There are considerable expenditures by government and private forest industry to enhance the growth of forests and reduce time required for crop rotation. The effectiveness of some of these treatments is dependent on site productivity. In addition, as responsible stewards of the forest resource and habitat, it is important that the state of forests are actively monitored, especially in the face of a changing climate and increased rates of disturbance. This dissertation reports on the development of a method for estimating and mapping forest productivity. The Shawnigan Lake thinning and fertilization forest installation, established in 1971 by CFS, was selected as the study site largely for its rich mensuration history. Square treatment plots were 0.04ha in area and included two thinning levels (1/3 & 2/3 of the basal area), two fertilization treatments (224kg & 448kg N/ha) with repeated fertilizations and macronutrient experiments (S, P) and control plots. A sample of plots was selected for high precision ground based lidar reference surveys. In September of 2012 a multi-sensor airborne survey of SLP was conducted that collected high-density lidar (up to ~70pnts/m2) and VNIR imaging spectroscopy. A thorough empirical radiometric calibration was conducted in addition to a spatial calibration at the Victoria International Airport. A combination of area based height percentile, point density ratios and statistical moments with individual lidar tree metrics including height distribution and proximity metrics were generated. Topographic metrics were also generated from the lidar ground classified point cloud. A library of spectral indices was computed from the imaging spectrometer data, with an emphasis on those indices known to be associated with vegetation health. These metrics were summarized to the plot level for a coarse scale regression analysis. A control survey and ground based lidar was used to facilitate an individual tree based fine scale of analysis, where reference data could unambiguously be matched to airborne collected data through the projected positions. Regression analysis was conducted applying the best subset regression with exhaustive feature selection search criteria and included a critical evaluation of the resulting selected features. Models were investigated considering the data source and in combination, that is, lidar metrics were considered independent of spectroscopy as well as the converse, and lidar metrics in combination with spectral metrics. The contribution of this study is the revelation that existing area based point cloud metrics are highly correlated, potentially noisy and sensitive to variations in point density, resulting in unstable feature selection and coefficients in model building. The approach offered as an alternative is the gridded lidar treetops method, which is evidently lacking within the literature and which this study overwhelmingly advocates. Additionally, the breadth and diversity of metrics assessed, the size and quality of the reference data applied, and the fine spatial scale of analysis are unique within the research area. This study also contributes to the knowledge base, in that, productivity can be estimated by remote sensing technologies. The use of gridded generalizations of the individual tree approach reduced estimation errors for both structural and productivity attributes. At the plot-level, crown structure and crown health features best estimated productivity. This study emphasizes the dangers of empirical modeling; at the even-aged SLP installation, growth is strongly tied to structure and the extrapolation to other sites is expected to provide biased values. It is my perspective that physical lidar structural models of the dominant and co-dominant crown classes be used to augment spatially explicit tree and stand growth models. In addition, direct measures should be obtained by multi-temporal lidar surveys or as an alternative photogrammetric point clouds after an initial lidar survey to quantify growth and aid in calibrating growth models. / Graduate

The main purpose of thesis is creation and evaluation of models for change detection of arable land to grassland by Hybrid-based Change Detection method, which combined approaches based on the Vegetation Indices, Image Differencing and Principal Component Analysis. Six locations with different seasonal configuration of images with high resolution and one locality covered by image with very high resolution were used. The areas were spread across the foothill areas of the Czech Republic. The selection of predictors and the most suitable model was supported by statistical calculation. Application selected models were carried out using a multi-temporal object classification and their accuracy were verified using reference data. The benefit of this thesis is finding generally applicable model useful to investigate the land cover change and evaluation of the potentially most appropriate seasonal configuration of images. Valuable is also methodology in this thesis which focus on selection of predictors and calculation the order of the most appropriate models, which is unique in the available literature. The thesis provides useful findings fitting to insufficiently explored issue of Change Detection arable land to grassland. Powered by TCPDF (www.tcpdf.org)

<p>Integrating unoccupied aerial systems (UAS) into agricultural remote sensing has revolutionized several domains, including crop yield estimation. This research arises from the need to combat citrus greening disease, a major threat to citrus production. Accurately estimating crop yields is crucial for evaluating the effectiveness of treatments and controls for this disease. In response, our study examined the efficacy of phenotypic data extracted from multi-temporal RGB and multispectral UAS images in estimating individual citrus tree yields before harvest and then using this as an indicator to analyze the effectiveness of the treatments and control choice.</p> <p>This study presents machine learning-based regression models for estimating individual citrus tree yields, utilizing the diverse features extracted to provide comprehensive insights into the citrus trees under investigation. Four machine learning algorithms, random forest regression, extreme gradient boosting regression, adaptive boosting, and support vector regression, were employed to build the yield estimation models. The experiment was designed in two phases: single-temporal and multi-temporal modeling.</p>

An integrating approach, including knowledge about whole systems of processes, is essential in order to reach both development and environmental protection goals. In this thesis Geographical Information Systems (GIS) are suggested as a tool to realise such integrated models. The main hypothesis in this work is that several natural technical and social systems that share a time-space can be compared and analysed in a GIS. My first objective was to analyze how GIS can support research, planning, and, more specifically, bring a broad scattering of competence together in an interdisciplinary process. In this process GIS was ivestigated as a tool to achieve models that give us a better overview of a problem, a better understanding for the processes involved, aid in foreseeing conflicts between interests, find ecological limits and assist in choosing countermeasures and monitor the result of different programs. The second objective concerns the requirement that models should be comparable and possible to include in other models and that they can be communicated to planners, politicians and the public. For this reason the possibilities to communicate the result and model components of multidimensional and multi-temporal data are investigated. Four examples on the possibilities and problems when using GIS in interdisciplinary studies are presented. In the examples, water plays a central role as a component in questions about development, management and environmental impact. The first articles focus on non-point source pollutants as a problem under growing attention when the big industrial and municipal point sources are brought under control. To manage non-point source pollutants, detailed knowledge about local conditions is required to facilitate precise advices on land use. To estimate the flow of metals and N(itrogen) in an area it is important to identify the soil moisture. Soil moisture changes over time but also significantly in the landscape according to several factors. Here a method is presented that calculate soil moisture over large areas. Man as a hydrologie factor has to be assessed to also understand the relative importance of anthropogen processes. To offer a supplement to direct measurements and add anthropogen factors, a GIS model is presented that takes soil-type, topography, vegetation, land-use, agricultural drainage and relative position in the watershed into account. A method to analyse and visualise development over time and space in the same model is presented in the last empirical study. The development of agricultural drainage can be discussed as a product of several forces here analyzed together and visualized with help of colour coded "Hyper pixels" and maps. Finally a discussion concerning the physiological and psychological possibilities to communicate multidimensional phenomena with the help of pictures and maps is held. The main conclusions in this theses are that GIS offer the possibilities to develop distributed models, e.g., models that calculate effects from a vide range of factors in larger areas and with a much higher spatial resolution than has been possible earlier. GIS also offer a possibility to integrate and communicate information from different disciplines to scientists, decision makers and the public. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1993, härtill 6 uppsatser.</p> / digitalisering@umu

Conselho Nacional de Desenvolvimento Científico e Tecnológico / The monitoring of the use and coverage is very important when studying determined regions, just because it helps knowing the environmental reality and contributes to solve problems that can probably appear. This research was done from the images of ALOS and LANDSAT satellites. Its main objective was to have a multi-temporal analysis of Arroio Grande micro watershed, central region of Rio Grande do Sul. The specific purposes were to identify and to quantify the different classes of land use found in this micro watershed along the 1987, 1998, 2002, 2005, 2007 and 2009 periods, as well as cross the land use information to show the forest coverage changes during the 22 years of analysis. The software SPRING 5.1.7 was employed to classify the supervised images through Bhattacharya, a sorter algorithm, and the map spatial analysis was done through the Spatial Language of Algebraic Geoprocessing program with the same computational application. The classes of land use as forest, field, agriculture, irrigated agriculture, exposed soil and water layer were observed in the images of each year in this analysis. These classes were utilized in the spatial analysis of the forest coverage in which forest monitoring parameters have been defined (forest maintenance and regeneration, deforestation). In this research the principal results that have been noticed were the increase of 17,98% on the distributed forest coverage, mainly in the areas of bigger declination, and the reduction of 16,32% on the field area. The analysis of the spatial forest coverage has presented stability with the landscape, in a gradual progression, because the area of forest maintenance, found in these 22 years, was 12.252,60ha, the forest regeneration was 4.389,12ha and only 1.853,82ha of deforested area. / O monitoramento do uso e cobertura da terra faz-se importante no estudo de determinadas regiões, pois auxilia no conhecimento da realidade ambiental e contribui na busca por soluções de problemas que possam se apresentar. A partir do uso de imagens dos satélites, ALOS e LANDSAT, foi realizada esta pesquisa com o objetivo principal de fazer uma análise multitemporal na microbacia do Arroio Grande, região central do Rio Grande do Sul, cujos objetivos específicos foram: Identificar e quantificar as diferentes classes de uso da terra encontradas na microbacia nos períodos de 1987, 1998, 2002, 2005, 2007 e 2009; além de cruzar as informações de uso da terra, evidenciando a cobertura florestal que sofreu alterações no decorrer dos 22 anos de análise. Para tanto, foram utilizados o software SPRING 5.1.7 para a classificação supervisionada das imagens, com a adoção do algoritmo classificador Bhattacharya, e a análise espacial dos mapas com a programação LEGAL do mesmo aplicativo computacional. Para esta análise, foram observadas as classes de uso do solo: floresta, campo, agricultura, agricultura irrigada, solo exposto e lâmina d água, nas imagens de cada ano. Estas classes foram empregadas na análise espacial da cobertura florestal em que foram definidos parâmetros para o monitoramento florestal (manutenção florestal, regeneração florestal e desmatamentos). Os principais resultados notados, nesta pesquisa, foram o aumento de 17,98% na cobertura florestal distribuída, principalmente, nas áreas de maiores declividade, e a redução de 16,32% sobre a área de campo. Quanto à análise espacial da cobertura florestal, esta mostrou-se em estabilidade com a paisagem, e em gradual progressão, pois a área de manutenção florestal encontrada, nestes 22 anos, foi de 12.252,60 ha, a regeneração florestal foi de 4.389,12 ha e apenas 1.853,82 ha de área desmatada.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This study had as objective to do a multi-temporal analysis from Arroio Grande watershed area, located in Santa Maria, RS, to detect the forest covering changes, its localization and quantification, as well as, to monitor the deforestation and regeneration processes and its main determinant factors. Four satellite images were used: LANDSAT 5 (1987), LANDSAT 5 (1995), LANDSAT 7 (2002) and CBERS 2 (2005). The SPRING applicative was used to elaborate the cartography dada basis and to digitally process the images. The images were segmented with threshold 10 to similarity and 20 to area and classified with Bhattacharya algorithm in the following land uses: forest, field, exposed soil, agriculture, irrigated agriculture and water lamina. After the images classification, a thematic maps cross was done with LEGAL programming. As a result, maps with the following land uses were obtained: forest maintenance, regeneration and deforestation. For a period of 18 years, the forest covering increased 25,59% or 10,24% in the area, mainly in the hillside and in the plateaus, changing from 14.135,42 ha (40,01%) in 1987 to 17.752,20 ha (50,25%) in 2005. However, there is still a great deficit of riparian forest in plain (depression), mainly due to rice cultivation. The obtained results show the potential of Remote Sensing and Geoprocessing techniques in mapping the land use. They also can be used to support researches, territorial planning, economical development and environmental preservation in this region. With the data bank obtained, it will be possible to create models able to simulate the forest covering dynamic in the studied area. / Este trabalho teve como objetivo realizar uma análise multitemporal da área da microbacia do Arroio Grande, localizada em Santa Maria, RS, a fim de detectar mudanças na cobertura florestal, sua localização e quantificação, além de monitorar os processos de desmatamento e regeneração e seus principais fatores determinantes. Foram utilizadas quatro imagens de satélite: LANDSAT 5 (1987), LANDSAT 5 (1995), LANDSAT 7 (2002) e CBERS 2 (2005). Utilizou-se o aplicativo SPRING para a elaboração da base de dados cartográficos e do processamento digital das imagens. As imagens foram segmentadas com limiar de 10 para similaridade e 20 para área e classificadas com auxílio do algoritmo Bhattacharya nos seguintes usos da terra: floresta, campo, solo exposto, agricultura, agricultura irrigada e lâmina d água. Após a classificação das imagens, foi realizado o cruzamento dos mapas temáticos com ajuda da programação LEGAL. Como resultado, obtiveram-se mapas com os seguintes usos da terra: manutenção florestal, regeneração e desmatamento, ou seja, o que permaneceu inalterado de uma época para outra, o que regenerou e o que foi desmatado. Para um período de 18 anos, a cobertura florestal aumentou 25,59% ou 10,24% da área da microbacia, principalmente na encosta (rebordo) e no planalto, passando de 14.135,42 ha (40,01%) em 1987 para 17.752,20 ha (50,25%) em 2005. Porém, ainda há um déficit muito grande de mata ciliar na planície (depressão), principalmente devido ao cultivo de arroz. Os resultados obtidos mostram o potencial das técnicas de Sensoriamento Remoto e Geoprocessamento no mapeamento do uso da terra. Também servem para apoiar as mais diversas iniciativas de pesquisa, planejamento territorial, desenvolvimento econômico e preservação ambiental nesta região. Com o banco de dados gerado, será possível confeccionar modelos capazes de simular a dinâmica da cobertura florestal na área pesquisada.

Les prés-salés sont des interfaces complexes entre le milieu continental et maritime d'une grande importance environnementale. En contexte de changement climatique, ces zones vulnérables font maintenant l'objet d'une attention particulière. Cette étude porte sur la mesure et la compréhension de la dynamique des prés-salés soumis à un régime méga-tidal (marnage supérieur à 10 m), à travers l'étude de deux estuaires des côtes du Nord-Ouest de la France : l'estuaire du Couesnon en baie du Mont-Saint-Michel (MSM) et l'estuaire de la Somme. L'originalité de l'approche est de considérer une très large gamme d'échelles temporelles, depuis l'échelle séculaire jusqu'à l'événement de marée. A l'échelle séculaire, la mesure de l'évolution de la surface des prés salés en Baie de Somme, à partir de documents historiques et de photos aériennes, montre une évolution étonnamment similaire à celle de l'estuaire du Couesnon depuis la canalisation de la partie terminale de ces rivières au milieu du XIXème siècle. Après une phase de développement rapide des prés salés, une réduction concomitante des taux de croissance est observée dans les deux estuaires au début du XXème siècle. Nous proposons que l'augmentation du niveau marin à cette période soit responsable de cette réduction de croissance des prés-salés. L'analyse pluriannuelle des surfaces en baie de Somme met en évidence des périodes d'érosion des prés-salés résultant de la migration des chenaux tidaux à la frontière des prés-salés. Une étude sur 3 ans en baie du MSM a permis de caractériser le fonctionnement d'un chenal tidal sinueux en frontière des prés salés, grâce à des mesures topographiques inédites réalisées avec un Lidar terrestre haute résolution, combinées à des mesures hydro-sédimentaires. Des relevés journaliers durant les marées d'équinoxe de Septembre et de Mars ont mis en évidence une relation très non-linéaire entre érosion des berges et hauteur de marée. Cette relation est régie principalement par une forte augmentation des vitesses du courant lors du jusant. L'étude des taux d'accrétion dans la partie interne du méandre tidal a révélé l'importance de la présence de la végétation pionnière. Des lois empiriques de sédimentation et d'érosion en fonction de la hauteur de marée sont proposées. Il est montré que 6 % des marées les plus hautes de l'année sont responsables de 90 % de l'érosion des prés-salés par migration du chenal, alors que la sédimentation est dominée par les marées les plus fréquentes. Ces travaux mettent en évidence le rôle fondamental de la divagation des chenaux en marge des prés salés méga-tidaux. Leur dynamique est contrôlée principalement par les marées les plus importantes, dont la fréquence est régit par des cycles nodaux de 4,4 à 18,6 ans. Les données topographiques et hydro-sédimentaires inédites acquises durant ce travail de thèse fournissent des contraintes fortes pour le développement de modèle d'évolution des prés salés. / Salt marshes are complex interfaces between land and sea of high environmental values. Theses vulnerable landforms are now subjected to particular attention since they are very sensitive to sea level changes and storm events. This study focuses on salt marsh dynamic subjected to a mega-tidal range (higher than 10 m) that received less attention, through the study of two estuaries of the north-western coast of France: The Couesnon estuary in the Bay of Mont -Saint-Michel and the Somme estuary. The originality of this study is to consider a wide range of time scales, from the secular one to tide events. At secular time scale, we measure the evolution of salt marsh surfaces in the Somme bay, from historical documents and aerial photographs. The comparison with the Couesnon estuary reveals a surprisingly similar evolution of salt marsh extension, since the derivation and embankment of their main river in early mid XIXth century. After a period of rapid salt marsh extension, a concomitant reduction of growth rates is observed in both estuaries in the early XXth century. We propose that the increase in sea level rise during this period is responsible for the reduced growth of salt marshes. The pluriannual analysis highlights periods of erosion of salt marshes resulting from the tidal channels migration on salt marsh fringe. However, the pluriannual time scale does not capture the processes governing the dynamics of channel migration. This has motivated a 3 years study of a sinuous tidal channel located on the fringe of the marsh with the aim to understand its dynamics at daily to annual scales. We have acquired 36 high resolution topographic surveys with Terrestrial Laser Scanner. We used daily surveys during spring tides of various High Water Level (HWL) to analyze channel dynamics at tidal event timescales. Daily TLS measurements revealed a non-linear relationship between bank erosion and tidal height. This relationship is related to a sharp increase in flow velocities during the ebb (up to 2.2 m/s) for overmarsh tides. Spatially averaged accretion on the inner bend tends to increase linearly with HWL and is increased by a factor 2 during summer/autumn spring tides at the peak of pioneer vegetation development. We propose empirical laws of sedimentation and erosion depending on the tide height, which model that 6% of the highest tides of the year are responsible for 90 % of salt marsh erosion by channel migration, while sedimentation is dominated by frequent tides. These results highlight the need to incorporate the influence of vegetation on sedimentation rates as well as tidal migration processes in models of salt marsh dynamic in mega-tidal environment. Long term modeling should account for the highest tides of the year, that make tidal channel very sensitive to the nodal cycle (18.6 years) which controls the occurrence of the highest tides in mega-tidal environment.

L'objet de ce projet de recherche est de prédire la durée de vie d'éléments mécaniques qui sont soumis à des phénomènes de fatigue cyclique. L'idée est de développer un schéma numérique novateur pour prédire la rupture de structures sous de tels chargements. Le modèle est basé sur la mécanique des milieux continus qui introduit des variables internes pour décrire l'évolution de l'endommagement. Le défi repose dans le traitement des cycles de chargement pour la prédiction de la durée de vie, particulièrement pour la prédiction de la durée de vie résiduelle de structures existantes. Les approches traditionnelles de l'analyse de la fatigue sont basées sur des méthodes phénoménologiques utilisant des relations empiriques. De telles méthodes considèrent des approximations simplificatrices et sont incapables de prendre en compte aisément des géométries ou des charges complexes associées à des problèmes d'ingénierie réels. Une approche basée sur la description de l'évolution thermodynamique d'un milieu continu est donc utilisée pour modéliser le comportement en fatigue. Cela permet de considérer efficacement des problèmes d'ingénierie complexe et la détérioration des propriétés du matériau due à la fatigue peut être quantifiée à l'aide de variables internes. Cependant, cette approche peut être numériquement coûteuse et, par conséquent, des approches numériques sophistiquées doivent être utilisées.La stratégie numérique sur laquelle ce projet est basé est singulière par rapport aux schémas incrémentaux en temps usuellement utilisés pour résoudre des problèmes élasto-(visco)plastique avec endommagement dans le cadre de la mécanique des milieux continus. Cette stratégie numérique appelée méthode LATIN (Large Time Increment method) est une méthode non-incrémentale qui recherche la solution de manière itérative sur l'ensemble du domaine spacio-temporel. Une importante innovation de la méthode LATIN est d'incorporer une stratégie de réduction de modèle adaptative pour réduire de manière très importante le coût numérique. La Décomposition Propre Généralisée (PGD) est une stratégie de réduction de modèle a priori qui sépare les quantités d'intérêt spacio-temporelles en deux composantes indépendantes, l'une dépendant du temps, l'autre de l'espace, et estime itérativement les approximations de ces deux composantes. L'utilisation de l'approche LATIN-PGD a montré son efficacité depuis des années pour résoudre des problèmes élasto-(visco)plastiques. La première partie de ce projet vise à étendre cette approche aux modèles incorporant de l'endommagement.Bien que l'utilisation de la PGD réduise les coûts numériques, le gain n'est pas suffisant pour permettre de résoudre des problèmes considérant un grand nombre de cycles de chargement, le temps de calcul peut être très conséquent, rendant les simulations de problèmes de fatigue intraitables même en utilisant les techniques LATIN-PGD. Cette limite peut être dépassée en introduisant une approche multi-échelle en temps, qui prend en compte l'évolution rapide des quantités d'intérêt lors d'un cycle et leur évolution lente au cours de l'ensemble des cycles. Une description type « éléments finis » en temps est proposée, où l'ensemble du domaine temporel est discrétisé en éléments temporels, et seulement les cycles nodaux, qui forment les limites des éléments, sont calculés en utilisant la technique LATIN-PGD. Puis, des fonctions de forme classiques sont utilisées pour interpoler les quantités d'intérêt à l'intérieur des éléments temporels. Cette stratégie LATIN-PGD à deux échelles permet de réduire le coût numérique de manière significative, et peut être utilisée pour simuler l'évolution de l'endommagement dans une structure soumise à un chargement de fatigue comportant un très grand nombre de cycles. / The motivation of the research project is to predict the life time of mechanical components that are subjected to cyclic fatigue phenomena. The idea herein is to develop an innovative numerical scheme to predict failure of structures under such loading. The model is based on classical continuum damage mechanics introducing internal variables which describe the damage evolution. The challenge lies in the treatment of large number of load cycles for the life time prediction, particularly the residual life time for existing structures.Traditional approaches for fatigue analysis are based on phenomenological methods and deal with the usage of empirical relations. Such methods consider simplistic approximations and are unable to take into account complex geometries, and complicated loadings which occur in real-life engineering problems. A thermodynamically consistent continuum-based approach is therefore used for modelling the fatigue behaviour. This allows to consider complicated geometries and loads quite efficiently and the deterioration of the material properties due to fatigue can be quantified using internal variables. However, this approach can be computationally expensive and hence sophisticated numerical frameworks should be used.The numerical strategy used in this project is different when compared to regular time incremental schemes used for solving elasto-(visco)plastic-damage problems in continuum framework. This numerical strategy is called Large Time Increment (LATIN) method, which is a non-incremental method and builds the solution iteratively for the complete space-time domain. An important feature of the LATIN method is to incorporate an on-the-fly model reduction strategy to reduce drastically the numerical cost. Proper generalised decomposition (PGD), being a priori a model reduction strategy, separates the quantities of interest with respect to space and time, and computes iteratively the spatial and temporal approximations. LATIN-PGD framework has been effectively used over the years to solve elasto-(visco)plastic problems. Herein, the first effort is to solve continuum damage problems using LATIN-PGD techniques. Although, usage of PGD reduces the numerical cost, the benefit is not enough to solve problems involving large number of load cycles and computational time can be severely high, making simulations of fatigue problems infeasible. This can be overcome by using a multi-time scale approach, that takes into account the rapid evolution of the quantities of interest within a load cycle and their slow evolution along the load cycles. A finite element like description with respect to time is proposed, where the whole time domain is discretised into time elements, and only the nodal cycles, which form the boundary of the time elements, are calculated using LATIN-PGD technique. Thereby, classical shape functions are used to interpolate within the time element. This two-scale LATIN-PGD strategy enables the reduction of the computational cost remarkably, and can be used to simulate damage evolution in a structure under fatigue loading for a very large number of cycles.

No description available.

Das aride Tarim-Becken im Nordwesten Chinas unterliegt Umweltveränderungen, die durch rapide Ausbreitung bewässerter Landwirtschaft sowie Klimawandel angetrieben sind. Während im Oberlauf in den letzten 50 Jahren ein Abflussanstieg beobachtet wurde, haben landwirtschaftliche Aktivitäten im Mittel- und Unterlauf zur Wasserknappheit und der drastischen Verkürzung des endorheischen Flusses geführt. Der Abfluss des Tarim, dessen Hauptzufluss der in Kirgistan entspringende Aksu-Fluss darstellt, wird zu einem großen Teil aus Schnee- und Gletscherschmelze in den oberen Gebirgseinzugsgebieten des Tien Shan gespeist. Da die Unterlieger von dem Wasser des Tarim zur Bewässerung in der Landwirtschaft abhängig sind, sind das Wissen über den Beitrag der Gletscherschmelze zum Abfluss sowie das Wissen über mögliche zukünftige Änderungen der Gletschermasse von großer Relevanz. Zahlreiche Studien beschränken sich oftmals nur auf die Betrachtung der Gletscherfläche, deren Änderung jedoch keine direkten Rückschlüsse auf etwaige Massenänderungen zulässt und zudem nur ein indirektes Signal für Klimaänderungen darstellt. Weiterführende Studien, welche zusätzlich Gletschermassenänderungen im Aksu-Einzugsgebiet untersuchen, haben häufig nur lokalen Charakter. Regionale Studien zu Massenänderungen, welche ganze Einzugsgebiete und Gebirgsketten umfassen, finden sich mehrheitlich für die letzte Dekade durch die Verfügbarkeit laseraltimetrischer Höhendaten und gravimetrischer Messungen, wobei letztere durch hohe Unsicherheiten gekennzeichnet sind. Um jedoch Aussagen hinsichtlich der zeitlichen Entwicklung der Gletscher treffen zu können, widmet sich die Arbeit insbesondere der Untersuchung von Gletschermassenveränderungen seit den 1970er Jahren unter Verwendung deklassifizierter amerikanischer Satellitenbilddaten, SRTM-Daten sowie SPOT-5-Stereodaten. Zur Ableitung geodätischer Gletschermassenbilanzen wurden Daten der Mapping Camera (MC) des Hexagon-Satelliten aus den Jahren 1973–1976 stereoskopisch ausgewertet und mit Daten der SRTM-Mission aus dem Jahr 2000 und SPOT-5-Stereodaten aus dem Jahr 2009 verglichen. Die Ableitung geodätischer Massenbilanzen aus multi-temporalen Geländemodellen erforderte deren Co-Registrierung auf das als SRTM gewählte Master-Modell. In einem zweistufigen Verfahren wurden Verkippungen über eine globale Trendfläche und horizontale Lagefehler über eine analytische Beziehung zwischen Oberflächenneigung, Orientierung und der entsprechenden Höhendifferenz unter Einbeziehung nicht-glazialer Pixel minimiert. Die Eindringtiefe des SRTM-C-Bands wurde mittels ICESat-Daten mit 2,2 m abgeschätzt und bei der Differenzbildung berücksichtigt. Zur Bereinigung der Differenzbilder zwischen den Geländemodellen wurde ein höhenbasierter Ansatz entwickelt, welcher eine abnehmende Varianz der Höhendifferenzwerte vom Ablations- zum Akkumulationsgebiet annimmt. Dieser Ansatz stellt eine deutlich realistischere Annahme im Vergleich zur oftmals verwendeten Nullannahme dar, welche von keinen Veränderungen in den Akkumulationsgebieten ausgeht. Die Gletscher im Aksu-Einzugsgebiet zeigten im Ergebnis einen Massenverlust von 0,35±0,34 m w.e./a im Zeitraum 1975–1999, was dem globalen Durchschnitt für diese Periode entspricht. In den Jahren 1999 bis 2009 wurde indes eine Abnahme des Massenverlusts (0,23±0,19 m w.e./a) festgestellt, was möglicherweise auf eine Zunahme des Niederschlags in der letzten Dekade zurückzuführen ist. Zudem zeigte sich, dass schuttbedeckte Gletscher, deren Schuttauflage ab einer Dicke von etwa 2 cm einen hemmenden Einfluss auf die Abschmelzrate hat, signifikant an Masse verloren haben bei gleichzeitig nur relativ geringer Flächenabnahme. Insgesamt wies die räumliche Verteilung der Massenänderungen eine starke Heterogenität auf, mit zunehmender Tendenz von Osten nach Westen und von den Innen- zu den Außenbereichen des Zentralen Tien Shan. Zusätzlich konnten zahlreiche, zuvor in der Literatur nicht benannte, surgende Gletscher identifiziert werden. Der durch Eismassenverlust induzierte Anteil am Gesamtabfluss des Aksu wurde im Ergebnis mit circa 20% ermittelt. Neben der Oberflächenneigung sind, in einfachen Modellen zur Eisdickenabschätzung, die basale Scherspannung und der Anteil basalen Gleitens an der Oberflächengeschwindigkeit Haupteinflussfaktoren. Anhand gemessener Eisdicken, fernerkundlich abgeleiteter Gletscherfließgeschwindigkeiten und der Oberflächenneigung, als Näherung der Neigung des Gletscherbetts, konnte ein empirischer Zusammenhang zur Abschätzung des Anteils basalen Gleitens abgeleitet werden. Die Eisdickenabschätzung für die vier größten Gletscher des Zentralen Tien Shan erfolgte im weiteren Verlauf durch Anwendung von Glen’s Fließgesetz, unter Annahme laminaren Fließens. Die Ergebnisse weisen für die betrachteten Gletscher mittlere Dicken von 70 m bis 140 m für deren schuttbedeckte Gletscherzungen auf. Diese Werte liegen teilweise deutlich unter denen bisheriger Studien, welche von einer globalen Scherspannung für den gesamten Gletscher oder einem konstanten Anteil basalen Gleitens ausgehen. Im Vergleich zu vorhandenen Eisdickenmessungen konnte durch die lokale Abschätzung der basalen Geschwindigkeit die mittlere Abweichung von zuvor mehr als 200 m auf etwa 50 m reduziert werden. Durch Einbeziehung der in der Arbeit ermittelten geodätischen Gletschermassenbilanzen wurde der relative Volumenverlust seit den 1970er Jahren mit 6% bis 28% quantifiziert, welcher deutlich unter dem schuttfreier Gletscher innerhalb Hochasiens liegt.