Abstract. This study presents a reanalysis of the glaciologically obtained annual glacier mass balances at Hintereisferner, Ötztal Alps, Austria, for the period 2001–2011. The reanalysis is accomplished through a comparison with geodetically derived mass changes, using annual high-resolution airborne laser scanning (ALS). The grid-based adjustments for the method-inherent differences are discussed along with associated uncertainties and discrepancies of the two methods of mass balance measurements. A statistical comparison of the two datasets shows no significant difference for seven annual, as well as the cumulative, mass changes over the 10-year record. Yet, the statistical view hides significant differences in the mass balance years 2002/03 (glaciological minus geodetic records  = +0.92 m w.e.), 2005/06 (+0.60 m w.e.), and 2006/07 (−0.45 m w.e.). We conclude that exceptional meteorological conditions can render the usual glaciological observational network inadequate. Furthermore, we consider that ALS data reliably reproduce the annual mass balance and can be seen as validation or calibration tools for the glaciological method.

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 m a−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.

Digital terrain models (DTMs) are a standard data source for a variety of applications. DTM differencing is also widely used for detection and quantification of topographic changes. While several investigations have been made on the accuracy of DTMs, calculated from different kinds of input data, little has been published on the error of DTM differencing, specifically for the quantification of geomorphological processes. In this study, an extensive, multi‐temporal set of airborne laser scanning (ALS) data is used to investigate the accuracy of topographic change calculations in a high alpine environment, caused by different geomorphic processes. Differences from DTMs with cell sizes ranging from 0.25 m to 10 m were calculated and compared to very accurate point‐to‐point calculations for a variety of processes and in nearby stable areas which show no significant surface changes. The representativeness of the DTM differences is then compared to the terrain slope and surface roughness of the investigated areas to show the influence of these parameters on the errors in the differences. Those errors are then taken into account for analyses of the applicability of different cell sizes for the investigation of geomorphic processes with different magnitudes and over different time periods. The analyses show that the error of DTM differences increases with lower point densities and higher roughness and slope values. The higher the error, the greater the differences between two elevation datasets have to be in order to quantify certain morphodynamic processes. Lower point densities and higher roughness and slope values require greater process rates or longer time intervals in order to obtain valid results. Copyright © 2013 John Wiley & Sons, Ltd.

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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.