Reconstruction of morphometric changes over a decade in a high active alpine area using UltraCam aerial imagery.

High mountains represent one of the most dynamic environments on earth. Landscape changes are expressed by subtle movements such as creeping permafrost and slow landsliding, or sudden events, such as landslides, rockfalls, and debris flows, which extend over wide areas, imposing hazards to human life and infrastructure. Monitoring topographic changes in high mountains are paramount to understanding mass-transport systems, detecting related environmental variability, and assessing natural hazards. 

Due to the differences in the speed of topographic changes, monitoring high mountains requires high-resolution datasets over long periods of time and wide extents. Digital photogrammetry enables the computation of digital surface models (DSM) at various resolutions according to the scales of aerial photographs and has proved useful to monitor landscape changes in different geomorphological environments. High-resolution satellites provide long-time observations with wide coverage, but their resolution (1 m to 3 m) is often coarse to monitor small changes. On the other hand, UAV surveys, with a resolution as high as 1 cm, are limited to narrow areas. National mapping agencies have been performing digital aerial surveys at high-resolution (ca. 20 cm) for more than a decade, nevertheless, differences in acquisition technologies, lack of planning oriented to monitor geomorphological changes, uneven timestamps, and particularities of the individual surveys, pose challenges to the usage of these high-resolution datasets. 

The AlpSenseRely project, Alpine remote sensing of climate-induced natural hazards, aims to explore the feasibility of using aerial imagery to reconstruct morphometric landscape changes and establish a monitoring concept for alpine natural hazards.

The Hochvogel summit is located at 2 592 m a.s.l. at Allgäu High Alps, Germany/Austria. The Hochvogel’s southwestern slope is characterized by constant rockfall activity. Additionally, a meter-size-long fracture at the summit poses a catastrophic rock failure scenario (Leinauer et al., 2020, 2021). In 2016 a total of 130 000 m³ was detached from the southwestern slope of the summit and impacted the basin sediment mobilization and accumulation patterns. Observations on the basin response are key to understanding the response of the basin to sporadic high sediment input, relating environmental conditions, and constraining models of catastrophic events.

This contribution presents the retrospective topographic changes recorded at the Hochvogel slopes since 2010 in a total of seven UltraCam acquisitions at 20 cm resolution. We propose the usage of a 3D coregistration to improve the quantification of small sub-meter topographic changes. Eroded and sedimented volumes are computed for the ca. 400 000 m² southwestern basin using a fully free-source workflow based on python and semi-automatic filtering of errors. 

 

References:

Leinauer, J., Jacobs, B. and Krautblatter, M. (2020), “Anticipating an imminent large rock slope failure at the Hochvogel (Allgäu Alps)”, Geomechanics and Tunnelling, Vol. 13 No. 6, pp. 597–603.
Leinauer, J., Jacobs, B. and Krautblatter, M. (2021), “High alpine geotechnical real time monitoring and early warning at a large imminent rock slope failure (Hochvogel, GER/AUT)”, IOP Conference Series: Earth and Environmental Science, Vol. 833 No. 1, p. 012146.