Cryosphere Applications

Synthetic aperture radar (SAR) provides large coverage and high resolution, and it has been proven to be sensitive to both surface and near-surface features related to accumulation, ablation, and metamorphism of snow and firn. Exploiting this sensitivity, SAR polarimetry and polarimetric interferometry found application to land ice for instance for the estimation of wave extinction (which relates to sub surface ice volume structure) and for the estimation of snow water equivalent (which relates to snow density and depth). After presenting these applications, the Chapter proceeds by reviewing applications of SAR polarimetry to sea ice for the classification of different ice types, the estimation of thickness, and the characterisation of its surface. Finally, an application to the characterisation of permafrost regions is considered. For each application, the used (model-based) decomposition and polarimetric parameters are critically described, and real data results from relevant airborne campaigns and space borne acquisitions are reported

Flow and Temperature Dynamics in the Hydrologic Response of Alpine Catchments: Travel Time Formulation and Geomorphologic Signatures

We present a travel time formulation of water and energy transport at sub-catchment scale. The derived equations are implemented in Alpine3D, a physically-based model of snow processes, which provides the necessary boundary conditions to perform hydro-thermal response simulations of Alpine catchments. The model set-up accounts for advective and non- advective energy fluxes to perform spatially distributed simulations of streamflow and temperature in river networks having an arbitrary degree of geomorphological complexity. The model gives reliable predictions of streamflow and tem- perature, as shown by comparing modeled and measured hydrographs and thermographs at the outlet of the Dischma catchment (45 km2) in the Swiss Alps. Our model setup is applied to investigate the role of hillslope aspects, representing the main control on radiation and snowmelt patterns, in the flow regime of the study catchment. The distributed simu- lation results show that snowmelt-induced discharge exhibits a visible geomorphologic signature of aspects at sub-catch- ment scale, but this progressively fades out going from headwater streams to the outlet. Accordingly, the geomorphologic signature is scale-dependent: it is significant at small scales where the high aspect correlation generates predominant orientations but is lost at larger scales where aspects are de-correlated and different orientations are averaged out. We further apply the model to investigate the geomorphologic signature of drainage density in the thermal regime of the study catchment. The results show that the contribution of the advective energy fluxes becomes progressively smaller when the drainage density increases, while the one of the non-advective energy fluxes becomes larger. Moreover, such variations balance out at the catchment outlet, where the temperature signal is not sensitive to the increasing drainage density. The relevance of the performed invetigations stems from the increasing scientific interest concerning the impacts of the warming climate on water resources management and temperature-influenced ecological processes

Evolution récente des glaciers du Pamir-Karakoram-Himalaya (apport de l'imagerie satellite)

La région du Pamir - Karakoram - Himalaya (PKH) constitue la plus grande réserve de glace terrestre après les régions polaires. Cependant, l'évolution récente de ces glaciers, indicateurs privilégiés du changement climatique en haute altitude, reste encore mal connue, du fait notamment de difficultés d'accès et de conditions climatiques qui rendent délicate l'acquisition de mesures in situ. L'objectif de cette thèse est de contribuer à l'amélioration des connaissances sur l'évolution globale des glaces du PKH au cours de la dernière décennie, en s'appuyant sur des images satellite et des modèles numériques de terrain (MNTs). Une premièreméthodologie a été développée pour assurer le suivi automatique de la distribution spatiale et de l'évolution temporelle des lacs glaciaires à partir d'images Landsat entre 1990 et 2009 sur sept zones d'études réparties le long du PKH. Ainsi, une certaine disparité des types, tailles et évolutions des lacs entre la partie orientale et occidentale du PKH a été mise en évidence. Sur la période de temps considérée, la superficie des lacs a légèrement diminué à l'ouest (Karakoram et Hindu Kush), a été en très nette augmentation à l'est (Népal et Bouthan) et relativement stable sur la partie centrale (Inde du nord-ouest). Le bilan de masse des glaciers a ensuite été calculé, à partir des variations d'épaisseurs mesurées en comparant deuxMNTs, acquis à deux dates différentes, et issus de lamission SRTM et du satellite SPOT5. Cette méthode implique un certain nombre de corrections et d'ajustements au préalable, afin de garantir des mesures les moins biaisées possible. Ainsi, la différence de résolution spatiale initiale des MNTs peut être à l'origine d'un biais fonction de l'altitude, de même que la pénétration des ondes radar de la mission SRTM dans la neige et la glace est à prendre en compte le cas échéant, pour ne pas sous-estimer les altitudes sur les glaciers. Là encore, on observe des disparités entre les différents bilans de masse régionaux sur la période 1999-2011, avec des pertes de masse modérées sur l'Himalaya central et oriental(-0.30+-0.08 m a-1 w.e.), plus accentuées sur l'Himalaya occidental (-0.43+-0.09 m a-1 w.e.) et des gains de masse plus à l'ouest, pour les glaciers des massifs du Pamir (+0.14+-0.11 m a-1 w.e.) et du Karakoram (+0.10+-0.20 m a-1 w.e.). Ces résultats confirment donc l'anomalie des glaciers du Karakoram et suggèrent des comportements similaires au Pamir. Le bilan de masse global des glaciers du PKH est estimé à -0.13+-0.06 m a-1 w.e.The Pamir - Karakoram - Himalaya (PKH) mountain range is considered to be the largest terrestrial ice reservoir outside polar regions. However, the recent evolution of these glaciers, recognized as valuable high-altitude climatic indicators, remains poorly known, mainly because of accessibility issues and harsh meteorologic conditions that hamper field work and in situ observations. The aim of this thesis is therefore to improve the knowledge of glacier changes in PKH and study their evolution over the past decade, based on satellite images and digital elevation models (DEMs). We first developed automatic classification algorithms to monitor the spatial distribution and temporal evolution of glacial lakes between 1990 and 2009 along the PKH, based on Landsat images. We thereby highlight different types, sizes and evolutions of glacial lakes between eastern and western PKH. During the study period the total glacial lake area slightly decreased in the west (Hindu Kush and Karakoram), greatly increased in the east (Nepal, Bhutan) and remained stable in the central part (north-west India). We then computed the mass balance of PKH glaciers from elevation changes measured by comparing two DEMs, acquired 10 years appart, by the SRTM mission and the SPOT5 satellite. This method relies on a precise relative adjustment (horizontal and vertical) of the DEMs to remove possible systematic biases within glacier elevation changes. The difference in the original spatial resolution of the DEMs can result in an elevation-dependent bias, as well as the radar penetration into snow and ice can seriously underestimate glacier elevation in the case of a DEM derived from radar data such as SRTM. The spatial pattern of regional glacier mass balances between 1999 and 2011 turns out to be contrasted, with moderatemass losses in eastern and central Himalaya (-0.30+-0.08m yr-1 w.e.), stronger in western Himalaya (-0.43+-0.09 m yr-1 w.e.) and mass gains further west, for Pamir(+0.14+-0.11 m yr-1 w.e.) and Karakoram glaciers (+0.10+-0.20 m yr-1 w.e.). The global mass balance of PKH glaciers is estimated at -0.13+-0.06 m yr-1 w.e.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF