Abstract
Abstract. Accurate and timely information on avalanche occurrence is key for avalanche warning, crisis management and avalanche documentation. Today such information is mainly available at isolated locations provided by observers in the field. The achieved reliability, considering accuracy, completeness and reliability of the reported avalanche events, is limited. In this study we present the spatially continuous mapping of a large avalanche period in January 2018 covering the majority of the Swiss Alps (12 500 km2). We tested different satellite sensors available for rapid mapping during the first avalanche period. Based on these experiences, we tasked SPOT6 and SPOT7 for data acquisition to cover the second, much larger avalanche period. We manually mapped the outlines of 18 737 individual avalanche events, applying image enhancement techniques to analyze regions in the shade as well as in brightly illuminated ones. The resulting dataset of mapped avalanche outlines, having unique completeness and reliability, is evaluated to produce maps of avalanche occurrence and avalanche size. We validated the mapping of the avalanche outlines using photographs acquired from helicopters just after the avalanche period. This study demonstrates the applicability of optical, very high spatial resolution satellite data to map an exceptional avalanche period with very high completeness, accuracy and reliability over a large region. The generated avalanche data are of great value in validating avalanche bulletins, in completing existing avalanche databases and for research applications by enabling meaningful statistics on important avalanche parameters.
Highlights
Information on the occurrence and runout of snow avalanches is a key parameter for the development of effective hazard mitigation approaches for settlements and traffic infrastructure (Rudolf-Miklau et al, 2014; Bühler et al, 2018)
Comprehensive information on avalanche activity is important for the evaluation of the avalanche bulletin, the European avalanche danger scale (Meister, 1994) and further developments of avalanche danger assessment tools such as the matrix of the European Avalanche Warning Services (EAWS; Müller et al, 2016) or the conceptual model of avalanche hazard (Statham et al, 2017)
The datasets were oriented using bundle block adjustment and orthorectified by swisstopo based on its high-quality digital elevation model (DEM) swissALTI3D with a spatial resolution of 2 m, which is available for the entire country of Switzerland
Summary
Information on the occurrence and runout of snow avalanches is a key parameter for the development of effective hazard mitigation approaches for settlements and traffic infrastructure (Rudolf-Miklau et al, 2014; Bühler et al, 2018). Optical data from airplanes and satellites with very high spatial resolution (0.1–0.5 m) were successfully applied to automatically map avalanche debris under cloud-free conditions (Bühler et al, 2009; Lato et al, 2012; Eckerstorfer et al, 2016; Korzeniowska et al, 2017) These datasets are only available for selected regions and are hard to get on short notice. The aim of this investigation is to generate a record of avalanche occurrences for an avalanche period over a large region (12 500 km2) with very high reliability This dataset can be used for a meaningful statistical analysis of the avalanche period and to produce a nearly complete database of avalanche runouts that can be applied to validate the avalanche bulletin and hazard maps.
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