the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 02 May 2022
Brief Communication: An Autonomous UAV for Catchment-Wide Monitoring of a Debris Flow Torrent
Elias Hodel
Erik Mannerfelt
Nicolas Ackermann
Kristen Cook
Michael Dietze
Livia Estermann
Daniel Farinotti
Martin Fengler
Lukas Hammerschmidt
Flavia Hänsli
Jacob Hirschberg
Brian McArdell
Peter Molnar
Abstract. Debris flows threaten communities in mountain regions worldwide. Combining modern photogrammetric processing with autonomous unmanned aerial vehicle (UAV) flights at sub-weekly intervals allows mapping of sediment dynamics in a debris flow catchment. This provides important information for sediment disposition that pre-conditions the catchment for debris flow occurrence. At the Illgraben debris-flow catchment in Switzerland, our autonomous UAV launched nearly 50 times in the snow-free periods in 2019–2021 with typical flight intervals of 2–4 days, producing 350–400 images every flight. The observed terrain-changes resulting from debris flows exhibit preferred locations of erosion and deposition, including memory effects as previously deposited material is preferentially removed during subsequent debris flows. Such data are critical for the validation of geomorphological process models. Given the remote terrain, the mapped short-term erosion and deposition structures are difficult to obtain with conventional measurements. The proposed method thus fills an observational gap, which ground-based monitoring and satellite based remote sensing cannot fill as a result of limited access, reaction time, spatial resolution, or involved costs.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(31703 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(31703 KB) - BibTeX
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- Final revised paper
Journal article(s) based on this preprint
Fabian Walter et al.
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2022-156', Marcel Hürlimann, 12 May 2022
General comments
This “Brief communication” presents a novel technique that enables the monitoring of sediment dynamics in remote terrains. It combines photogrammetric processing with UAV and was tested in the Illgraben debris-flow torrent, located in Switzerland. The topic is perfectly fitting with the ones proposed by NHESS and the contents are relevant for researchers and practitioners. I recommend the publication of the ms after some minor revisions.
- I suggest adding some information on recent studies applying UAV (or TLS) in torrential or fluvial areas (not related to Illgraben).
- The (preliminary) results, described between L125 and 131, should be extended and placed in a separate section. The results are brilliant and deserve a longer description. Not only related to the sediment dynamics, but also on basic (more technical) information like the pixel size of the DEM, which is missing.
If the above two points are not possible due to space problems, try to reduce other parts of introduction or discussion-conclusions.
- The description of locations like Illgraben mouth, channel outlet, upper catchment, head of the Illgraben channel, catchment outlet are not always clear. The authors may simplify them and add the most important ones in Figure 1A.
Specific comments:
L30: “DURING debris flows” is not clear. The surveys were before and after debris-flow events, weren’t they?
L73: width not with
L84-85: not totally clear, which was finally used in Illgraben (LAN or/and GSM).
L89: “1-inch Complementary Metal Oxide Semiconductor sensor” only expert may understand it. Please clarify.
L125: Figure 2 (not 1).
Figure 2: Improve the design or layout (e.g. rotate the zoom boxes and make them larger). Clearly indicate the locations of the check dams.
L140: You only mention flight time, but it would also be interesting having some information on the time consumption of the photogrammetric processing.
Citation: https://doi.org/10.5194/egusphere-2022-156-RC1 -
AC1: 'Reply on RC1', Fabian Walter, 15 Aug 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-156/egusphere-2022-156-AC1-supplement.pdf
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CC1: 'Comment on egusphere-2022-156', Alexander Raphael Groos, 02 Jul 2022
In this ‘brief communication’, Walter et al. introduce a new technique for (semi-)autonomous high-resolution monitoring of sediment dynamics in remote alpine terrain based on UAV remote sensing and photogrammetry. The presented system consists of a hexacopter and a base station that facilitates automatic recharging and acts as an operational relay between the UAV and a remote operator, who is in charge of the flight monitoring. From a technical and operational point of view, a remote operator would not be necessary within this framework, but supervision by a human is still mandatory for (autonomous) UAV missions beyond visual line of sight. The feasibility of the approach has been successfully demonstrated at the Illgraben debris-flow catchment in Switzerland and paves the way for (semi-)autonomous UAV-based monitoring in other contexts and terrains.
In addition to the comments of Reviewer 1, I have some (rather technical) remarks and questions that might be of interest for some readers:
1) A limited durability and replacement of some system components is mentioned in the text (L93-94). Which components were less reliable or failing and how often had the base station to be serviced during the summer months? The maintenance aspect would be especially important for autonomous operations in even more remote locations where the frequent replacement of components is difficult.
2) Had the remote operator/observer in the control centre in St. Gallen ever to intervene during the three-year period? Has the remote operator/observer full control over the UAV and what would happen in the case of an (unlikely) emergency (e.g. bird attack or curious people/animals approaching the base station during the survey or landing process)? I assume the base station is fenced. Is this correct?
3) Can you say anything about the precise and autonomous landing of the copter: is the RTK GNSS in combination with a vision-based tracking system used for this purpose?
4) Does the base station rely on an external power supply or is it connected to solar panels and a power station (not shown in Fig. 1)?
5) I’m aware that the selected manuscript type has a strict page limit, but I am missing a brief discussion on similar approaches/applications (i.e. semi-autonomous UAV monitoring) in the geosciences.
Wording: Unoccupied Aerial Vehicle is increasingly used in the (geo)scientific community as a more neutral term for UAV (Joyce et al., 2021: https://doi.org/10.3390/drones5010021) and I therefore suggest to adopt it.
Citation: https://doi.org/10.5194/egusphere-2022-156-CC1 -
AC2: 'Reply on CC1', Fabian Walter, 15 Aug 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-156/egusphere-2022-156-AC2-supplement.pdf
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AC2: 'Reply on CC1', Fabian Walter, 15 Aug 2022
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RC2: 'Comment on egusphere-2022-156', Velio Coviello, 07 Jul 2022
In their short communication, Walter et al. present a UAV-based semi-automatic system for the multi-temporal topographic monitoring of sediment dynamics in the source areas of a debris-flow basin. The study presents preliminary results on the erosion/deposition processes in the analyzed time period and explores the potential of the technique for investigating debris-flow hazards. The format of the short communication is suitable for this manuscript, the text is well written, and the presented system is definitely unique.
In addition to the comments of the other reviewers, on which I agree, I have few minor remarks that might be considered prior to publication. Section 5 Discussion and Conclusion sounds very optimistic for what concerns the future application of the technique in other contexts. I would suggest to briefly discuss also the potential limitations of the proposed system. For instance, I wonder to what extend the proposed technique is replicable in other locations given the installation, maintenance and data-processing costs. Regarding the assessment of debris-flow hazards in the aftermath of an event, the continuous monitoring of the unstable slope with ground-based systems (with radar, seismic but also photogrammetric sensors) is not, in general, more suitable?
Citation: https://doi.org/10.5194/egusphere-2022-156-RC2 -
AC3: 'Reply on RC2', Fabian Walter, 15 Aug 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-156/egusphere-2022-156-AC3-supplement.pdf
-
AC3: 'Reply on RC2', Fabian Walter, 15 Aug 2022
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2022-156', Marcel Hürlimann, 12 May 2022
General comments
This “Brief communication” presents a novel technique that enables the monitoring of sediment dynamics in remote terrains. It combines photogrammetric processing with UAV and was tested in the Illgraben debris-flow torrent, located in Switzerland. The topic is perfectly fitting with the ones proposed by NHESS and the contents are relevant for researchers and practitioners. I recommend the publication of the ms after some minor revisions.
- I suggest adding some information on recent studies applying UAV (or TLS) in torrential or fluvial areas (not related to Illgraben).
- The (preliminary) results, described between L125 and 131, should be extended and placed in a separate section. The results are brilliant and deserve a longer description. Not only related to the sediment dynamics, but also on basic (more technical) information like the pixel size of the DEM, which is missing.
If the above two points are not possible due to space problems, try to reduce other parts of introduction or discussion-conclusions.
- The description of locations like Illgraben mouth, channel outlet, upper catchment, head of the Illgraben channel, catchment outlet are not always clear. The authors may simplify them and add the most important ones in Figure 1A.
Specific comments:
L30: “DURING debris flows” is not clear. The surveys were before and after debris-flow events, weren’t they?
L73: width not with
L84-85: not totally clear, which was finally used in Illgraben (LAN or/and GSM).
L89: “1-inch Complementary Metal Oxide Semiconductor sensor” only expert may understand it. Please clarify.
L125: Figure 2 (not 1).
Figure 2: Improve the design or layout (e.g. rotate the zoom boxes and make them larger). Clearly indicate the locations of the check dams.
L140: You only mention flight time, but it would also be interesting having some information on the time consumption of the photogrammetric processing.
Citation: https://doi.org/10.5194/egusphere-2022-156-RC1 -
AC1: 'Reply on RC1', Fabian Walter, 15 Aug 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-156/egusphere-2022-156-AC1-supplement.pdf
-
CC1: 'Comment on egusphere-2022-156', Alexander Raphael Groos, 02 Jul 2022
In this ‘brief communication’, Walter et al. introduce a new technique for (semi-)autonomous high-resolution monitoring of sediment dynamics in remote alpine terrain based on UAV remote sensing and photogrammetry. The presented system consists of a hexacopter and a base station that facilitates automatic recharging and acts as an operational relay between the UAV and a remote operator, who is in charge of the flight monitoring. From a technical and operational point of view, a remote operator would not be necessary within this framework, but supervision by a human is still mandatory for (autonomous) UAV missions beyond visual line of sight. The feasibility of the approach has been successfully demonstrated at the Illgraben debris-flow catchment in Switzerland and paves the way for (semi-)autonomous UAV-based monitoring in other contexts and terrains.
In addition to the comments of Reviewer 1, I have some (rather technical) remarks and questions that might be of interest for some readers:
1) A limited durability and replacement of some system components is mentioned in the text (L93-94). Which components were less reliable or failing and how often had the base station to be serviced during the summer months? The maintenance aspect would be especially important for autonomous operations in even more remote locations where the frequent replacement of components is difficult.
2) Had the remote operator/observer in the control centre in St. Gallen ever to intervene during the three-year period? Has the remote operator/observer full control over the UAV and what would happen in the case of an (unlikely) emergency (e.g. bird attack or curious people/animals approaching the base station during the survey or landing process)? I assume the base station is fenced. Is this correct?
3) Can you say anything about the precise and autonomous landing of the copter: is the RTK GNSS in combination with a vision-based tracking system used for this purpose?
4) Does the base station rely on an external power supply or is it connected to solar panels and a power station (not shown in Fig. 1)?
5) I’m aware that the selected manuscript type has a strict page limit, but I am missing a brief discussion on similar approaches/applications (i.e. semi-autonomous UAV monitoring) in the geosciences.
Wording: Unoccupied Aerial Vehicle is increasingly used in the (geo)scientific community as a more neutral term for UAV (Joyce et al., 2021: https://doi.org/10.3390/drones5010021) and I therefore suggest to adopt it.
Citation: https://doi.org/10.5194/egusphere-2022-156-CC1 -
AC2: 'Reply on CC1', Fabian Walter, 15 Aug 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-156/egusphere-2022-156-AC2-supplement.pdf
-
AC2: 'Reply on CC1', Fabian Walter, 15 Aug 2022
-
RC2: 'Comment on egusphere-2022-156', Velio Coviello, 07 Jul 2022
In their short communication, Walter et al. present a UAV-based semi-automatic system for the multi-temporal topographic monitoring of sediment dynamics in the source areas of a debris-flow basin. The study presents preliminary results on the erosion/deposition processes in the analyzed time period and explores the potential of the technique for investigating debris-flow hazards. The format of the short communication is suitable for this manuscript, the text is well written, and the presented system is definitely unique.
In addition to the comments of the other reviewers, on which I agree, I have few minor remarks that might be considered prior to publication. Section 5 Discussion and Conclusion sounds very optimistic for what concerns the future application of the technique in other contexts. I would suggest to briefly discuss also the potential limitations of the proposed system. For instance, I wonder to what extend the proposed technique is replicable in other locations given the installation, maintenance and data-processing costs. Regarding the assessment of debris-flow hazards in the aftermath of an event, the continuous monitoring of the unstable slope with ground-based systems (with radar, seismic but also photogrammetric sensors) is not, in general, more suitable?
Citation: https://doi.org/10.5194/egusphere-2022-156-RC2 -
AC3: 'Reply on RC2', Fabian Walter, 15 Aug 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-156/egusphere-2022-156-AC3-supplement.pdf
-
AC3: 'Reply on RC2', Fabian Walter, 15 Aug 2022
Peer review completion
Journal article(s) based on this preprint
Fabian Walter et al.
Fabian Walter et al.
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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