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Contributions from Salzburg
Daniel Hölbling has been one of STEC’s international collaborators and was involved with the programme since its inception. Daniel is the Head of the Risk, Hazard & Climate Research Group in the Department of Geoinformatics – Z_GIS at the Paris Lodron Universität Salzburg. Several of Daniel’s students have carried out projects in New Zealand, which involved applying a range of remote-sensing and image analysis techniques to erosion processes. Following are the abstracts of two recently completed projects.
Monitoring the evolution of the Kaiwhata landslide
Landslides are among the most serious geological hazards in mountainous and hilly areas of New Zealand, where they frequently cause significant damage and landscape changes. Monitoring the evolution of landslides and their consequences can help to mitigate hazards that could arise in later reactivation phases or in similar cases.
The abundance of time-series remote-sensing data has facilitated the mapping and monitoring of landslides. By applying object-based image analysis (OBIA) and using Sentinel-2 satellite data from 2017 to 2021, we set out to semi-automatically map the evolution of the Kaiwhata landslide and the subsequent impacts on the upstream area in the Wairarapa region of New Zealand. The OBIA mapping results revealed a gradual increase in the landslide area, with two major changes in June 2019 and November 2020. These major changes were followed by the formation of temporary landslide-dammed upstream lakes along the Kaiwhata River.
Pooladsaz K, Hölbling D, Brus J 2023. Monitoring the evolution of the Kaiwhata landslide in New Zealand using object-based image analysis and Sentinel-2 time series. GI-Forum Journal 11(2): 88–101. https://doi.org/10.1553/giscience2023_02_s88
Surface displacement of earthflows
This thesis provides insights into erosion processes and their effects on landscapes and ecosystems, especially erosion mechanisms such as earthflows. Changes in their morphology and surface are detected by satellite images, and image correlation and difference measurement is carried out through image-matching techniques based on normalised cross-correlation.
The project used the free stand-alone software CIAS (Correlation Image Analysis Software) developed by Andreas Kääb and Markus Vollmer in 2000. Erosion is a prominent geological process that shapes New Zealand's landscapes, and it is influenced by factors such as high rainfall, steep slopes, and human activities. The STEC programme has sought to enhance erosion management through comprehensive data collection, modelling, and analysis. Earthflows (slow-moving mass movements of fine-grained soils) pose significant challenges for environmental management due to their impacts on slope stability and downstream sedimentation. Remote-sensing techniques, particularly CIAS software, enable the large-scale monitoring of surface movements, providing insights into earthflow dynamics. Image matching techniques are well established for analysing surface velocity and measuring surface movement, and CIAS was used in various studies on glacier, landslide, and earthflow activity.
The project analysed earthflows near the Tiraumea, Ākitio, and Owahanga rivers using satellite data processed with CIAS software to reveal erosion patterns and temporal changes. Surface velocity measurements derived from PlanetScope satellite imagery were utilised to analyse displacement patterns, with statistical analyses revealing variations in movement characteristics across different earthflow areas. Despite methodological challenges and data limitations, this research contributed valuable insights into erosion dynamics. With the visualised results, the fields of movement and morphology of all three earthflows could be detected.
However, all the results were slightly noisy, and the values of correlation coefficients and the length of the shift vectors had wide ranges. In future studies images with less timespan should be tested to get better results and avoid scattered measurement results.
Bullmann L 2024. Analysis and measurement of surface displacements with CIAS on earthflows in the southeast of North Island, New Zealand. Unpublished MSc thesis, Paris Lodron Universität Salzburg, Salzburg, Austria.