The impact of terrain model source and resolution on snow avalanche modelling
- 1National School of Surveying, University of Otago, P.O. Box 56, Dunedin, New Zealand
- 2Downer NZ Ltd, Milford Road Alliance, Te Anau, New Zealand
- 3WSL Institute for Snow and Avalanche Research SLF, Flüelastrasse 11, 7260 Davos Dorf, Switzerland
- 4Climate Change, Extremes and Natural Hazards in Alpine Regions Research Center CERC, Flüelastrasse 11, 7260 Davos Dorf, Switzerland
- 5School of Geography, University of Otago, Dunedin, New Zealand
- 1National School of Surveying, University of Otago, P.O. Box 56, Dunedin, New Zealand
- 2Downer NZ Ltd, Milford Road Alliance, Te Anau, New Zealand
- 3WSL Institute for Snow and Avalanche Research SLF, Flüelastrasse 11, 7260 Davos Dorf, Switzerland
- 4Climate Change, Extremes and Natural Hazards in Alpine Regions Research Center CERC, Flüelastrasse 11, 7260 Davos Dorf, Switzerland
- 5School of Geography, University of Otago, Dunedin, New Zealand
Abstract. Natural hazard models need accurate digital elevation models (DEMs) to simulate mass movements on three-dimensional terrain. A variety of platforms (terrestrial, drones, aerial, satellite) and sensor technologies (photogrammetry, LiDAR, interferometric synthetic aperture radar) are used to generate DEMs at a range of spatial resolutions with varying accuracy. As the availability of high-resolution DEMs continues to increase and the cost to produce DEMs continues to fall, hazard modellers must often choose which DEM to use for their modelling. Here we use current state-of-the-art sensor technologies (satellite photogrammetry and terrestrial LiDAR) to generate high-resolution DEMs and test the sensitivity of the Rapid Mass Movements Simulation software (RAMMS) to the DEM source and spatial resolution for simulating a large and complex snow avalanche along Milford Road in Fiordland, Aotearoa New Zealand. Holding the RAMMS parameters constant while adjusting the source and spatial resolution of the DEM reveals how differences in terrain representation between the satellite photogrammetry and terrestrial LiDAR DEMs (2 m spatial resolution) affect the reliability of the simulation estimates (e.g., maximum core velocity, powder pressure, final debris pattern). At the same time, coarser representations of the terrain (5 m, 15 m spatial resolution) produce simulated avalanches that run too far and produce a powder cloud that is too large, though with lower maximum impact pressures, compared to the actual event. The complex nature of the alpine terrain in the avalanche path (steep, rough, rock faces, tree-less) made it a suitable location to specifically test the model sensitivity to digital surface models (DSMs) where both the ground and above-ground features on the topography are included in the elevation model. Combined with the nature of the snowpack in the path (warm, deep with a steep elevation gradient) lying on a bedrock surface and plunging over a cliff, RAMMS performed well in the challenging conditions when using the high spatial-resolution 2 m DSM.
Aubrey Miller et al.
Status: final response (author comments only)
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RC1: 'Comment on nhess-2022-97', Anonymous Referee #1, 25 Apr 2022
1) general comments
The manuscript investigates the influence of selected digital elevation models from different sources and resolutions on the modeling of a snow avalanche. Model runs and model output parameters are compared to a reference avalanche event. The manuscript could be improved by providing more information about the practical usability of the different model results and the transferability of findings.
2) specific comments
Abstract: Please note that digital elevation models are always a 2.5 D representation and not fully 3D.
Abstract: Please use the term “topographic LiDAR” throughout the whole paper.
Abstract: “performed well” - please add quantitative results in the abstract as well.
Line 189: Sections 1.4.2 climatic setting and 1.4.2 avalanche mitigation are not relevant for a study analyzing the effect of DEM resolution. Please delete or shorten.
Line 213: Please add a workflow diagram visualizing all processing and analysis steps providing a better overview for readers.
Line 219: What is the motivation to make use of the selected DEM sources? There are several other options, which would be also interesting for comparison e.g. why not making use of Pleiades tri-stereo, ASTER GDEM, etc. Please explain to the reader what DEMs are available for the specific site investigated and in New Zealand in general.
Line 237: Please add information about the resampling method and settings used instead of only naming the tool.
Line 251: Can you demonstrate the change in roughness without and with cleaning? How is this step reproducible or transferable to other sites?
Line 253: “other times of year”: Does the phenological stage of vegetation have any influence on the surface representation? You may demonstrate the effect at overlapping areas.
Line 259: “without coordinate transformation” - Please specify. What coordinate system would be used in this case? How can you be sure that your point cloud model is oriented along with the horizontal and vertical axis correctly?
Table 1: Please specify acquisition dates for TLS scans.
Line 284: “interpolation” – please specify the interpolation strategy and settings used and document the influence on DEM quality.
Line 292: Please provide quantitative information on “required less hole-filling”.
Line 306: Is the code of your developed script somewhere available for the scientific community?
Line 327: Please quantify “better represent the true terrain”.
Line 331: Please explain and motivate your decision using two snow layers in the model. How did the weather station data look like so that you decided for a two layer setting?
Line 344: Please list all model parameters and input data sets used in different test runs, e.g. in a table as an appendix.
Line 360: Please add values for co-registration quality.
Line 376: You estimate a reference volume derived from TLS and PlanetScope. Can you add information on how safe this value is considering the resolution and uncertainty of input data sets and preprocessing steps? What deviation would you allow from this reference value interpreting a model result still as correct?
Line 378: What do we learn from the mass values for the tests performed in this study? Are they relevant?
Line 379: Please explain avalanche classification “size 5” in more detail.
Line 380: Please link avalanche properties mentioned here to the results in Table 2.
Fig. 5: Please add elevation profile lines in the two maps (subfigures upper and lower right).
Line 388: Here authors explain the special nature of the topographic situation of the site investigated. Are the results of the study transferable to other topographic situations? Can you please add information on the transferability and generalization of the findings in this study?
Line 429: Differences in simulations results are described in detail. Can you add information at which order of magnitude differences in simulation results become relevant i.e. model results become insufficient for hazard management applications?
Fig. 7: Please add elevation profiles of DEMs.
Line 487: Please specify. What is the order of magnitude for gully features to be relevant in avalanche modeling?
Line 506: Please rephrase this sentence to be more clear.
Fig. 10: Please add an overview map with marked areas of shown subfigures for readers, who are not familiar with the test site.
# technical corrections
Line 35: cartesian coordinate system
Figure 3: Please use a different color for the fracture line for better visibility.
Fig. 9: Please add a blank between numbers and SI units.
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RC2: 'Comment on nhess-2022-97', Anonymous Referee #2, 02 May 2022
The manuscript aims at providing insights into the DEM generation process by various approaches and the effect of DEM resolution on the subsequent numerical modeling. The manuscript is well written and well organized, and the methods are well explained. The work is interesting; however, some minor parts have to be improved.
- Page 11, Line 285: “Holes were filled consistently by applying a max hole-filling threshold of 100 m2,…..”. It is a little bit unclear to me. What is the smallest and largest size encountered? What does it mean by “max hole filling threshold of 100 m2”, is this the largest hole size that can be filled? What technique is used? What are the advantages and drawbacks of the hole filling technique used? What impact did the hole-filling have on the modeling results? Also, any reference to available literature will be sufficient.
- Page 11, Line 272: In reference to comment #1, if there were holes encountered in the DEMs then how can be classified as “State of the art DEMs”?
- 2: demarcate the release zone and show the runout direction.
- Page 14, Line 354: Please provide the respective DOD and corresponding information.
- 4: it would be better to replace the figure with the time-lapse for the complete runout.
- Please provide the RAMMS input parameters in a tabulated form.
Aubrey Miller et al.
Aubrey Miller et al.
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