Fixed photogrammetric systems for natural hazard monitoring with high spatio-temporal resolution

Blanch, Xabier; Guinau, Marta; Eltner, Anette; Abellan, Antonio

doi:https://doi.org/10.5194/nhess-2023-79

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https://doi.org/10.5194/nhess-2023-79

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27 Jun 2023

| 27 Jun 2023

Status: a revised version of this preprint was accepted for the journal NHESS and is expected to appear here in due course.

Fixed photogrammetric systems for natural hazard monitoring with high spatio-temporal resolution

Xabier Blanch, Marta Guinau, Anette Eltner, and Antonio Abellan

Abstract. In this publication we address the lack of knowledge in the design and construction of photogrammetric systems for high spatio-temporal resolution rockfall monitoring. Accordingly, we provide in-depth information on the components, assembly instructions, and programming codes required to build them, making them accessible to researchers from different disciplines who are interested in 3D change-detection monitoring. Each system comprises five photographic modules and a wireless transmission system for real-time image transfer. As an alternative to LiDAR (Light Detection and Ranging), high-end digital cameras offer a simpler and more cost-effective solution for the generation of 3D models, especially in fixed time-lapse monitoring systems. The acquired images, in combination with algorithms that allow the creation of improved 3D models, offer change detection performance comparable to LiDAR. We showcase the usefulness of our approach by presenting real-world applications in the field of geohazards monitoring. Our findings highlight the potential of our method to detect pre-failure deformation and identify rockfalls with a theoretical change-detection threshold of only 3–4 cm, thereby demonstrating the potential to achieve similar accuracies to LiDAR but at a much lower cost. Furthermore, thanks to the higher data acquisition frequency, the results show how the overlap of events that leads to an erroneous interpretation of the behaviour of the active area is minimized, allowing, for example, more accurate correlations between weather conditions and rockfall activity.

Received: 17 May 2023 – Discussion started: 27 Jun 2023

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Xabier Blanch et al.

Status: closed

RC1:
'Comment on nhess-2023-79', Anonymous Referee #1, 16 Jul 2023
General comments:
The paper by Blanch et al. entitled “Fixed photogrammetric systems for natural hazard monitoring with high spatio-temporal resolution” presents the design and construction of photogrammetric systems for high spatial-temporal resolution rockfall monitoring in two study areas in Spain. The monitoring systems have been installed in front of rockfall active cliffs and have been in operation for over a year. The authors provided in-depth information on the components, assembly instructions, and programming codes required to build the photogrammetric monitoring system with an implementation in real scenarios.
Overall, this is an appropriate subject area for NHESS journal, and the developed workflow, accessible to researchers from different disciplines, could help data collection and the 3D change-detection surveys, fundamental in terms of risk monitoring and prevention perspective. The manuscript is well-written and developed even for inexperienced readers. However, I believe that minor improvements can be made, for example, adding some aspects related to data post-processing and error assessment of photogrammetry outputs. Moreover, it is also required to add some details of previous works (only referenced in the manuscript) to have a complete understanding of the whole research. This work can be interesting and useful for the scientific community with some improvements.
Specific comments:
Results:
Line 285-295: It could be useful for the reader to have maps of the study areas with the location of the camera’s network used for monitoring because the mere reference to previous work (Blanch et al., 2020) is not sufficient for the manuscript to have its own independence in understanding the carried-out study.

Line 299: Please briefly explain the workflow and acronym. The citation alone is not sufficient to ensure an understanding of the work done independently of previous work. In this way, the reader can better understand the study.

Line 303: Where are the GCPs located in the study area (a figure could be added about this)? Is it a network of fixed points? Did you use also independent Check Points (CPs) in the photogrammetric workflow? They are fundamental to understanding the errors and accuracy of the point cloud.

Has the problem of co-registration of point clouds been considered in the multi-temporal 3D surveys? This problem could affect the measure of the minimum change detection value between multi-temporal point clouds.

Conclusions: could be expanded with more details to emphasize the innovative and useful points of the work done.

Typing errors
Line 298: 2 cm/pixel or 2 cm pixel^-1

Line 301: error of 0.23 m?? (units of measurement are missing)

Line 302: what does "Mio points" stand for?

Line 302: 6000 points/m² or 6000 points m^-2
Citation: https://doi.org/10.5194/nhess-2023-79-RC1
- AC1: 'Reply on RC1', Xabier Blanch Gorriz, 05 Aug 2023
  
  Thank you for taking the time to provide your constructive feedback on our manuscript and for making it promptly. We really appreciate your acknowledgment of the paper's relevance to NHESS and its accessibility for researchers from diverse backgrounds. Your comments will certainly improve the quality of our manuscript. We will not provide you a long answer because we agree with most of your advice, and we will apply it.
  Regarding your general comments, in the upcoming version of the manuscript, we will expand the photogrammetric processing explanation. While a significant part relies on previous publications (Blanch et al., 2020), we will incorporate more descriptive explanations to ensure a smoother understanding of the processing steps.
  Lines 285-295: One of the article's objectives was to segregate the methodology from the specific studies areas. However, your comment has highlighted its importance for a better understanding. Therefore, we will include maps of the two study areas illustrating camera network locations in the supplemental material .
  Line 299: In line with your general comment and that of reviewer 2, we will provide a brief explanation of the workflow and acronyms to ensure a better understanding of photogrammetric postprocessing.
  Line 303: The two analyzed study areas do not allow for GCP installation on the rock walls. Thus, we've employed a virtual GCP strategy (Stöcker et al., 2015). We will add further details about this virtual GCP approach in the upcoming version of the manuscript.
  Regarding your question with the co-registration problem: Yes, thanks to the use of the MEMI algorithm (from previous work), the co-registration issue is eliminated. The determination of the internal and external camera parameters is done simultaneously for the different multi-temporal captures, ensuring that the 3D models are reconstructed with the same camera locations, which guarantees a perfect co-registration and does not require any further processing/algorithm (e.g., ICP).
  Typos: We will fix all typographical errors identified.
  We sincerely appreciate your comments and your efforts to improve the quality of our article. Please do not hesitate to contact us for any clarification or comments.
  
  Citation: https://doi.org/10.5194/nhess-2023-79-AC1
RC2:
'Comment on nhess-2023-79', Anonymous Referee #2, 27 Jul 2023
In their manuscript, Blanch et al. present a detailed description of how to construct and operate cost-efficient photogrammetric systems, essentially a set of synchronized high-resolution time-lapse cameras. Using data from two study sites in Spain, they show that their synchronized setups of cameras attain similar accuracies in 3D change detection monitoring as terrestrial LiDAR, with the advantage of cost efficiency and higher temporal resolution. Their primary aim is to enable other researchers to set up similar systems. For this, the authors provide details on the components used and tested for their setups, give assembly instructions, and share the programming code needed for the operation.
The manuscript is well very written and clearly merits publication in NHESS as it facilitates the installation of low-cost monitoring systems by a larger community. Their setup can be built with a few hundred Euros and is applicable to monitoring of a wide range of environmental processes. Before acceptable for publication, the authors need to address a number of issues that I will outline below. As these are only minor points (see below and attached PDF), I recommend “minor revisions”.
Kind regards

General comments
Chapter 2: In this chapter the authors provide a great amount of detail on the components used in their setup, on the assemblage and functionality of the system and the proposed workflow, which allows the reader (also the non-expert) to follow in detail. What I am missing here are details on the processing of the images in the next steps. Surely, the aim of the authors is to provide instructions for setting up a photogrammetric system, not going into details on the generation of digital topography from the images acquired. However, as the Chapter 3 looks at the accuracies of the models that can be attained, it would be nice to at least provide some short paragraph on the workflow and settings used for the generation of 3D models. The same applies for the M3C2 algorithm; here the authors point to the fact that the settings have a crucial influence on the results – providing those details for the examples would be very much appreciated.

L212-214 and L239-244: This only becomes clear later in the text. Maybe the authors could also indicate at this point that the idea of this second relay is to trigger it by running a code in the case that the system should not shut down automatically.

L439-455: As the paper is rather focusing on the technical aspects of the setup, this section comes a bit as a surprise. While I think some of the points are valid, they would require an in-depth analysis. I would recommend leaving out this section here and focus on the discussion.
Citation: https://doi.org/10.5194/nhess-2023-79-RC2
- AC2: 'Reply on RC2', Xabier Blanch Gorriz, 05 Aug 2023
  
  Thank you for dedicating your time and effort to reviewing the manuscript and for providing constructive feedback. The authors believe that your contributions will enhance our publication. We also appreciate your clarity in assessing the fit for the NHESS journal. We are grateful for the minor revisions made in the PDF document attached to your comments. All the mentioned points will be modified, corrected, or expanded in the upcoming version of the manuscript.
  Regarding the specific comments from your review, we provide a brief reply because we agree with all your comments, and we will apply them.
  Chapter 2: We appreciate your comment, which aligns with the Reviewer 1. Both reviewers have highlighted the need to expand the workflow explanation and the post-processing steps used to obtain the results. The upcoming version of the manuscript, we will expand the photogrammetric processing explanation. While a significant part relies on previous publications (Blanch et al., 2020), we will incorporate more descriptive explanations to ensure a smoother understanding of the processing steps.
  Lines 212-214 and 239-244: Your observation is accurate. We will include this reasoning, ensuring that readers understand from the beginning the use of this second relay.
  Lines 439-455: We appreciate your input on these lines, and we understand the surprise at finding these two paragraphs in the discussion. We will critically review the content to determine what can be omitted. We agree that it is not appropriate to discuss any topic that has not been introduced in the methodology or results sections.
  We sincerely appreciate your comments and your efforts to improve the quality of this manuscript. Please do not hesitate to contact us for any clarification or comments
  
  Citation: https://doi.org/10.5194/nhess-2023-79-AC2

Status: closed

RC1:
'Comment on nhess-2023-79', Anonymous Referee #1, 16 Jul 2023
General comments:
The paper by Blanch et al. entitled “Fixed photogrammetric systems for natural hazard monitoring with high spatio-temporal resolution” presents the design and construction of photogrammetric systems for high spatial-temporal resolution rockfall monitoring in two study areas in Spain. The monitoring systems have been installed in front of rockfall active cliffs and have been in operation for over a year. The authors provided in-depth information on the components, assembly instructions, and programming codes required to build the photogrammetric monitoring system with an implementation in real scenarios.
Overall, this is an appropriate subject area for NHESS journal, and the developed workflow, accessible to researchers from different disciplines, could help data collection and the 3D change-detection surveys, fundamental in terms of risk monitoring and prevention perspective. The manuscript is well-written and developed even for inexperienced readers. However, I believe that minor improvements can be made, for example, adding some aspects related to data post-processing and error assessment of photogrammetry outputs. Moreover, it is also required to add some details of previous works (only referenced in the manuscript) to have a complete understanding of the whole research. This work can be interesting and useful for the scientific community with some improvements.
Specific comments:
Results:
Line 285-295: It could be useful for the reader to have maps of the study areas with the location of the camera’s network used for monitoring because the mere reference to previous work (Blanch et al., 2020) is not sufficient for the manuscript to have its own independence in understanding the carried-out study.

Line 299: Please briefly explain the workflow and acronym. The citation alone is not sufficient to ensure an understanding of the work done independently of previous work. In this way, the reader can better understand the study.

Line 303: Where are the GCPs located in the study area (a figure could be added about this)? Is it a network of fixed points? Did you use also independent Check Points (CPs) in the photogrammetric workflow? They are fundamental to understanding the errors and accuracy of the point cloud.

Has the problem of co-registration of point clouds been considered in the multi-temporal 3D surveys? This problem could affect the measure of the minimum change detection value between multi-temporal point clouds.

Conclusions: could be expanded with more details to emphasize the innovative and useful points of the work done.

Typing errors
Line 298: 2 cm/pixel or 2 cm pixel^-1

Line 301: error of 0.23 m?? (units of measurement are missing)

Line 302: what does "Mio points" stand for?

Line 302: 6000 points/m² or 6000 points m^-2
Citation: https://doi.org/10.5194/nhess-2023-79-RC1
- AC1: 'Reply on RC1', Xabier Blanch Gorriz, 05 Aug 2023
  
  Thank you for taking the time to provide your constructive feedback on our manuscript and for making it promptly. We really appreciate your acknowledgment of the paper's relevance to NHESS and its accessibility for researchers from diverse backgrounds. Your comments will certainly improve the quality of our manuscript. We will not provide you a long answer because we agree with most of your advice, and we will apply it.
  Regarding your general comments, in the upcoming version of the manuscript, we will expand the photogrammetric processing explanation. While a significant part relies on previous publications (Blanch et al., 2020), we will incorporate more descriptive explanations to ensure a smoother understanding of the processing steps.
  Lines 285-295: One of the article's objectives was to segregate the methodology from the specific studies areas. However, your comment has highlighted its importance for a better understanding. Therefore, we will include maps of the two study areas illustrating camera network locations in the supplemental material .
  Line 299: In line with your general comment and that of reviewer 2, we will provide a brief explanation of the workflow and acronyms to ensure a better understanding of photogrammetric postprocessing.
  Line 303: The two analyzed study areas do not allow for GCP installation on the rock walls. Thus, we've employed a virtual GCP strategy (Stöcker et al., 2015). We will add further details about this virtual GCP approach in the upcoming version of the manuscript.
  Regarding your question with the co-registration problem: Yes, thanks to the use of the MEMI algorithm (from previous work), the co-registration issue is eliminated. The determination of the internal and external camera parameters is done simultaneously for the different multi-temporal captures, ensuring that the 3D models are reconstructed with the same camera locations, which guarantees a perfect co-registration and does not require any further processing/algorithm (e.g., ICP).
  Typos: We will fix all typographical errors identified.
  We sincerely appreciate your comments and your efforts to improve the quality of our article. Please do not hesitate to contact us for any clarification or comments.
  
  Citation: https://doi.org/10.5194/nhess-2023-79-AC1
RC2:
'Comment on nhess-2023-79', Anonymous Referee #2, 27 Jul 2023
In their manuscript, Blanch et al. present a detailed description of how to construct and operate cost-efficient photogrammetric systems, essentially a set of synchronized high-resolution time-lapse cameras. Using data from two study sites in Spain, they show that their synchronized setups of cameras attain similar accuracies in 3D change detection monitoring as terrestrial LiDAR, with the advantage of cost efficiency and higher temporal resolution. Their primary aim is to enable other researchers to set up similar systems. For this, the authors provide details on the components used and tested for their setups, give assembly instructions, and share the programming code needed for the operation.
The manuscript is well very written and clearly merits publication in NHESS as it facilitates the installation of low-cost monitoring systems by a larger community. Their setup can be built with a few hundred Euros and is applicable to monitoring of a wide range of environmental processes. Before acceptable for publication, the authors need to address a number of issues that I will outline below. As these are only minor points (see below and attached PDF), I recommend “minor revisions”.
Kind regards

General comments
Chapter 2: In this chapter the authors provide a great amount of detail on the components used in their setup, on the assemblage and functionality of the system and the proposed workflow, which allows the reader (also the non-expert) to follow in detail. What I am missing here are details on the processing of the images in the next steps. Surely, the aim of the authors is to provide instructions for setting up a photogrammetric system, not going into details on the generation of digital topography from the images acquired. However, as the Chapter 3 looks at the accuracies of the models that can be attained, it would be nice to at least provide some short paragraph on the workflow and settings used for the generation of 3D models. The same applies for the M3C2 algorithm; here the authors point to the fact that the settings have a crucial influence on the results – providing those details for the examples would be very much appreciated.

L212-214 and L239-244: This only becomes clear later in the text. Maybe the authors could also indicate at this point that the idea of this second relay is to trigger it by running a code in the case that the system should not shut down automatically.

L439-455: As the paper is rather focusing on the technical aspects of the setup, this section comes a bit as a surprise. While I think some of the points are valid, they would require an in-depth analysis. I would recommend leaving out this section here and focus on the discussion.
Citation: https://doi.org/10.5194/nhess-2023-79-RC2
- AC2: 'Reply on RC2', Xabier Blanch Gorriz, 05 Aug 2023
  
  Thank you for dedicating your time and effort to reviewing the manuscript and for providing constructive feedback. The authors believe that your contributions will enhance our publication. We also appreciate your clarity in assessing the fit for the NHESS journal. We are grateful for the minor revisions made in the PDF document attached to your comments. All the mentioned points will be modified, corrected, or expanded in the upcoming version of the manuscript.
  Regarding the specific comments from your review, we provide a brief reply because we agree with all your comments, and we will apply them.
  Chapter 2: We appreciate your comment, which aligns with the Reviewer 1. Both reviewers have highlighted the need to expand the workflow explanation and the post-processing steps used to obtain the results. The upcoming version of the manuscript, we will expand the photogrammetric processing explanation. While a significant part relies on previous publications (Blanch et al., 2020), we will incorporate more descriptive explanations to ensure a smoother understanding of the processing steps.
  Lines 212-214 and 239-244: Your observation is accurate. We will include this reasoning, ensuring that readers understand from the beginning the use of this second relay.
  Lines 439-455: We appreciate your input on these lines, and we understand the surprise at finding these two paragraphs in the discussion. We will critically review the content to determine what can be omitted. We agree that it is not appropriate to discuss any topic that has not been introduced in the methodology or results sections.
  We sincerely appreciate your comments and your efforts to improve the quality of this manuscript. Please do not hesitate to contact us for any clarification or comments
  
  Citation: https://doi.org/10.5194/nhess-2023-79-AC2

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Short summary

We present a cost-effective photogrammetric systems for high-resolution rockfall monitoring. The paper outlines the components, assembly, and programming codes required to build these systems. The systems utilize prime cameras to generate 3D models, offering comparable performance to LiDAR for change detection monitoring. Real-world applications highlight their potential in geohazards monitoring, enabling accurate detection of pre-failure deformation and rockfalls with a high temporal resolution.


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