coefficient. As asolution, the use of an appropriate heatbalance equation and lowpass filter was suggested as this provides a more accurate fitting. The investigation was carried out for Reynolds number (Re) 103 to 107 and Prandlt number (Pr) 0.734. The impact of the Re and Pr on the Nusselts number (Nu) around a cylinder was represented and all the results were compared with GT-POWER engine simulation software.
Syftet med studien var att tillhandahålla information och erfarenhet från fina trådtermoelement (TC) eller motståndstrådstermometrar (RWT) temperatursignaler för att uppskatta den tidsupplösta värmeöverföringskoefficienten. Metoden med konstant flöde antogs i studien och mediet som användes i denna studie var luft. Här har värmebalansekvationen beskrivits, olika Nu-korrelationer och diskuterat ytterligare potentiella hinder och svårigheter man kan stöta på vid beräkning av värmeöverföringskoefficienten. Som en lösning föreslogs användning av en lämplig värmebalansekvation och lågpassfilter eftersom detta ger en mer exaktpassform. Undersökningen genomfördes för Reynoldsnummer (Re) 103 till 107 och Prandlt nummer (Pr) 0,734. Effekten av Re och Pr på Nusselts-numret (Nu) runt en cylinder representerades och alla resultat jämfördes med GT-POWER-motorns simuleringsprogram.

Styles APA, Harvard, Vancouver, ISO, etc.

39

Viani, Alessandra. « Fonctionnement hydro-glaciologique du bassin versant de l'Arve dans les Alpes françaises : variabilité climatique et sur la disponibilité de la ressource en eau ». Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAU015/document.

Texte intégral

Résumé :

La réduction du volume des glaciers et la fusion printanière plus précoce de la neige causée par le réchauffement climatique provoquent des variations du cycle hydrologique à la fois pour les têtes de bassin versant, mais aussi pour les zones situées plus à l’aval. Afin de prédire correctement l’amplitude des changements possibles futurs et d’envisager une gestion adaptée, une bonne connaissance de l’interaction entre les glaciers, le climat et les écoulements hydriques est nécessaire. L’objectif de cette étude est d’évaluer l’effet de la variabilité climatique sur le fonctionnement hydro-glaciologique et ses conséquences sur la disponibilité de l’eau du bassin versant de l’Arve (Alpes françaises) depuis 1960. Ce bassin s’étend sur une surface de 1958 km2 et est composé de cinq bassins versants emboités (Arveyron d’Argentière, Arveyron de la Mer de Glace, Arve au Pont des Favrands, à Sallanches and au Bout du Monde), tous influencés par la fusion glaciaire et nivale mais dans différentes proportions étant donnée la large gamme d’extension de couverture glaciaire s’étalant de 5 á 53%. Ce travail est basé sur des longs jeux de données glaciologiques, météorologiques, hydrologiques et de couverture de neige qui sont issues soit de mesures ponctuelles dans l’espace soit de données obtenues par télédétection.L’analyse des tendances a été réalisée sur des données hydrologiques et météorologiques des cinq bassins versants emboités. Pour cela, le cycle saisonnier du débit est ajusté en utilisant une fonction mathématique de type “modèle à pic asymétrique”. Les changements observés des débits ont été reliés aux variables météorologiques ainsi que à l’évolution de la couverture glaciaire. Les résultats indiquent un comportement contrasté entre les bassins versants selon les taux d’englacements, avec une tendance croissante des valeurs de débit dans les bassins versants fortement englacés (couverture de glacier >30%) et une décroissante pour les moins englacés. La sensibilité du cycle hydrologique au changement climatique futur a été évaluée. Pour le milieu du 21e siècle, on prévoit que le volume annuel écoulé serait réduit de 16% pour l’Arveyron d’Argentière et de 31% pour l’Arveyron de la Mer de Glace. Pour la période estivale, la quantification détaillée de chaque terme de l’équation du bilan hydrologique, ainsi que leurs incertitudes, sur les bassins versants de l’Arveyron d’Argentière et de l’Arveyron de la Mer de Glace-Leschaux a permis de souligner l’importance des transferts d’eau souterraine pour représenter et prédire le comportement hydro-glaciologique d’un bassin versant donné. Deux model d’écoulement distribués de type degré-jour couples à un modèle de routage hydrologique à réservoir linéaire ont était utilisé sur le bassin versant de l’Arveyron d’Argentière sur la période 1960–2009. La calibration est effectuée autant sur la base des données de débit qu’avec une approche multicritère avec les données de débit, de couverture neigeuse et du bilan de masse annuel, à pas de temps journalier. Les résultats montrent l’aptitude d’utiliser un modèle classique degré-jour pour simuler le comportement hydro-glaciologique et la production d’eau sous-glaciaire d’un bassin versant fortement glaciaire. Pour la période 1960–2004, une valeur de Kling Gupta Efficiency de 0.85 entre le débit simulé et observe à était obtenu. La calibration multicritère semble réduire les incertitudes des simulations
Glacier recession and the anticipation of spring snow melt driven by a warming climate could lead to changes in the hydrological cycle affecting not only the headwater catchments but also the areas downstream. In order to correctly predict the magnitude of future possible changes and to consider appropriate strategies of water management, a good understanding of the interaction between glaciers, climate and hydrology is needed. The aim of this study is to assess the effect of climate variability on the hydro-glaciological behaviour and its consequence on water availability in the Arve River catchment (French Alps) since 1960. It covers 1958 km2 and is composed by five nested catchments (Arveyron d’Argentière, Arveyron de la Mer de Glace, Arve at Pont des Favrands, Arve at Sallanches and Arve at Bout du Monde), all influenced by glacier and snow melt but characterized by various percentages of glacier cover ranging from 5 to 53%. This research is based on a long dataset of in situ or remote sensing glaciological, meteorological, hydrological and snow cover area data.Trend analyses are performed on the hydrological and meteorological data at all the considered sites. The seasonal cycle of each catchment is fitted using a mathematical function, namely the asymmetric peak model, and changes in the discharge are related to observed changes in the meteorological variables and the glaciers’ evolution. Results point out a contrasting behaviour among the catchments characterized by different glacier covers, showing an increasing trend on the discharge values in highly glacierized catchments (with a glacier cover >30%) and a decrease in the low glacierized ones. The sensitivity of the seasonal cycle to the future climate is evaluated. In the mid-21st century the annual runoff would be reduced by 16% for Arveyron d’Argentière and 31% for Arveyron de la Mer de Glace. Over the summer season, a detailed quantification of each term of the hydrological balance equation, as well as their uncertainties, on the Argentière and Mer de Glace-Leschaux drainage basins allows to underline the importance of considering the groundwater transfers to represent and predict the hydro-glaciological behaviour of a considered catchment. Two different distributed temperature index melt models coupled with a linear reservoir discharge model are used on the Arveron d’Argentière catchment over the 1960–2009 period. The calibration is carried out against discharge only and with a multi- criteria approach considering the discharge, the snow cover area and the glacier-wide annual mass balance values at daily time step. Results demonstrate the suitability of the use of a classical degree day model in simulating the hydro-glaciological behaviour and the subglacial water production of a highly glacierized catchment. A KGE of 0.85 is obtained between the observed and simulate discharge values over the 1960–2004 period. The use of a multi-criteria approach seems to reduce the simulation uncertainties

Styles APA, Harvard, Vancouver, ISO, etc.

40

Reznichenko, Natalya. « Rock Avalanches on Glaciers : Processes and Implications ». Thesis, University of Canterbury. Geological Sciences, 2012. http://hdl.handle.net/10092/6524.

Texte intégral

Résumé :

This thesis examines the role of rock avalanches in tectonically active terrains including the effects of the deposits on glacier behaviour and their contribution to moraine formation. The chronologies of mountain glacier fluctuations, based on moraine ages, are widely used to infer regional climate change and are often correlated globally. In actively uplifting mountain ranges rock avalanches that travel onto the ablation zone of a glacier can reduce ice-surface melting by insulating the ice. This can cause buried ice to thicken due to slower ablation and can signiﬁcantly alter the overall glacier mass balance. This glacier response to supraglacial rock avalanche deposits can confound apparent climatic signals extracted from moraine chronologies. This thesis investigates the processes through which rock avalanche deposits may affect glaciers and develops a new technique to identify the presence of rock avalanche debris in glacial moraines. From laboratory experiments on the effects of debris on ice ablation it is demonstrated that the rate of underlying ice ablation is controlled by diurnal cyclicity and is amplified at high altitude and in lower latitudes. The relatively low permeability of rock avalanche sediment in comparison with non-rock avalanche supraglacial debris cover contributes to the suppression of ablation, at least partly because it greatly reduces the advection of heat from rain water to the underlying ice. The laboratory findings are supplemented by field investigations of two recent rock avalanche deposits on glaciers in the Southern Alps of New Zealand. This work demonstrates that the rock avalanche deposits are very thick (10 m at Aoraki/Mt. Cook and 7m at Mt. Beatrice) and almost stopped the ablation of the overlying ice. This resulted in the formation of an ice-platform more than 30 m high. This led to a reduction of the existing negative mass balance of the affected Tasman and Hooker Glaciers. There was little noticeable alteration of the overall glacial regime due to the small scale of the debris covered area (4 and 1% of the ablation zones for the Tasman and Hooker Glaciers, respectively) but there is a significant contribution to supraglacial debris, which is passively transported toward the terminus. A conceptual model of the response of mountain valley glaciers to emplacement of extensive rock avalanche debris on the ablation zone has been proposed for the effect of this type of debris on terminal moraine formation based on enhanced ‘dumping’ of supraglacial sediments. A new technique has been developed to distinguish rock-avalanche-derived sediment from sediment of glacial origin, based on the sedimentary characteristics of the finest fraction. Examination of rock avalanche sediment under the Scanning Electron Microscope showed that finer particles tend to form strong clumps, which comprise many smaller (down to nanometre-scale) clasts, named here ‘agglomerates’. These agglomerates are present in the ﬁne fraction of all examined rock avalanche deposits and absent in known non-rock-avalanche-derived glacial sediments. The agglomerates are characteristics of sediment produced under the high-stress conditions of rock avalanche emplacement and contrast with lower-stress process sub- and en-glacial environments. It is demonstrated that these agglomerates are present in some moraines in the Southern Alps of New Zealand that have been attributed to climate fluctuation. Consequently, this technique has the potential to resolve long-standing arguments about the role of rock avalanches in moraine formation, and to enhance the use of moraines in palaeoclimatological studies.

Styles APA, Harvard, Vancouver, ISO, etc.

41

Balland, Laurent. « Contribution à l'estimation des paramètres cinétiques et énergétiques de systèmes chimiques en milieux homogène et hétérogène dans un réacteur calorimétrique ». Rouen, 1997. http://www.theses.fr/1997ROUES054.

Texte intégral

Résumé :

Le présent travail propose une méthodologie pour estimer les paramètres cinétiques et thermiques de modèles de comportement énergétique de milieux réactionnels chimiques dans des conditions de synthèse aussi proches que possible des conditions industrielles. Des réactions chimiques, accompagnées de phénomènes physiques tels que la solubilisation ou le mélangeage de réactifs, sont réalisées dans un réacteur calorimétrique (RC1 de Mettler (R)) qui détermine la puissance expérimentale dégagée par le milieu. La méthode consiste à ajuster les paramètres du modèle reproduisant ce même dégagement de puissance. Un modèle incluant le transfert de matière couplé a la réaction chimique prend en compte la miscibilité progressive du réactif introduit. Dans le cas des réactions sans solvant, la variation du comportement du milieu réactionnel, au fur et à mesure de l'avancement de la réaction, est considérée selon trois approches. La première repose sur un modèle phénoménologique global et donne des résultats satisfaisants mais d'application limitée. Une deuxième approche, consistant à remplacer les concentrations par les activités dans les équations cinétiques, n'a pas abouti à des résultats concluants. La troisième approche prend en compte de manière beaucoup plus précise : l'aspect énergétique, en déterminant les enthalpies molaires d'excès du mélange forme par les réactifs et les produits ; l'aspect cinétique, en approfondissant le mécanisme chimique. Cette dernière approche fournit des résultats plus précis et extrapolables. Des méthodes spécifiques d'estimation ont été mises au point en couplant des méthodes globalement convergentes et localement convergentes : un maillage simple de l'espace des paramètres et un algorithme génétique fournissent des points d'initialisation pour une méthode de Rosenbrock. Les modèles sont transcrits au sein d'un logiciel développé en langage C++ sous environnement Windows (TM).

Styles APA, Harvard, Vancouver, ISO, etc.

42

Gardner, Alex Sandy. « Surface mass balance of Arctic glaciers : Climate influences and modeling approaches ». Phd thesis, 2010. http://hdl.handle.net/10048/1250.

Texte intégral

Résumé :

Land ice is losing mass to the worlds oceans at an accelerated rate. The worlds glaciers contain much less ice than the ice sheets but contribute equally to eustatic sea level rise and are expected to continue to do so over the coming centuries if global temperatures continue to rise. It is therefore important to characterize the mass balance of these glaciers and its relationship to climate trends and variability. In the Canadian High Arctic, analysis of long-term surface mass balance records shows a shift to more negative mass balances after 1987 and is coincident with a change in the mean location of the July circumpolar vortex, a mid-troposphere cyclonic feature known to have a strong influence on Arctic summer climate. Since 1987 the occurrence of July vortices centered in the Eastern Hemisphere have increased significantly. This change is associated with an increased frequency of tropospheric ridging over the Canadian High Arctic, higher surface air temperatures, and more negative glacier mass balance. However, regional scale mass balance modeling is needed to determine whether or not the long-term mass balance measurements in this region accurately reflect the mass balance of the entire Canadian High Arctic. The Canadian High Arctic is characterized by high relief and complex terrain that result in steep horizontal gradients in surface mass balance, which can only be resolved if models are run at high spatial resolutions. For such runs, models often require input fields such as air temperature that are derived by downscaling of output from climate models or reanalyses. Downscaling is often performed using a specified relationship between temperature and elevation (a lapse rate). Although a constant lapse rate is often assumed, this is not well justified by observations. To improve upon this assumption, near-surface temperature lapse rates during the summer ablation season were derived from surface measurements on 4 Arctic glaciers. Near-surface lapse rates vary systematically with free-air temperatures and are less steep than the free-air lapse rates that have often been used in mass balance modeling. Available observations were used to derive a new variable temperature downscaling method based on temperature dependent daily lapse rates. This method was implemented in a temperature index mass balance model, and results were compared with those derived from a constant linear lapse rate. Compared with other approaches, model estimates of surface mass balance fit observations much better when variable, temperature dependent lapse rates are used. To better account for glacier-climate feedbacks within mass balance models, more physically explicit representations of snow and ice processes must be used. Since absorption of shortwave radiation is often the single largest source of energy for melt, one of the most important parameters to model correctly is surface albedo. To move beyond the limitations of empirical snow and ice albedo parameterizations often used in surface mass balance models, a computationally simple, theoretically-based parameterization for snow and ice albedo was developed. Unlike previous parameterizations, it provides a single set of equations for the estimation of both snow and ice albedo. The parameterization also produces accurate results for a much wider range of snow, ice, and atmospheric conditions.

Styles APA, Harvard, Vancouver, ISO, etc.

43

Chi, Zhaohui 1982. « Investigation of Glacial Dynamics in the Lambert Glacier-Amery Ice Shelf System (LAS) Using Remote Sensing ». Thesis, 2012. http://hdl.handle.net/1969.1/148137.

Texte intégral

Résumé :

Numerous recent studies have documented dynamic changes in the behaviors of large marine-terminating outlet glaciers and ice streams in Greenland, the Antarctic Peninsula, and West Antarctica. However, fewer observations of outlet glaciers and ice shelves exist for the East Antarctic Ice Sheet. In addition, most recent surface velocity mappings of the Lambert Glacier-Amery Ice Shelf system (LAS) are derived for the time period of 1997-2000. From this research, surface velocity measurements provide a more extended view of the behavior and stability of the LAS over the past two decades than can be gleaned from a single observational period. This study uses remote sensing to investigate whether significant changes in velocities have occurred from the late 1980’s through the late 2010’s and assesses the magnitude of mass balance changes observed at the grounding line. To accomplish this goal, surface velocities of the LAS from late 1980’s to late 2010’s for three separate time periods are measured. The observed surface velocities of the LAS ranged from 0 to 1300 m yr^-1 during 1988-1990. A slight slowing down is detected in the central Amery Ice Shelf front by analyzing the surface velocity measurements made along the centerlines. The mass balance is the difference between snow accumulation and the outflux of the grounded LAS and is calculated for individual sub-basin during the three time intervals of 1988-1990, 1999-2004, and 2007-2011 to illustrate the mass balance variation under sub-basin level. The flux gates of the Lambert Glacial sub-basin combined with the Mellor Glacial and the Fisher Glacial sub-basin appear to be the largest outlet of the grounded ice of the LAS. The ice mass transported from the interior region through the three flux gates in total is 43.58 Gt yr^-1, 36.72 Gt yr^-1, and 38.61 Gt yr^-1 respectively for the three time intervals above. The sub-basins in the eastern side appear differently than the western side. The outfluxes of the eastern sub-basins vary from 15.85 to 18.64 Gt yr^-1, while the western outfluxes vary from 15.85 to 18.64 Gt yr^-1. The grounded LAS has discharged ice from 84.55 to 81.60 Gt yr^-1 and to 79.20 Gt yr^-1 during 1980s-1990s and 1990s-2000s. Assuming the snow accumulation distribution is stable, the grounded LAS mass lose has increased 2.95 Gt yr^-1 from 1980s to 1990s and 2.40 Gt yr^-1 from 1990s to 2000s. These results indicate insight into the stability of the Amery Ice Shelf over the last few decades.

Styles APA, Harvard, Vancouver, ISO, etc.

44

Wohlleben, Trudy Monique Heidi. « Ice-atmosphere interactions in the Canadian high Arctic : implications for the thermo-mechanical evolution of terrestrial ice masses ». Phd thesis, 2009. http://hdl.handle.net/10048/415.

Texte intégral

Résumé :

Canadian High Arctic terrestrial ice masses and the polar atmosphere evolve co-dependently, and interactions between the two systems can lead to feedbacks, positive and negative. The two primary positive cryosphere-atmosphere feedbacks are: 1) The snow/ice-albedo feedback (where area changes in snow and/or ice cause changes in surface albedo and surface air temperatures, leading to further area changes in snow/ice); and 2) The elevation - mass balance feedback (where thickness changes in terrestrial ice masses cause changes to atmospheric circulation and precipitation patterns, leading to further ice thickness changes). In this thesis, numerical experiments are performed to: 1) quantify the magnitudes of the two feedbacks for chosen Canadian High Arctic terrestrial ice masses; and 2) to examine the direct and indirect consequences of surface air temperature changes upon englacial temperatures with implications for ice flow, mass flux divergence, and topographic evolution. Model results show that: a) for John Evans Glacier, Ellesmere Island, the magnitude of the terrestrial snow/ice-albedo feedback can locally exceed that of sea ice on less than decadal timescales, with implications for glacier response times to climate perturbations; b) although historical air temperature changes might be the direct cause of measured englacial temperature anomalies in various glacier and ice cap accumulation zones, they can also be the indirect cause of their enhanced diffusive loss; c) while the direct result of past air temperature changes has been to cool the interior of John Evans Glacier, and its bed, the indirect result has been to create and maintain warm (pressure melting point) basal temperatures in the ablation zone; and d) for Devon Ice Cap, observed mass gains in the northwest sector of the ice cap would be smaller without orographic precipitation and the mass balance – elevation feedback, supporting the hypothesis that this feedback is playing a role in the evolution of the ice cap.

Styles APA, Harvard, Vancouver, ISO, etc.

45

Donoghue, SL. « Changes in the morphology, mass balance, and dynamics of Brown Glacier, Heard Island, with comparison to the surrounding sub-Antarctic islands ». Thesis, 2009. https://eprints.utas.edu.au/19886/1/whole_DonoghueShavawnLesley2009_thesis.pdf.

Texte intégral

Résumé :

Heard Island is located in one of the more isolated regions of the southern Indian Ocean at 53°06' S 73°30 E. There are 29 glacerised basins on Heard Island, which cover 70% of this 367 km2 island. Changes in the positions of Heard Island's glaciers, and by inference, changes in the region's climate, have been recorded only intermittently since the establishment of the first Australian base in 1947. In the 1950s the majority of these glaciers were stable or slightly thinning until a marked retreat began in the early 1960s. The retreat from the 1960s has continued through the last recorded observation in 2004. As of 1997, the glaciers on Heard Island had a total area of 257 km2 and an estimated volume of 14.2 km3. The limited climate records for the southern Indian Ocean have shown that there has been a +0.9° C (or +1.7° C 100a-1) change in temperature on Heard Island between 1947 and 2006, with similar increases in temperatures on the other sub-Antarctic islands (e. g., +2.7° C 100a-1 at Marion, +1.0° C 100a-1 at Kerguelen and +1.4° C 100a-1 at New Amsterdam islands). Additionally there has been a decrease in precipitation at Marion Island and Kerguelen since the late 1960s. The changes in air temperature and precipitation in the southern Indian Ocean over the last 60 years has had a significant effect of the glacier coverage on the region's islands. There have been dramatic changes in the extent of several glaciers observed on Marion, Crozet, Bouvetoya, and Kerguelen. The glaciers and semi-permanent snow cover on the more northern Marion and Crozet islands have disappeared completely since these islands were first discovered. Kerguelen Island glaciers have decreased in extent, with one of the original five regions disappearing completely. The limited observations on Bouvetoya indicates there has been only minor changes in it's glacier fronts. There are few observations of glacier front changes and even fewer glacier mass balance measurements on Heard Island. The changes in glacier front and climate for Brown Glacier, located on the northeastern coast of Heard Island, was determined by combining the climatic and physical characteristics that are measured on Heard Island, from 1950 to present. Ice core and crevasse samples were collected on Brown Glacier, on the northeast coast, in 2004 to determine the net balance from stratigraphic data and glaciochemical analysis. Oxygen isotope and trace ion were measured from ice cores and crevasses to observe any seasonal signals present in the ice and thereby determining the net balance. Although meltwater affected some of the sample sites a comparison with a low melt location, at 2450 m asl, reveals that melt effects are very site specific. Two non-melt affected sites, at elevations of 756 m and 920 m, provide an estimated net balance of 1.5 m w.e. Ablation was estimated from a combination of stake networks, downward looking sonars and a degree day model. A twenty stake central flowline network and downward looking sonars were deployed on Brown Glacier during the summers of 2000/01 and 2003/04 to measure the changes in the surface height. These measurements were compared to a degree day model for the ablation over the same period. The results indicated that in remote areas, degree day models can provide good estimates of the ablation when limited energy balance variables are available. The mass balance models for Brown Glacier indicate that an increase in temperature of 0.9° C between 1950 and 2001, and possibly a decrease in precipitation, has resulted in the retreat of the glacier. The steady state mass flux for 2001 indicates that if all of the current parameters remained constant then the terminus of Brown Glacier will retreat to an elevation of 350m. IPCC projections for 2090 were used to predict the changes that would occur on Brown Glacier if there was a further increase of temperature of 1.8 and 3.4° C. In both of these models Brown Glacier would cease to exist or possibly retreat to a small, semi-permanent snow field. This has similar implications for the other glaciers on Heard Island. Further increases in temperature and a continuation of the decreasing precipitation trends observed on the neighbouring sub-Antarctic islands implies that the smaller glaciers on Heard Island would also begin to retreat at a more rapid rate over the next 90 years. Glacier such as the Mary Powell, Nares, and Deacock that do not originate from high on the Big Ben Plateau are likely to retreat to elevation above —1000 m asl and the glaciers on the Laurens Peninsula will have disappeared completely.

Styles APA, Harvard, Vancouver, ISO, etc.

Thèses sur le sujet « Glacier mass balance estimation »

Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres