the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Autonomous and efficient large-scale snow avalanche monitoring with an Unmanned Aerial System (UAS)
Abstract. Large-scale monitoring is a crucial task for managing remote mountain environments, especially for hazardous events such as snow avalanches, debris flows or rockslides. One key information for safety-related applications is large-scale information on released avalanches. As avalanches occur in remote and potentially dangerous locations this data is difficult to obtain. Uncrewed fixed-wing aerial vehicles, due to their low cost, long range and high travel speeds are promising platforms to gather aerial imagery to map avalanche activity. However, autonomous flight in mountainous terrain remains a challenge due to the complex topography, regulations, and harsh weather conditions. In this work, we present a proof of concept system that is capable of safely navigating and mapping avalanches using a fixed-wing aerial system (UAS) and discuss the challenges arising for operating such a system. We show in our field experiments that we can effectively and safely navigate in steep mountain environments while maximizing the map quality and efficiency while meeting regulatory requirements. We expect our work to enable more autonomous operations of fixed-wing vehicles in alpine environments to maximize the quality of the data gathered. By enabling the acquisition of frequent and high quality information on avalanche activity, such drone systems would have a large impact of safety critical applications such as avalanche warning, mitigation measure planning or hazard mapping.
Competing interests: One of the co-authors is a member of the editorial board of Natural Hazards and Earth System Sciences.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.- Preprint
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RC1: 'Comment on egusphere-2024-2728', Thomas Van Der Weide, 04 Feb 2025
Thank you for your work and taking the time to share this research. The paper is structured well and has high quality figures which show the potential for a significant improvement in UAV mapping techniques.
3.1 route planning optimization section
It does make sense to try and maximize the number of ROIs visited per flight but since this can be calculated before take off I'd also like to see it optimized around the number of flights needed to cover all the ROIs. For instance since it’ll take two flights to cover all four ROIs could the route optimization cover E and I with a greater % coverage (mapping cost = 6) in one flight and D and G in another? This would also help ensure there's plenty of flight time since the optimization route from I to D passes right next to A. I'd also like to see some discussion about using a somewhat flexible but realistic flight time/range estimate to inform the route planning optimization instead of these being hard coded values.
3.2 Platform
Does it cruise at the same speed when collecting data as when traversing between study areas?
What is the DEM resolution and what terrain_spacing value was used?
You mention a 50km range but is this with 20% of the battery remaining when landing or how was this estimated?
4.3 Active Mapping
This is done in real-time using the onboard computer which is very cool and would definitely be a useful tool to ensure an area is fully covered before returning to home. In Figure 17 we see that the active mapping collected 67 images over the ROI instead of the 167 images mentioned before but both of these values are still significantly more than the 47 collected in the coverage mapping survey. Were these two surveys the same flight time and range so the resulting difference in the image count is solely because of how well the active mapping performed? Would a cross-grid coverage map have been a better comparison? Also, it should be mentioned somewhere what side lap % was used for the traditional coverage mapping survey.
Because you're working in Avalanche terrain I'm understanding that there's no mention of ground control points for a qualitative comparison between these two mapping methods and their resulting point clouds. One advantage of the coverage mapping method is that (ignoring wind) the UAV is mostly level when imaging which means the onboard GPS has a better sky view and position estimate. I'd be very interested to see some information about how imaging the hillside at an angle influenced your GPS accuracy which translates into your point cloud reconstruction uncertainty. Did you adjust for this difference in positional uncertainty between the methods in Agisoft? Since you used PPK were the images uploaded to Agisoft using their actual positional uncertainties? The Agisoft processing reports should also be included.
5. Discussion
Could this same mapping approach with high roll angles to image the hill side be calculated and used as a mapping tool in the mission planning software prior to taking off?
For more autonomous operations Active Mapping and the on-board computer could still be used to calculate the estimated coverage and direct the UAV to add flight lines to fill in the gaps after the survey if needed and if battery levels are sufficient?
6. Conclusion
"The field tests have also shown that the active mapping planner is capable of mapping an ROI with better reconstruction results, and potentially more efficiently." I do not agree that there's sufficient evidence provided to say that this method gives better reconstruction results. To do that you'd need ground control and validation points. This method has shown that with minimal user input active mapping can legally and safely fly a survey with good coverage.Citation: https://doi.org/10.5194/egusphere-2024-2728-RC1 -
RC2: 'Comment on egusphere-2024-2728', Madeline Lee, 09 Mar 2025
The authors have presented a good discussion on the importance of balancing efficiency and safety of UAV-flight operations in rough terrain with achieving the objective of reliable remotely-sensed imagery for avalanche monitoring and mapping. The presented methods may prove to be highly beneficial to reduce scientific data loss when a sensor trigger fails in flight or optimize flight paths to reduce uncertainty / increase image resolution based on real-time feedback of conditions. However, further field testing and quantitative image analysis is needed to fully demonstrate the advantage of the optimization algorithms. Below are minor considerations for the authors.
I. In-text Recommendations
L35: Replace 'manned' with 'crewed' considering UAS is uncrewed aircraft.
L88: Discussion on photogrammetry is presented, however there is no mention in the paper on the implementation of LiDAR and the resolution of photogrammetry to LiDAR, which would be relevant as a potential dataset for validation/comparison. For example: Solbakken, E. et al. (2024) Repeated UAS Lidar Scanning of Snow Surface to Support Site Specific Avalanche Warning.
L168: "We describe the system by describing the system".
L198: The mapping cost is highly variable, where it will differ per ROI. Further, there is no mention on flight direction, which is highly impacted by head or tail winds, especially within valleys.
L263: Acknowledgement of "unaccounted trees and obstructions not included in DEM", however pointing out relevant 'obstructions' is recommended. As this is a paper focused on avalanche terrain, there is no mention of the impact of snow height (except 'snow cover' in conclusion) and avalanche debris. The DEM will represent a 'snow free' interpretation of the surface, however the UAV will be operated above snow covered terrain. This additional height above surface should be acknowledged earlier in the paper and impact on flight altitude above ground level. Additionally, in zones of high avalanche activity, the surface is dynamic and large rock debris may exist causing the DEM to be out of date.
L345: "The extent was outlined by hand". On what dataset (aerial, satellite) was the extent determined?
L438: Consider a comparison with at least a grid difference where areas of disagreement or lower uncertainty can be more clearly identified. Perhaps the areas of disagreement are correlated to slope or flight angle, etc.
L444: "fraction of the time" - What is the time difference needed to accomplish the 67 active mapping images versus the 47 coverage mapping images?
L513: Consider additional quantitative means to validate the quality of the reconstruction. In addition to simple grid differencing, other remotely sensed/geophysical data sets may be acquired by drone. LiDAR, as suggested above, may have a very high resolution result that can act as a baseline to which active and coverage mapping results is compared. Another is ground penetrating radar, GPR. Although GPR is suited for rotary-wing and not ideal for extended coverage by a FW, it can be used for a small scale validation of photogrammetry results. It can also validate the DEMs since GPR will provide a snapshot of the current ground conditions below the snow cover.
II. Suggestions for Figures
Figure 1. Captions under each image pane in addition to the full caption is redundant, and can be minimized to a, b, c
Figure 2. Although mentioned in text, the addition of a scalebar to b) to provide context on wingspan / aircraft size.
Figure 3. ROIs are labeled
Figure 16. Label which sides of the figure are active and coverage mapping with a, b or left, right. Recommend same colour scale for all grids, as viridis is perceptually uniform sequential but rainbow/spectral is not, so anomalies are presented differently.
Citation: https://doi.org/10.5194/egusphere-2024-2728-RC2
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