Lorenzo Rieg

QUANTIFICATION OF GEOMORPHODYNAMICS IN GLACIATED AND RECENTLY DEGLACIATED TERRAIN BASED ON AIRBORNE LASER SCANNING DATA

Sailer, R., Bollmann, E., Hoinkes, S., Rieg, L., Sproß, M. and Stötter, J., 2012. Quantification of geomorphodynamics in glaciated and recently deglaciated terrain based on airborne laser scanning data. Geografiska Annaler, Series A: Physical Geography, 94, 17–32. doi:10.1111/j.1468‐0459.2012.00456.x ABSTRACT This article highlights the ability of airborne laser scanning (ALS) to detect, map and quantify geomorphological processes in high alpine environments. Since 2001, ALS measurements have been carried out regularly at Hintereisferner (Ötztal Alps, Tyrol, Austria), resulting in a unique data record of 18 ALS flight campaigns. The quantifications of volumetric earth surface changes caused by dead‐ice melting, fluvial erosion/deposition, rock‐fall activity, gravitational displacements and permafrost degradation in glaciated, recently deglaciated and periglacial terrain is based on the analysis of ALS point clouds (vector data) to preserve the high quality of the data. We present inter‐annual, annual and perennial trends of geomorpho‐dynamically induced topographic changes. The most significant changes occurred at two dead ice bodies (−0.48 m and −0.24 m respectively per year). At a complex rock fall site, mean annual vertical changes of −0.25 m are observed in the source area, respectively 0.25 m of deposited material in the run‐out area. Fluvial erosion processes are connected with subsequent gravitational denudation, reallocation and deposition. Topographic changes caused by fluvial erosion between 2001 and 2009 range from −0.68 m to −1.20 m. Surface elevation increase caused by fluvial accumulation is found to be 0.48 m from 2001 to 2009. Minor annual surface elevation changes (between −0.05 m and −0.10 ma−1) are detected in permafrost areas. Finally, the significance of the process‐dependent topographic change rates is assessed, regarding the accuracy of the ALS data, the magnitude of the process, the time lapse between the single ALS‐campaigns and disturbing factors (e.g. snow cover). For processes with high magnitudes time lapse rates can be shorter than one year and disturbing factors have only minor influences on the results. In contrast, results of processes with low magnitudes gain relevance with an increasing time lapse between the ALS campaigns, the frequency of flight campaigns and if disturbing factors can be excluded.

Pléiades Tri-Stereo Data for Glacier Investigations—Examples from the European Alps and the Khumbu Himal

In this study, we use Pléiades tri-stereo data to generate a digital elevation model (DEM) from the Pléiades images using a workflow employing semi-global matching (SGM). We examine the DEM accuracy in complex mountain glaciated terrain by comparing the new DEMs with an independent high-quality DEM based on airborne laser scanning (ALS) data for a study area in the Austrian Alps, and with ground control points for a study area in the Khumbu Himal of Nepal. The DEMs derived using the SGM algorithm compare well to the independent high-quality ALS DEM, and the workflow produces models of sufficient quality to resolve ground control points, which are based on Pléiades imagery that are of sufficient quality to perform high spatio-temporal resolution assessments of remote areas for which no field data is available. The relative accuracy is sufficient to investigate glacier surface elevation changes below one meter, and can therefore be applied over relatively short periods of time, such as those required for annual and seasonal assessments of change. The annual geodetic mass balance for the Alpine case derived from our DEM compares well to the glaciological mass balance, and multitemporal DEM analysis is used to resolve the seasonal changes of five glaciers in the Khumbu Himal, revealing that glaciological processes such as accumulation, ablation, and glacier movement mainly take place during the summer season, with the winter season being largely inactive in the year sampled.

Mass balance processes on glaciers in the Khumbu-Himal (Nepal) based on Pléiades tri-stereo data

In the presented study, we are using Pléiades tri-stereo data to analyse mass balance related processes on several debris-covered glaciers in the Khumbu-Himal region of Nepal. A focus is placed on the important but until now unquantified role of avalanche snow and the influence of rock debris cover on the glacier tongues and the ablation at exposed ice fliffs within the debris. High resolution digital terrain models will be extracted photogrammetrically from the Pléiades scenes, while the optical information will be used for pixel- and object-based surface classification in order to map surface features such as progrlacial lakes, avalance cones and ice-cliffs.