Advances in the process-related understanding of atmosphere-cryosphere-hydrosphere couplings on the Tibetan Plateau

Abstract HKT-ISTP 2013 B

Exploitation of TerraSAR-X Data for Land use/Land Cover Analysis Using Object-Oriented Classification Approach in the African Sahel Area, Sudan.

Recently, object-oriented classification techniques based on image segmentation approaches are being studied using high-resolution satellite images to extract various thematic information. In this study different types of land use/land cover (LULC) types were analysed by employing object-oriented classification approach to dual TerraSAR-X images (HH and HV polarisation) at African Sahel. For that purpose, multi-resolution segmentation (MRS) of the Definiens software was used for creating the image objects. Using the feature space optimisation (FSO) tool the attributes of the TerraSAR-X image were optimised in order to obtain the best separability among classes for the LULC mapping. The backscattering coefficients (BSC) for some classes were observed to be different for HH and HV polarisations. The best separation distance of the tested spectral, shape and textural features showed different variations among the discriminated LULC classes. An overall accuracy of 84 % with a kappa value 0.82 was resulted from the classification scheme, while accuracy differences among the classes were kept minimal. Finally, the results highlighted the importance of a combine use of TerraSAR-X data and object-oriented classification approaches as a useful source of information and technique for LULC analysis in the African Sahel drylands

Four decades of glacier variations at Muztagh Ata (eastern Pamir) : A multi-sensor study including Hexagon KH-9 and Pléiades data

Previous in situ measurements have indicated a slight mass gain at Muztagh Ata in the eastern Pamir, contrary to the global trend. We extend these measurements both in space and time by using remote sensing data and present four decades of glacier variations in the entire mountain massif. Geodetic mass balances and area changes were determined at glacier scale from stereo satellite imagery and derived digital elevation models (DEMs). This includes Hexagon KH-9 (year 1973), ALOS-PRISM (2009), Pléiades (2013) and Landsat 7 ETMC data in conjunction with the SRTM-3 DEM (2000). In addition, surface velocities of Kekesayi Glacier, the largest glacier at Muztagh Ata, were derived from amplitude tracking of TerraSARX images (2011). Locally, we observed strong spatial and temporal glacier variations during the last four decades, which were, however, on average not significant for the entire massif. Some south-west-exposed glaciers fluctuated or advanced, while glaciers with other aspects rather experienced continuous shrinkage. Several glaciers such as Kekesayi indicate no measurable change at their frontal position, but clear down-wasting despite mostly thick debris coverage at low altitudes. The surface velocity of this debriscovered glacier reach up to 20 cm per day, but the lowest part of the tongue appears to be stagnant. The low velocity or even stagnancy at the tongue is likely one reason for the down-wasting. On average, the glaciers showed a small, insignificant shrinkage from 274.3 ± 10.6 km2 in 1973 to 272.7 ± 1.0 km2 in 2013 (-0.02 ± 0.1%a-1). Average mass changes in the range of -0.03 ± 0.33mw.e. a-1 (1973-2009) to -0.01 ± 0.30mw.e. a-1 (1973-2013) reveal nearly balanced budgets for the last 40 years. Indications of slightly positive rates after 1999 (+0.04 ± 0.27 mw.e. a-1) are not significant, but confirmed by measurements in the field.Publisher PDFPeer reviewe

Repeated glacial lake outburst flood threatening the oldest Buddhist monastery in north-western Nepal

Since 2004, Halji village, home of the oldest Buddhist Monastery in north-western Nepal, has suffered from recurrent glacial lake outburst floods (GLOFs). A sudden englacial drainage of a supraglacial lake, located at a distance of 6.5 km from the village, was identified as the source of the flood. The topography of the lake basin was mapped by combining differential Global Positioning System (DGPS) measurements with a structure-from-motion (SFM) approach using terrestrial photographs. From this model the maximum filling capacity of the lake has been estimated as 1.06 ×10^6 m³ with a maximum discharge of 77.8 m³ s⁻¹, calculated using the empiric Clague–Mathews formula. A simulation of the flooded area employing a raster-based hydraulic model considering six scenarios of discharge volume and surface roughness did not result in a flooding of the village. However, both the village and the monastery are threatened by undercutting of the river bank formed by unconsolidated sediments, as it already happened in 2011. Further, the comparison of the GLOF occurrences with temperature and precipitation from the High Asia Reanalysis (HAR) data set for the period 2001–2011 suggests that the GLOF is climate-driven rather than generated by an extreme precipitation event. The calculation of geodetic mass balance and the analysis of satellite images showed a rapid thinning and retreat of Halji Glacier which will eventually lead to a decline of the lake basin. As the basin will persist for at least several years, effective mitigation measures should be considered. A further reinforcement of the gabion walls was suggested as an artificial lake drainage is not feasible given the difficult accessibility of the glacier

Evaluation of a distributed energy balance model for a high-altitude glacier on the Tibetan Plateau using glaciological measurements and a time-lapse camera system

Abstract HKT-ISTP 2013 B